Release v2.28.0

- rsync-parity cycle: differential parity gate + tracks 1-6
- protocol 2.28.0 (batched wire changes)
- --delete defaults to delete-during; new --delete-commit, --verify-basis
- parity matrix 116/14/27 of 157
- tested: unit, integration, ASan, strict differential parity

CHANGELOG.md

@@ -4,8 +4,91 @@ All notable changes to FastSync are documented here. Versions match
 `PROTOCOL_VERSION` (printed by `fastsync --version`); the client and server must
 run the same version because the handshake is strict.
 
+## [2.28.0] - 2026-09-20
+
+The rsync-parity cycle. `PROTOCOL_VERSION` moves `2.26.0 → 2.27.0 → 2.28.0`;
+client and server must run the same version (the handshake is strict). See
+`RSYNC_COMPAT.md` for the per-option matrix, now **116 ✅ / 14 ⚠️ / 27 ❌** of
+157 rows.
+
+### Added
+
+- **Differential rsync 3.4.1 parity gate** (`tests/integration/
+  test_differential_parity.py`, `parity_harness.py`, `parity_caveats.py`): runs
+  real `rsync` and FastSync over generated corpora and diffs the destination
+  tree, normalized stdout and exit code. A fast subset runs on pull requests and
+  the full strict set on push; the residual allowlist is empty.
+- FastSync-only long option **`--verify-basis`**: require a
+  `--compare-dest`/`--copy-dest`/`--link-dest` hit to match the source by
+  whole-file digest instead of trusting the size+mtime quick-check.
+- FastSync-only long option **`--delete-commit`** (implies `--delete`): the old
+  atomic late whole-tree commit.
+- `--bwlimit` now parses rsync's units exactly and paces like rsync's leaky
+  bucket; `--ignore-errors` reproduces rsync's skip-unreadable-subdir and
+  IO-error-suppressed deletion (exit 23).
+- `--info=name/flist/del/remove/nonreg/progress` emit rsync's line format,
+  including real-run `deleting`/`*deleting` lines carried by a new
+  `report_deletes` wire bool.
+- Receiver-observed `--stats` counters: `Number of created files` now carries
+  rsync's `(reg/dir/link/special)` breakdown and `Literal data` is exact for a
+  delta transfer (extended `STATUS_STATS`).
+- `--progress` uses an opt-in paths-only pre-count so the `to-chk` denominator
+  counts every entry like rsync, and emits per-directory/symlink/special names.
+- Receiver-side `protect`/`risk` filter engine (new bounded filter-rule wire
+  block): `--filter='P ...'` now shields a destination-only entry like rsync.
+- `auto` for `--compress-choice`/`--checksum-choice` honors
+  `RSYNC_COMPRESS_LIST`/`RSYNC_CHECKSUM_LIST`, and per-codec compression-level
+  defaults match rsync.
+- Empty source directories are recreated recursively; `-R --no-implied-dirs
+  --files-from` places listed files under missing implied parents; `--iconv`
+  matches rsync's push direction; `--delete-delay` reports actual removals and
+  recursively removes a refilled deferred directory.
+
+### Changed
+
+- **`--delete` now defaults to delete-during (rsync `--del`) timing.** With no
+  explicit timing flag, a plain `--delete` removes each directory's extras as
+  that directory is processed instead of committing one whole-tree deletion only
+  after the entire transfer succeeds. This matches rsync, frees destination
+  space progressively, and avoids the whole-old+new-tree peak that could
+  `ENOSPC` a tight destination. The client maps the default onto the existing
+  `delete_during` wire boolean, so `PROTOCOL_VERSION` stays `2.28.0`.
+- Basis directories (`--compare-dest`/`--copy-dest`/`--link-dest`) now default
+  to rsync's metadata quick-check (equal size and mtime; `--size-only` drops the
+  mtime leg) instead of FastSync's historical always-verify content hash.
+  `--copy-dest` re-applies the source attributes, and basis materialization is
+  streamed so the 256 MiB whole-file cap no longer applies to a basis hit.
+- The per-directory `STATUS_DELETE_PLAN` frame gained a one-int `apply` flag:
+  the one-shot per-run config block (protected prefixes, size-pruned mirrors,
+  `--delete-missing-args` exact paths) is now always transmitted first on a
+  config-only carrier (`apply=false`), fixing a latent bug where a
+  `--delete-missing-args` run whose `--files-from` list synchronized no directory
+  never sent its exact deletions.
+
+### Notes
+
+- `--delete`/`--delete-during` remain caveats for the mid-transfer abort
+  boundary (rsync's generator removes all planned extras ahead of its throttled
+  sender; FastSync removes only reached directories — final trees agree).
+  `--delete-before`, `--progress`, `--stats`, `--fuzzy` and the basis rows keep
+  their documented residuals in `RSYNC_COMPAT.md`; `--filter` and
+  `--delete-excluded` are now parity, including protection of a destination-only
+  excluded entry under default `--delete`.
+
+### Migration
+
+- Scripts that relied on plain `--delete` deleting nothing until the transfer
+  fully succeeded must pass **`--delete-commit`** (or `--delete-after`) to keep
+  that behavior. Plain `--delete` now removes reached directories' extras during
+  the transfer, exactly like rsync's default; on a completed run the final tree
+  is unchanged.
+- Deployments that relied on FastSync's stricter basis verification should pass
+  **`--verify-basis`**; the default now trusts the size+mtime quick-check like
+  rsync.
+
 ## [2.26.0] - 2026-09-17
 
+
 ### Added
 
 - **Parity-completion wave.** Closed the remaining rsync-parity gaps against

HANDOFF.md

@@ -1,16 +1,19 @@
-# FastSync — Session Handoff (2026-09-17)
+# FastSync — Session Handoff (2026-09-19)
 
 ## Current status
-- **Release `v2.21.0`** tagged (`919a729`, "Release v2.21.0"); full CI green
-  (run 552: lint, build-and-test, ASan, UBSan, fuzz-build, coverage, valgrind).
-  `dev` has the release commit plus later doc-only merges (a README refresh and
-  this handoff).
-- **Release PR #284 (`dev` -> `main`)** open, CI green (run 553).
-  `main` is protected: it needs review/approval to merge.
-  https://gitea.tap-tap.win/TapTap/FastSync/pulls/284
-- **`PROTOCOL_VERSION` = `"2.27.0"`** (`src/shared/config.h`); CMake
-  `project(FastFileTransfer VERSION 2.27.0)`.
-- Working tree clean; no wave worktrees remain.
+- **rsync-parity tracks 1-6 landed on `dev`** via **PR #303** (`10159dc`,
+  "feat(parity): rsync parity tracks 1-6 (protocol 2.28.0)"). Dev push CI run
+  **581** fully green: lint, build-and-test, parity-full, ASan, UBSan,
+  fuzz-build, coverage, valgrind.
+- **`PROTOCOL_VERSION` = `"2.28.0"`** (`src/shared/config.h`); CMake
+  `project(FastFileTransfer VERSION 2.28.0)`. The cycle batched all wire
+  changes (stats counters, filter-rule block, `--verify-basis`) under the one
+  bump.
+- **`main` = `ef76c90`** (tag `v2.26.0`); the 2.27.0/2.28.0 work is on `dev`
+  and not yet released. A `dev -> main` v2.28.0 release PR is the next step.
+- Parity matrix: **116 ✅ / 14 ⚠️ / 27 ❌ = 157** (was 111/13/33 at cycle start).
+- Working tree clean; feature branch deleted; no scratch trees or worktrees.
+
 
 ## What landed this session
 1. **Wave 8 (refactors):** Config X-macro wire table; single-owner `authorized_root`;
@@ -52,9 +55,10 @@
    `tests/test_config.c`). Two residuals were reclassified **divergent**: `-M`
    over daemon/TCP (no argv channel in FastSync's binary config handshake;
    rsync-daemon differential pins the rsync behavior) and receiver-side
-   `protect`/`risk` re-derivation for destination-only entries (would need a
-   receiver filter engine; differential pins the divergence). The options pass
-   stands at **110 ✅ / 21 ⚠️ / 26 ❌**. New `tests/integration/test_option_parity.py`
+    `protect`/`risk` re-derivation for destination-only entries (would need a
+    receiver filter engine; differential pins the divergence — **reversed by
+    track 4a below**, which adds that engine). The options pass
+    stands at **110 ✅ / 21 ⚠️ / 26 ❌**. New `tests/integration/test_option_parity.py`
    holds the rsync differentials (bwlimit parse+rate, info lines, real-setpriv
    `--ignore-errors`, rsync-daemon `-M`, filter-protect pin).
 
@@ -74,7 +78,8 @@
    heuristic with a 10× size window, not rsync's matcher), but its residual is the
    candidate-selection heuristic itself: the final tree is byte-exact by design, so
    it is pinned by the `TestFuzzy` threshold suite rather than a byte-level rsync
-   differential. The parity-review pass then moved `--delete-delay` to ⚠️ (the
+   differential. (Track 5b later found the name heuristic is rsync's own and moved
+   the row ❌ → ⚠️, leaving only the narrower delta size window; see entry 15.) The parity-review pass then moved `--delete-delay` to ⚠️ (the
    plan-time `--max-delete` charge and non-recursive deferred removal differ from
    rsync when a snapshotted entry fails removal). Differential-gate allowlist
    entries `min_size`/`empty_dirs_recursive`/`dirs_plain` were removed. The
@@ -85,7 +90,8 @@
     `-n --delete` now sends the same filter-excluded + size-pruned protected
     prefixes and synchronized-directory scope as a real run (dry-run would-delete
     matches rsync for source-derived protections; the destination-only exclude
-    residual and readdir ordering remain); `--delete-delay` now charges
+    residual was later closed by track 4a, readdir ordering remains);
+    `--delete-delay` now charges
     `--max-delete` on actual removals and re-scans a queued directory at commit
     to remove content created after the plan, with an independent deferred-list
     cap (only partial-delete ordering remains); and `--info=name2` emits `NAME is
@@ -110,6 +116,85 @@
     caveats, so the row stays ⚠️ and the matrix is unchanged at
     **111 ✅ / 14 ⚠️ / 32 ❌ = 157**.
 
+13. **Wire parity track 4a** on `feat/parity-2.28` (`PROTOCOL_VERSION` stays
+    `2.28.0`): the receiver now has a delete-time filter engine. The sender
+    compiles its root-level selection rules exactly as the scanner does
+    (`filter_base_build`) and streams them as one bounded, self-describing
+    config-frame block (action, sides, anchored, dir-only, negate, owner,
+    pattern; bounded rule count and pattern bytes, unknown action/sides is a
+    protocol error). The receiver reconstructs `protect_rules` and applies them
+    first-match-wins to each extraneous destination path in every delete timing
+    (the whole-tree commit walker, the `--delete-during`/`--delete-delay`
+    per-directory plans, and the `-n` would-delete enumeration), so a
+    `P *.log` rule protects a destination-only `extra.log` like rsync (with
+    `risk` cancelling); the sender-derived protected-prefix behavior is
+    preserved when no rules are sent and `--delete-excluded` semantics are
+    unchanged. Per-directory merge (`:`/`.`) receiver re-derivation remains the
+    residual. `TestFilterProtect` (real + dry-run) plus differential cases
+    `filter_protect`, `filter_protect_during`, `filter_protect_delay` added and
+    the `--filter=RULE` row moves ❌ → ✅: matrix now
+    **115 ✅ / 11 ⚠️ / 31 ❌ = 157**; unit tests, the three named integration
+    files, clang-format and cppcheck clean.
+
+14. **Wire parity track 5a** on `feat/parity-2.28` (`PROTOCOL_VERSION` stays
+    `2.28.0` by project decision): the three basis-dir options now default to
+    rsync's metadata quick-check (equal size + equal mtime, or size alone under
+    `--size-only`; `-I` disables matching) instead of FastSync's historical
+    xxHash64 content equality, so a same-size/different-content basis is trusted
+    exactly as rsync trusts it. A new FastSync-only, long-only `--verify-basis`
+    flag restores the strict whole-file content equality; its bool is appended to
+    the basis block of the config frame (golden wire frame 882 → 886 bytes).
+    `--verify-basis` streams the confined basis descriptor to hash it, and a
+    basis hit is no longer capped at the 256 MiB whole-file payload bound:
+    `--copy-dest` streams the basis through a bounded buffer and `--link-dest`'s
+    copy fallback streams from the basis, so an over-limit hit materializes (a
+    basis MISS still falls back to the normal transfer and keeps its own bound).
+    A `--copy-dest` hit re-applies the SOURCE attributes (the sender transmits
+    the source metadata with the basis check frame), matching rsync's
+    "copy then fix attributes"; a `--link-dest` success keeps the shared inode's
+    attributes (writing through it would mutate the basis). Differential cases
+    `copy_dest` and `verify_basis` added; `test_basis_dir_size_only_content_residual`
+    converted to a passing parity assertion; `TestBasisDestDirs` updated for the
+    new default + `--verify-basis`; unit tests cover the quick-check/verify
+    decision and the same-size/different-content handshake. The
+    `--compare-dest`/`--copy-dest`/`--link-dest` rows move ❌ → ⚠️ (relative-DIR
+    resolution base and over-limit MISS refusal): matrix now
+    **116 ✅ / 13 ⚠️ / 28 ❌ = 157**.
+
+15. **No-wire parity track 5b** on `feat/parity-2.28` (`PROTOCOL_VERSION` stays
+    `2.28.0` by project decision): `-y`/`--fuzzy` reclassified ❌ → ⚠️. A probe
+    against real rsync 3.4.1 (pinned `-B8192`, repeated-content 64 KiB corpus)
+    showed the name heuristic is already rsync's (`util1.c fuzzy_distance` /
+    `find_filename_suffix` + the exact size+mtime pass) and the output is always
+    byte-exact; the only residual is candidate ELIGIBILITY, because FastSync's
+    `delta_should_attempt` gate caps the size ratio at 10× and requires both
+    files ≥ 16 KiB while rsync will reuse a basis from 0.25× to 10000× and below
+    16 KiB. The choice is observable only as `--stats` bandwidth counters. Added
+    differential case `fuzzy_basis` (same-suffix sibling, one name edit,
+    identical content, block size pinned) asserting tree **and** normalized
+    `--stats` parity where the choices coincide, plus `TestFuzzy` pinning the
+    window boundary on both sides (>10× and <16 KiB siblings declined by
+    FastSync while rsync uses them, both trees byte-identical). Matrix now
+    **116 ✅ / 14 ⚠️ / 27 ❌ = 157**.
+
+16. **Lockstep delete-default track 6** on `feat/parity-2.28` (`PROTOCOL_VERSION`
+    stays `2.28.0`): plain `--delete` now defaults to rsync's delete-during
+    (`--del`) timing, normalized on the client onto the existing `delete_during`
+    wire bool. The old late whole-tree commit is opt-in via `--delete-after` or
+    the FastSync-only long `--delete-commit` (identical `delete_after` timing).
+    `-d/--dirs` still falls back to the end commit, `--delay-updates` still
+    deletes before publication, and `--files-from`/`-R` scope is unchanged. The
+    `STATUS_DELETE_PLAN` frame gained a one-int `apply` flag so the per-run
+    config block (including `--delete-missing-args` exact paths) is always
+    transmitted, on a config-only carrier when the scope allows no directory
+    plan — fixing a latent bug with a file-only `--files-from` list. Differential
+    cases `delete`/`delete_commit`/`filter_protect_after` plus the extended
+    `test_delete_timing_parity.py` (plain `--delete` mid-abort removes reached
+    extras, `--delete-commit` defers) pass; full `-m "not setpriv"` suite,
+    clang-format and cppcheck clean. Matrix unchanged at
+    **116 ✅ / 14 ⚠️ / 27 ❌ = 157** (the `--delete`/`--delete-during` rows stay
+    ⚠️ for the abort boundary; `--delete-after` stays ✅).
+
 ## Next steps
 1. **Merge PR #284** (`dev` -> `main`) once reviewed (protected branch).
 2. **Deferred security items** (documented, not implemented):

README.md

@@ -113,9 +113,11 @@ matrix is classified as parity, caveat, or divergent in
   (`-B1000`, `-essh`, `-MOPT`, `--opt=value`) are accepted, matching rsync.
 - `-r`, `-b`, `-L`, and `-B` are parsed with the rsync short names.
 - `--stats` prints the counters FastSync can observe plus the receiver-only
-  counters (`Matched data`, deleted files) reported over the wire; rsync's
-  per-type `Number of files` breakdown is not reproduced. `--progress` prints
-  rsync-style per-file blocks (without rsync's leading `./` line).
+  counters reported over the wire (`Matched data`, deleted files, and the
+  created/literal counters); `Number of files` and `Number of created files`
+  carry rsync's per-type breakdown. `--progress` prints rsync-style per-file
+  blocks including the leading `./` line, and (when progress is requested) a
+  paths-only pre-count supplies rsync's `to-chk` denominator.
 - Codecs match rsync 3.4.1: `zstd`/`lz4`/`zlib`/`zlibx` compression and
   `xxh128`/`xxh3`/`xxh64`/`md5`/`md4`/`sha1`/`none` checksums. `auto` honors
   `RSYNC_COMPRESS_LIST`/`RSYNC_CHECKSUM_LIST` and otherwise follows rsync's
@@ -205,11 +207,13 @@ This produces `./build/client` and `./build/server`. `compile_commands.json` is
 | `--compare-dest <dir>` | Extra comparison basis: unchanged files are not transferred (requires/implies `--incremental`) |
 | `--copy-dest <dir>` | Like `--compare-dest`, but copies the unchanged file from DIR into the destination |
 | `--link-dest <dir>` | Like `--copy-dest`, but hard-links the unchanged file from DIR (repeatable; earlier DIRs win) |
-| `--delete` | Delete files on receiver not present in source (default timing: delete-after, i.e. only after the whole transfer succeeded). Scoped to the synchronized directories, so `--files-from` subsets are safe |
+| `--verify-basis` | FastSync-only: require a basis hit (`--compare-dest`/`--copy-dest`/`--link-dest`) to match the source by whole-file digest instead of trusting the size+mtime quick-check (default matches rsync) |
+| `--delete` | Delete files on receiver not present in source (default timing: delete-during, matching rsync, so destination space is freed progressively). Scoped to the synchronized directories, so `--files-from` subsets are safe |
 | `--delete-before` | Delete extras before the transfer starts (implies `--delete`) |
 | `--delete-during`, `--del` | Delete extras once the keep-set is known, before data is applied (implies `--delete`) |
 | `--delete-delay` | Delete extras only after a successful transfer (implies `--delete`) |
 | `--delete-after` | Explicit delete-after timing (implies `--delete`) |
+| `--delete-commit` | FastSync-only: keep the pre-2.28 atomic timing — delete only after the whole transfer succeeded (identical timing to `--delete-after`) |
 | `--delete-excluded` | Also delete filter-excluded destination mirrors (size-pruned mirrors stay protected) |
 | `--max-delete <n>` | Delete at most n destination entries; the rest are skipped and the run exits 25 (partial), matching rsync |
 | `--delay-updates` | Put updated files into place only at the end of the transfer (`--force` is honored at publication) |
@@ -567,6 +571,7 @@ remote SSH argv is already built injection-safe.
 | `--compare-dest <dir>` | Extra comparison basis: unchanged files are not transferred (requires/implies `--incremental`). |
 | `--copy-dest <dir>` | Like `--compare-dest`, but copies the unchanged file from DIR into the destination. |
 | `--link-dest <dir>` | Like `--copy-dest`, but hard-links the unchanged file from DIR (repeatable; earlier DIRs win). |
+| `--verify-basis` | FastSync-only: require a basis hit to match the source by whole-file digest instead of trusting the size+mtime quick-check (default matches rsync). |
 | `--preallocate` | Allocate destination file space up front (fail-fast on a full disk). |
 | `--append` | Resume a shorter destination by appending only its tail (prefix not verified; requires `--incremental`). |
 | `--append-verify` | Like `--append`, but verifies the retained prefix checksum first (falls back to a full transfer on mismatch). |
@@ -574,6 +579,7 @@ remote SSH argv is already built injection-safe.
 | `--delete-before` | Delete extras before the transfer starts (implies `--delete`). |
 | `--delete-during`, `--del` | Delete extras once the keep-set manifest is known, before data is applied (implies `--delete`; early mode, same engine behaviour as `--delete-before`). |
 | `--delete-delay` | Delete extras only after a successful transfer (implies `--delete`; commit mode, same behaviour as `--delete-after`). |
+| `--delete-commit` | FastSync-only: atomic delete-after timing (only after the whole transfer succeeded). |
 | `--delete-after` | Explicit delete-after timing: delete only after the transfer succeeded (implies `--delete`). |
 | `--delete-excluded` | Also delete filter-excluded destination mirrors (size-pruned mirrors stay protected). |
 | `--max-delete <n>` | Delete at most n destination entries; the rest are skipped and the run exits 25 (partial), matching rsync. |
@@ -792,7 +798,7 @@ before the module list, before authentication, and the connecting peer address
 
 ## Protocol and Security
 
-FastSync protocol version `2.27.0` is shared by the client and server. The
+FastSync protocol version `2.28.0` is shared by the client and server. The
 current protocol is sender-driven and includes configuration negotiation,
 including the maximum allocation limit, incremental checks, checksums,
 manifests, keep-alives, abort handling, per-file remove-source results, and

RSYNC_COMPAT.md

@@ -6,9 +6,9 @@ This document maps rsync's full feature set to FastSync's current implementation
 
 | Status | Count | Description |
 |--------|-------|-------------|
-| ✅ Parity | 113 | Reproduces rsync's semantics for this option's scope |
-| ⚠️ Caveat | 12 | Wired and tested, but carries a documented behavioral difference from rsync (named in the row and/or the wave notes) |
-| ❌ Divergent | 32 | Rejected, an accepted no-op, deliberately non-rsync (native config/auth/batch, privileged namespaces, safe-subset privilege), or impossible on any portable filesystem call |
+| ✅ Parity | 116 | Reproduces rsync's semantics for this option's scope |
+| ⚠️ Caveat | 14 | Wired and tested, but carries a documented behavioral difference from rsync (named in the row and/or the wave notes) |
+| ❌ Divergent | 27 | Rejected, an accepted no-op, deliberately non-rsync (native config/auth/batch, privileged namespaces, safe-subset privilege), or impossible on any portable filesystem call |
 | **Total** | **157** | One row per rsync option/feature group; a row may name several spellings |
 
 This matrix reports honest rsync parity, not "implemented" as a synonym for
@@ -32,17 +32,29 @@ that map to a FastSync event (`name`, `flist`, `del`, `remove`, `nonreg`,
 genuinely non-interoperable residuals are reclassified divergent (`-M` over a
 daemon/TCP connection, which FastSync's binary config handshake has no argv
 channel for, and receiver-side `protect`/`risk` re-derivation for
-destination-only entries, which would need a receiver filter engine). After the
+destination-only entries, which would need a receiver filter engine; the
+latter was later implemented in parity track 4a below, so only `-M` over a
+daemon remains divergent). After the
 combined `fix/parity-stats` + `fix/parity-options` + `fix/parity-fs` passes (and
 the later `fix/parity-review` correction that moved `--delete-delay` to ⚠️) the
 matrix is **111 ✅ / 13 ⚠️ / 33 ❌ = 157**.
 
-**Parity track 1 (no-wire, on `feat/parity-2.28`).** Three residual burn-downs that required no protocol change: (1) `-n --delete` now propagates the filter-excluded and size-pruned protected prefixes (and the synchronized-directory scope) into the dry-run keep-set manifest, so its would-delete report matches rsync for source-derived protections and no longer lists the file merely being updated (the destination-only exclude/filter residual and readdir ordering remain, leaving the row ⚠️); (2) `--delete-delay` now charges `--max-delete` on actual removals and re-scans a queued directory at commit to remove content created after the plan, with an independent cap bounding the deferred list and the row's prior caveat closed (ordering of partial removals remains, leaving the row ⚠️); and (3) `--info=name2` now emits `NAME is uptodate` and `--info=name` emits the leading `./` root name line (only the root-line trigger condition and the receiver-side `skip` wording remain, leaving the row ⚠️). The matrix is now **111 ✅ / 14 ⚠️ / 32 ❌ = 157**.
+**Parity track 1 (no-wire, on `feat/parity-2.28`).** Three residual burn-downs that required no protocol change: (1) `-n --delete` now propagates the filter-excluded and size-pruned protected prefixes (and the synchronized-directory scope) into the dry-run keep-set manifest, so its would-delete report matches rsync for source-derived protections and no longer lists the file merely being updated (the destination-only exclude/filter residual was closed by track 4a below; readdir ordering remains, leaving the row ⚠️); (2) `--delete-delay` now charges `--max-delete` on actual removals and re-scans a queued directory at commit to remove content created after the plan, with an independent cap bounding the deferred list and the row's prior caveat closed (ordering of partial removals remains, leaving the row ⚠️); and (3) `--info=name2` now emits `NAME is uptodate` and `--info=name` emits the leading `./` root name line (only the root-line trigger condition and the receiver-side `skip` wording remain, leaving the row ⚠️). The matrix is now **111 ✅ / 14 ⚠️ / 32 ❌ = 157**.
 
 **Parity track 2b (no-wire, on `feat/parity-2.28`).** An opt-in, paths-only metadata pre-count for `--progress`/`-P`/`--info=progress` (only when not `--quiet`) now gives the `to-chk` denominator rsync's full file-list total (every regular file, directory, symlink and special plus the transfer root) and emits the per-directory/symlink/special name lines, in both the sequential and `--threads` paths; `--delete-during`/`--delete-delay` reuse their keep-set pre-scan so no second walk happens, and non-progress runs are unaffected. A fresh multi-directory differential against rsync 3.4.1 matches the name set and the `to-chk` denominator, while a single-file transfer stays byte-identical; the remaining caveats are emission order (rsync's sorted depth-first vs FastSync's readdir/BFS stream, so the `to-chk` numerator and interleaving differ) and re-run/receiver-state-driven over-naming (unconditional `./`, ancestor dirs emitted with a transferred child, and no quick-check for symlinks/empty dirs), keeping the row ⚠️. The matrix is unchanged at **111 ✅ / 14 ⚠️ / 32 ❌ = 157**.
 
 **Parity track 3a (no-wire, on `feat/parity-2.28`).** Three codec refinements, none of which change the wire layout (`PROTOCOL_VERSION` stays 2.28.0): (1) an omitted `--compress-level` now resolves to rsync 3.4.1's per-codec default (zstd 3, zlib/zlibx 6, lz4 ignored) and an explicit level is clamped per codec (zstd 1-22, zlib/zlibx 1-9), verified against `rsync --debug=NSTR1`; (2) `auto` now honors `RSYNC_COMPRESS_LIST`/`RSYNC_CHECKSUM_LIST` (rsync's whitespace-separated preference syntax, unknown names skipped, first supported wins, all-unknown is exit 4) before the compiled-in order, with an explicit `--zc`/`--cc` still winning; and (3) `--compress-choice=zlibx` is reclassified out of the caveat list — FastSync's zlib stream already carries only the literal/delta bytes (rsync's zlibx semantics) and is observably identical to `--zc=zlib`, so the zlib/zlibx aliasing is only an implementation detail. The matrix is now **113 ✅ / 12 ⚠️ / 32 ❌ = 157**.
 
+**Parity track 3b (no-wire, on `feat/parity-2.28`).** `--checksum-choice`/`--cc` is reclassified out of the caveat list: its only documented residual was the delta BLOCK strong checksum (rsync applies the negotiated algorithm there; FastSync keeps a fixed xxHash32, `DeltaBlockSig`). A pre-seeded delta-transfer differential against rsync 3.4.1 (probe: `--no-whole-file -B8192 --stats --out-format=%c|%C %n` for rsync vs `--incremental --delta` for FastSync) shows the choice is **not observable** in the surface the parity gate compares — across `xxh64`/`xxh128`/`xxh3`/`md5`/`md4`/`sha1` and both two-name orders the destination tree is byte-identical, the `Matched data`/`Literal data`/`Total transferred file size` counters are unchanged (and, with the block size pinned, equal to rsync's), the `%c` block-checksum token is invariant, and the exit code is 0. The negotiated algorithm is only visible in `%C`, which renders the whole-file transfer digest and is already byte-identical to rsync. No wire field is added (`PROTOCOL_VERSION` stays 2.28.0). The matrix is now **114 ✅ / 11 ⚠️ / 32 ❌ = 157**.
+
+**Parity track 4a (wire, on `feat/parity-2.28`; `PROTOCOL_VERSION` stays 2.28.0).** The receiver now has a filter engine for deletion: the sender compiles its root-level selection rules exactly as the scanner does (`filter_base_build`, covering `--filter`/`-f`, `--exclude`/`--include`, `-C` and the `protect`/`risk`/`hide`/`show` words) and streams them as one bounded, self-describing block appended to the config frame (per rule: action, sides, anchored, dir-only, negate, owner, pattern; strictly validated with a bounded rule count and total pattern+owner bytes, and an unknown action/sides is a protocol error). The receiver reconstructs `protect_rules` and evaluates them first-match-wins against each extraneous destination path in every delete timing — the whole-tree commit walker (plain `--delete`/`--delete-before`/`--delete-after`), the `--delete-during`/`--delete-delay` per-directory plans, and the `-n` would-delete enumeration — so a `protect`/`P` rule now shields a DESTINATION-ONLY entry that never appeared on the sender, with `risk`/`R` cancelling. The existing sender-derived protected-prefix behavior is preserved when no rules are sent (and for source-derived protections), and `--delete-excluded` semantics are unchanged. Per-directory merge (`:`/`.`) receiver-side re-derivation is the remaining residual: those rules are still enforced only through the sender-derived protected prefixes, so a destination-only entry matching ONLY a per-directory merge rule is not yet shielded (the `-F` row keeps this documented). Differential-tested against rsync 3.4.1: `filter_protect`, `filter_protect_during`, `filter_protect_delay` (`-a --delete[-during|-delay] --filter='P *.log'` over seeded destination-only `.log` extras) plus a FastSync regression test for the dry-run would-delete enumeration (`TestFilterProtect`). The `--filter=RULE` row moves ❌ → ✅. The matrix is now **115 ✅ / 11 ⚠️ / 31 ❌ = 157**.
+
+**Parity track 5a (wire, on `feat/parity-2.28`; `PROTOCOL_VERSION` stays 2.28.0 by project decision).** The three basis-dir options (`--compare-dest`/`--copy-dest`/`--link-dest`) now default to rsync's metadata quick-check instead of FastSync's historical xxHash64 content equality: a basis hit is accepted on equal size plus equal mtime (or size alone under `--size-only`; `-I` disables matching), so a same-size/different-content basis is trusted exactly as rsync trusts it. A new FastSync-only, long-only `--verify-basis` flag restores the stricter whole-file content equality, and its bool is appended to the basis block of the config frame (the golden wire frame grew by one int to 886 bytes; still 2.28.0). `--verify-basis` hashes the basis by streaming its confined descriptor, so an arbitrarily large basis is verified without buffering. Basis materialization is also no longer capped at the 256 MiB whole-file payload bound: a `--copy-dest` hit streams the basis through a bounded buffer, a `--link-dest` copy fallback streams from the basis, and a hit of any size is materialized (a basis MISS still falls back to the normal transfer, which keeps its own bound). A `--copy-dest` hit re-applies the SOURCE attributes (the sender now transmits the source metadata with the basis check frame), matching rsync's "copy then fix attributes"; a `--link-dest` success keeps the shared inode's own attributes exactly as before (writing through the shared inode would mutate the basis). The `--compare-dest`/`--copy-dest`/`--link-dest` rows move ❌ → ⚠️ (residuals: the relative-DIR resolution base and the over-limit MISS refusal). The matrix is now **116 ✅ / 13 ⚠️ / 28 ❌ = 157**.
+
+**Parity track 5b (no-wire, on `feat/parity-2.28`; `PROTOCOL_VERSION` stays 2.28.0 by project decision).** `-y`/`--fuzzy` is reclassified ❌ → ⚠️: the receiver-side similar-file basis is an internal bandwidth optimization (the config `fuzzy` bool over the existing receiver-driven delta handshake, unchanged since 2.9.0), and the transferred tree is byte-exact by design regardless of which basis — or no basis — is chosen. A probe against real rsync 3.4.1 showed the remaining difference is not the name rule (FastSync already ports `util1.c fuzzy_distance`/`find_filename_suffix` plus the exact size+mtime pass) but candidate ELIGIBILITY: rsync will pick a fuzzy basis whose size ratio to the source is unrestricted (empirically from 0.25× to 10000×, and for files as small as 300 B), while FastSync's `delta_should_attempt` gate caps the ratio at 10× and requires both files ≥ 16 KiB, so an out-of-window sibling is declined and the file is sent whole. The choice is observable only as bandwidth (`Matched data`/`Literal data`/`Total transferred file size` in `--stats`); the destination tree and exit code are identical either way. A new differential case (`fuzzy_basis`: same-suffix sibling one name-edit away, content identical, block size pinned to 8192) asserts tree **and** normalized `--stats` parity where the two tools' choices coincide; `TestFuzzy` pins the window boundary on both sides (a >10× and a <16 KiB sibling are declined by FastSync while rsync uses them, both trees byte-identical). No wire field changed. The matrix is now **116 ✅ / 14 ⚠️ / 27 ❌ = 157**.
+
+**Lockstep track 6 (delete default; `PROTOCOL_VERSION` stays 2.28.0).** Plain `--delete` with no explicit timing flag now defaults to rsync's delete-during (`--del`) timing: the client normalizes it onto the existing `delete_during` wire bool in `cli_finalize_config`, so no config-frame field was added, and a tight destination no longer has to hold the whole old+new tree at once (the old atomic commit could hit `ENOSPC`). The old late whole-tree commit is opt-in via `--delete-after` or the FastSync-only long spelling `--delete-commit`, which selects the identical `delete_after` timing (documented equivalence). Precedence is unchanged and order-independent: each timing flag implies `--delete`, at most one timing flag may be given, and a timing flag with `--no-delete` is rejected. `-d/--dirs` still falls back to the end commit; `--delay-updates` still deletes genuine extras before publication (the per-directory skip list protects the staging dir); `--files-from`/`-R` scope is unchanged. The per-directory `STATUS_DELETE_PLAN` frame gained a one-int `apply` flag (still 2.28.0): the one-shot per-run config block (protected prefixes, size-pruned mirrors, `--delete-missing-args` exact paths) is now always sent first on a config-only carrier with `apply=false`, fixing a latent bug where a `--delete-missing-args` run whose `--files-from` list synchronized no directory never transmitted its exact deletions. Differential evidence: `delete` (plain, vs rsync's default), `delete_commit` (FastSync `--delete-commit` vs rsync `--delete-after`), and `filter_protect_after` (whole-tree protect) cases; `TestDeleteTimingFinalStateParity` compares plain `--delete`/`--delete-commit` against rsync on completed runs, and `TestDeleteTimingFailure` proves plain `--delete` removes reached extras on a mid-transfer abort while `--delete-commit` removes nothing. The matrix is unchanged at **116 ✅ / 14 ⚠️ / 27 ❌ = 157** (the `--delete`/`--delete-during` rows stay ⚠️ for the abort boundary; `--delete-after` stays ✅).
+
 **Parity completion wave (protocol 2.23.0 → 2.26.0).** This wave closed the
 remaining gaps the rsync-parity wave left open (delete timing, wire counters and
 output, codec breadth, general `-R`/`-d`, the full filter grammar, receiver-side
@@ -103,19 +115,19 @@ Every one of those has an entry below with its remaining caveats.
 |------|-------------------|-----------------|-------|
 | `--exclude-from=FILE` | Read exclude patterns from file | ✅ Parity | Reads patterns from file |
 | `--include-from=FILE` | Read include patterns from file | ✅ Parity | Reads patterns from file |
-| `--filter=RULE` | Add file-filtering rule | ❌ Divergent | The short `-f` **is** bound to `--filter` (the old FastSync sendfile conflict is gone; sendfile is long-only `--sendfile`), and `-f RULE`, `-f=RULE`, `--filter=RULE` and the two-argument form all parse. Protocol 2.26.0 implements rsync's filter grammar: `+`/`-`, `include`/`exclude`, a leading `/` anchor (to the transfer root or a `.rsync-filter` file's directory), a trailing `/` dir-only rule, and the `merge`/`.`, `dir-merge`/`:`, `hide`/`H`, `show`/`S`, `protect`/`P`, `risk`/`R` and `clear`/`!` words, including the `:`/`.` modifiers. First match wins; the filter layer is independent of `--exclude`/`--include`. **Reclassified because the receiver-side `protect`/`risk` semantics cannot be reproduced:** rsync maintains an independent filter engine on the receiver and re-applies every rule to the destination during deletion, so a `P *.log` rule protects a destination-only `extra.log` (differential test vs rsync 3.4.1 pins this). FastSync is sender-derived: its delete protection is the set of source paths the scan actually pruned, so a rule that matches only a destination-only entry is never re-derived and the extra is deleted. Closing this would require shipping the whole (including per-directory merge) filter grammar to, and re-implementing rsync's dual-sided engine on, the receiver — a protocol/architecture change out of proportion to the residual |
+| `--filter=RULE` | Add file-filtering rule | ✅ Parity | The short `-f` **is** bound to `--filter` (the old FastSync sendfile conflict is gone; sendfile is long-only `--sendfile`), and `-f RULE`, `-f=RULE`, `--filter=RULE` and the two-argument form all parse. Protocol 2.26.0 implements rsync's filter grammar: `+`/`-`, `include`/`exclude`, a leading `/` anchor (to the transfer root or a `.rsync-filter` file's directory), a trailing `/` dir-only rule, and the `merge`/`.`, `dir-merge`/`:`, `hide`/`H`, `show`/`S`, `protect`/`P`, `risk`/`R` and `clear`/`!` words, including the `:`/`.` modifiers. First match wins; the filter layer is independent of `--exclude`/`--include`. **Track 4a (protocol 2.28.0) adds the receiver filter engine:** the sender compiles its root-level rules exactly as the scanner does (`filter_base_build`) and streams them as one bounded, self-describing config-frame block; the receiver reconstructs them and re-applies first-match-wins to every extraneous destination path during deletion, so a `P *.log` rule protects a destination-only `extra.log` (differential `filter_protect`/`filter_protect_during`/`filter_protect_delay` vs rsync 3.4.1, plus the `-n` would-delete enumeration) — matching rsync's dual-sided engine for the command-line rule set. **Remaining residual:** per-directory merge (`:`/`.`, and therefore `-F`) is not yet re-derived on the receiver; a destination-only entry that matches ONLY a per-directory merge rule is still protected only through the sender-derived source-mirror prefixes, not by the received base rule list |
 | `--files-from=FILE` | Read source file list from file | ✅ Parity | Entries are paths relative to the source root (leading `./` stripped, `..`/absolute rejected at parse time, blank lines ignored; NUL-delimited with `-0`). A listed regular file is transferred; a listed directory transfers its whole subtree (FastSync recursion is always on). Non-listed paths are pruned by the scanner; the delete manifest is scoped to the listed directory subtrees. A listed entry that does not exist is a hard error unless `--ignore-missing-args`/`--delete-missing-args` is given. **An empty list is a zero-transfer success (exit 0), matching rsync 3.4.1** — the earlier claim that rsync reports "no source files specified" was wrong. Scalability note: `file_list_affects` is O(list size) per scanned entry, so a very large list against a huge tree is quadratic (the documented bound) |
 | `-0`, `--from0` | Delimit *-from files with NULs | ✅ Parity | `--files-from` entries become NUL-delimited; the flag may appear before or after `--files-from` on the command line. NUL mode preserves entry bytes exactly (trailing CR/LF are part of the name; only newline mode trims them) |
 | `--max-size=SIZE` | Skip files larger than SIZE | ✅ Parity | `max_size` in scanner |
 | `--min-size=SIZE` | Skip files smaller than SIZE | ✅ Parity | `min_size` in scanner |
 | `-I`, `--ignore-times` | Don't skip files matching size+time | ✅ Parity | `ignore_times` config field (crosses the wire). Disables the size+mtime quick-check in the `--incremental` per-file handshake and the basis-dir quick-match, forcing the file to be transferred rather than skipped as unchanged. Receiver-side policy: `match_by_metadata` (file_receive.c) is bypassed, so the receiver never replies `STATUS_OK` for a matching size+mtime. Requires `--incremental` to have the handshake to act on (rsync does its quick check by default; FastSync's `-I`/`--size-only`/`--modify-window` only take effect under `--incremental`, exactly like they take effect through the basis check) |
-| `--size-only` | Skip based on size only | ✅ Parity | With `--incremental`, ignores mtime |
+| `--size-only` | Skip based on size only | ✅ Parity | With `--incremental`, ignores mtime. Applies identically to the basis-dir quick-check (track 5a): a same-size basis is a hit on size alone, and under the FastSync-only `--verify-basis` the content digest is still required (size-only drops the mtime leg, never the explicit verify) |
 | `-@`, `--modify-window=NUM` | Mod-time comparison accuracy | ✅ Parity | Whole-second tolerance with nanosecond-aware comparisons |
 | `--existing` | Skip creating new files on receiver | ✅ Parity | Existing destination files continue through normal update handling. The rsync man-page alias `--ignore-non-existing` sets the same flag |
 | `--ignore-existing` | Skip updating existing files | ✅ Parity | `ignore_existing` config field (crosses the wire; receiver-side policy). Protocol 2.26.0 short-circuits in the per-file check **before any payload**: when the destination entry already exists, the receiver answers the skip during the incremental handshake instead of letting the sender stream data that would be discarded, so an existing 4 MiB destination costs only the config/check frames (verified with a counting proxy, matching rsync). The write-time paths (regular, delay-updates-staged, hardlink-sibling, special/device) still return `FILE_SAVE_SKIPPED` without overwriting, and `--backup` is disabled for skipped files. Like rsync, it does not apply to directories/symlinks. Combines with `-j`/`--threads` and `--delay-updates` |
 | `--remove-source-files` | Sender removes regular files after confirmed transfer | ✅ Parity | |
 | `-x`, `--one-file-system` | Do not cross filesystem boundaries | ✅ Parity | Sender scanner captures the root device and does not descend into mount-point crossings (`st_dev` differs). **Protocol 2.23.0 matches rsync's entry emission:** the mount-point directory itself is emitted as a payload-less directory entry (so the destination gets an empty directory) while its contents are skipped; previously the crossing subdirectory was dropped entirely |
-| `-F` | Add the default `.rsync-filter` rules | ✅ Parity | Reads one filter rule per line from each directory's `.rsync-filter` file during traversal and applies it to that directory's subtree; the current directory's rules are evaluated before its ancestors', so deeper files override shallower ones and per-directory files override the command-line `--filter`/`-C` base by default (first match wins). **A single `-F` transfers the `.rsync-filter` files themselves, matching rsync; a repeated `-FF` additionally excludes them** (rsync 3.4.1's `-F`/`-FF` are exactly these two rules, with no `.cvsignore` branch). Unsupported/unparseable rules inside a per-directory file fail the scan with a clear error |
+| `-F` | Add the default `.rsync-filter` rules | ✅ Parity | Reads one filter rule per line from each directory's `.rsync-filter` file during traversal and applies it to that directory's subtree; the current directory's rules are evaluated before its ancestors', so deeper files override shallower ones and per-directory files override the command-line `--filter`/`-C` base by default (first match wins). **A single `-F` transfers the `.rsync-filter` files themselves, matching rsync; a repeated `-FF` additionally excludes them** (rsync 3.4.1's `-F`/`-FF` are exactly these two rules, with no `.cvsignore` branch). Unsupported/unparseable rules inside a per-directory file fail the scan with a clear error. **Residual (track 4a):** per-directory rules are still enforced receiver-side only through the sender-derived source-mirror protected prefixes; the base-rule receiver filter engine does not carry per-directory rules, so a destination-only entry matching ONLY a `.rsync-filter` rule is not yet shielded from `--delete` |
 
 ## 4. Directory Options
 
@@ -144,7 +156,7 @@ Every one of those has an entry below with its remaining caveats.
 
 | Flag | Rsync Description | FastSync Status | Notes |
 |------|-------------------|-----------------|-------|
-| `-n`, `--dry-run` | Trial run with no changes | ⚠️ Caveat | Server-contacting since protocol 2.21.0. The routing predicate `dry_run_targets_server()` selects the server-contacting path for any target a real run would reach over the wire (SSH, daemon `host::module`, explicit `--server-host`/`--server-port`, TLS, source-bind `--address`); the client handshakes with the receiver, which runs the normal read-only per-file check and answers `STATUS_DRY_RUN_TRANSFER`/`STATUS_OK` without mutating anything. Protocol 2.25.0 also reports would-delete lines: with `--delete` the receiver's `STATUS_STATS` carries the extras it would have removed and the client prints rsync-style `*deleting` lines (sequential and `--threads`; control bytes escaped). Dry-run never deletes. **Fixed (no-wire):** the dry-run keep-set manifest now carries the same filter-excluded and size-pruned protected prefixes and synchronized-directory scope a real run sends, and the would-be-transferred entries are in the keep-set, so `-n --delete` lists exactly rsync's extras for source-derived protections — the file merely being updated is kept and an excluded/pruned source entry is protected (`test_dry_run_delete_lines_match_rsync`, differential vs rsync 3.4.1). **Remaining caveat:** a destination-only entry that matches an exclude/filter rule is still reported (and really removed in a real run) because FastSync derives delete protection from the source scan rather than re-applying rules on the receiver — the same divergence as the `--filter` protect row, pinned by `TestOptionParity`; and the would-delete line ordering follows the destination readdir order rather than rsync's reverse-sorted walk (the differential compares the sorted set) |
+| `-n`, `--dry-run` | Trial run with no changes | ⚠️ Caveat | Server-contacting since protocol 2.21.0. The routing predicate `dry_run_targets_server()` selects the server-contacting path for any target a real run would reach over the wire (SSH, daemon `host::module`, explicit `--server-host`/`--server-port`, TLS, source-bind `--address`); the client handshakes with the receiver, which runs the normal read-only per-file check and answers `STATUS_DRY_RUN_TRANSFER`/`STATUS_OK` without mutating anything. Protocol 2.25.0 also reports would-delete lines: with `--delete` the receiver's `STATUS_STATS` carries the extras it would have removed and the client prints rsync-style `*deleting` lines (sequential and `--threads`; control bytes escaped). Dry-run never deletes. **Fixed (no-wire):** the dry-run keep-set manifest now carries the same filter-excluded and size-pruned protected prefixes and synchronized-directory scope a real run sends, and the would-be-transferred entries are in the keep-set, so `-n --delete` lists exactly rsync's extras for source-derived protections — the file merely being updated is kept and an excluded/pruned source entry is protected (`test_dry_run_delete_lines_match_rsync`, differential vs rsync 3.4.1). **Track 4a (protocol 2.28.0):** the received receiver-side `protect`/`risk` rules are also applied to the would-delete enumeration, so a destination-only entry matching a `P` rule is no longer reported (or removed in a real run) — matching rsync (`TestFilterProtect::test_protect_dest_only_dry_run_enumeration`). **Remaining caveat:** the would-delete line ordering follows the destination readdir order rather than rsync's reverse-sorted walk (the differential compares the sorted set) |
 | `-b`, `--backup` | Make backups of overwritten files | ✅ Parity | Backup before overwrite |
 | `--backup-dir=DIR` | Backup directory hierarchy | ✅ Parity | `backup_dir` config field |
 | `--suffix=SUFFIX` | Backup suffix (default ~) | ✅ Parity | `suffix` config field |
@@ -157,12 +169,12 @@ Every one of those has an entry below with its remaining caveats.
 
 | Flag | Rsync Description | FastSync Status | Notes |
 |------|-------------------|-----------------|-------|
-| `--delete` | Delete extraneous files from dest | ⚠️ Caveat | `use_delete` config field. Deletion is always derived from the transmitted keep-set manifest of the paths the sender sent/keeps (never from unchecked input), runs through the symlink-safe walker bounded by `MAX_SERVER_DELETE_COUNT`, and skips the `.fastsync-stage` staging dir under `--delay-updates`. FastSync's default timing when no timing flag is given is **delete-after** (extras are removed only once the whole transfer succeeded) — intentionally NOT rsync's `--del`/delete-during default, to preserve FastSync's commit-style safety. By default the destination mirror of a path the source scan pruned (filter/exclude/size rules) is **protected** from deletion — matching rsync, which does not delete excluded files under `--delete`; `--delete-excluded` opts back into deleting them (see below). Deletion is scoped to the **synchronized directories** sent in the manifest (protocol 2.23.0), so a `--files-from` subset no longer deletes untransmitted paths outside the listed directory subtrees. The walk is bounded: a client `--max-delete=NUM` (or the 100000-entry server bound) makes it **partial** — entries up to the bound are removed, the rest are skipped, and the client exits **25** (`RERR_PARTIAL`), matching rsync, rather than failing the transfer. Extraneous destination symlinks are unlinked by name (never followed); a directory still holding a kept/protected entry is left behind rather than failing |
-| `--delete-before` | Delete before transfer | ⚠️ Caveat | Implies `--delete`. The sender runs a full source pre-scan (paths only) and transmits the keep-set manifest BEFORE any file data; the receiver validates it, removes every destination entry not listed (bounded walk, staging-dir skip, protected prefixes honored), then acks `STATUS_OK`. The sender only starts streaming after the deletion committed, or aborts if the receiver reported a deletion error. By definition the deletions already happened when a later transfer phase fails — rsync's delete-before is destructive the same way; a subsequent failure does not restore the removed files. Divergence: the keep-set is the pre-scan snapshot, so a file that appears on the source between the pre-scan and the data pass is still transferred but was not protected from deletion |
-| `--del`, `--delete-during` | Delete during transfer | ⚠️ Caveat | Both spellings accepted; imply `--delete`. **Protocol 2.24.0 implements per-directory delete plans:** as the sender finishes each source directory it streams a `STATUS_DELETE_PLAN` for that directory and the receiver removes that directory's extras before applying the next directory's data, so a mid-transfer failure has already removed the extras of the directories reached (verified with a byte-slicing proxy). **Remaining divergence:** the exact abort boundary and the progressive ordering of removals versus rsync's generator can differ, and `-d`/`--dirs` (no descent) falls back to the end-of-transfer commit. `-R` plans are scoped to the transferred prefix subtree |
+| `--delete` | Delete extraneous files from dest | ⚠️ Caveat | `use_delete` config field. Deletion is always derived from the keep-set the sender actually transmitted (the per-directory `STATUS_DELETE_PLAN` set by default, or the whole-tree manifest for the late timings — never from unchecked input), runs through the symlink-safe walker bounded by `MAX_SERVER_DELETE_COUNT`, and skips the `.fastsync-stage` staging dir under `--delay-updates`. **Lockstep track 6 (protocol 2.28.0): plain `--delete` with no explicit timing flag now defaults to `--delete-during`**, exactly like rsync's `--del` (the client normalizes it to the existing `delete_during` wire bool; no new wire field). This frees destination space progressively during the transfer and avoids the whole-old+new-tree peak that could `ENOSPC` a tight destination. The old late whole-tree commit is opt-in via `--delete-after` or the FastSync-only long spelling `--delete-commit`. **Caveat (shared with `--delete-during`):** the exact mid-transfer abort boundary can differ from rsync's generator (rsync removes all extras ahead of its throttled sender; FastSync removes only the directories it has reached), `-d/--dirs` falls back to the end-of-transfer commit, and the surviving-set ordering under a partial `--max-delete` can differ — on a completed run the trees agree. By default the destination mirror of a path the source scan pruned (filter/exclude/size rules) is **protected** from deletion — matching rsync, which does not delete excluded files under `--delete`; `--delete-excluded` opts back into deleting them (see below). Deletion is scoped to the **synchronized directories** sent on the wire (protocol 2.23.0), so a `--files-from` subset no longer deletes untransmitted paths outside the listed directory subtrees. The walk is bounded: a client `--max-delete=NUM` (or the 100000-entry server bound) makes it **partial** — entries up to the bound are removed, the rest are skipped, and the client exits **25** (`RERR_PARTIAL`), matching rsync, rather than failing the transfer. Extraneous destination symlinks are unlinked by name (never followed); a directory still holding a kept/protected entry is left behind rather than failing |
+| `--delete-before` | Delete before transfer | ⚠️ Caveat | Implies `--delete`. The sender runs a full source pre-scan (paths only) and transmits the keep-set manifest BEFORE any file data; the receiver validates it, removes every destination entry not listed (bounded walk, staging-dir skip, protected prefixes honored), then acks `STATUS_OK`. The sender only starts streaming after the deletion committed, or aborts if the receiver reported a deletion error. By definition the deletions already happened when a later transfer phase fails — rsync's delete-before is destructive the same way; a subsequent failure does not restore the removed files. **Phase-0 divergence (sharpened):** rsync builds the full file list first, so a source file created after that scan is NOT transferred and its destination extra is deleted; FastSync's single-threaded data pass re-scans the source, so the late file IS transferred (a safe superset), while FastSync `--threads` pipelines the scan and matches rsync |
+| `--del`, `--delete-during` | Delete during transfer | ⚠️ Caveat | Both spellings accepted; imply `--delete`, and since lockstep track 6 this is also the default timing of a plain `--delete`. **Protocol 2.24.0 implements per-directory delete plans:** as the sender reaches each source directory it streams a `STATUS_DELETE_PLAN` for that directory and the receiver removes that directory's extras (verified with a byte-slicing proxy). The one-shot per-run config block (protected prefixes, size-pruned mirrors, `--delete-missing-args` exact paths) rides a dedicated config-only carrier frame with an `apply=false` flag, so it reaches the receiver even when the scope allows no directory plan at all (a `--files-from` list of bare files synchronizes no directory). **Phase-0 divergence (sharpened):** on a mid-transfer abort rsync's generator (which runs ahead of its throttled sender) has already removed ALL the extras it planned, whereas FastSync has removed only the directories it actually reached; on a completed run both agree. Also `-d`/`--dirs` (no descent) falls back to the end-of-transfer whole-tree commit, and the surviving-set ordering under a partial `--max-delete` can differ. `-R` plans are scoped to the transferred prefix subtree |
 | `--delete-delay` | Find deletions during, delete after | ⚠️ Caveat | Implies `--delete`. **Protocol 2.24.0 implements rsync's delete-delay timing:** the sender records each directory's delete plan while scanning and the receiver commits those removals only after the whole transfer succeeds (per plan), so an extra created in the destination after its directory's plan survives while `--delete-after` re-scans and removes it, and a failed transfer removes nothing. The **reported** deleted count advances only on an actual removal. **Fixed (no-wire):** the `--max-delete` budget is now charged on ACTUAL removals (an unlink/rmdir that succeeded), not at plan/snapshot time, and a queued directory is re-scanned at commit and removed recursively (content created after the plan included), matching rsync: a snapshotted entry that fails or is skipped consumes no budget, so a later extra rsync would delete is still deleted. The deferred snapshot list keeps an independent hard cap (`DELETE_PLAN_SERVER_LIMIT`) so it cannot grow without bound now that the budget is no longer charged while scanning. A `--max-delete=2` partial delete reports exactly 2 and exits 25 in both tools, and the refilled-directory differential (late content removed, directory removed, budget shared) now matches rsync 3.4.1 on both sides (`test_delete_delay_budget_parity.py`, `test_delete_timing_parity.py`). Unit tests cover recursive removal, actual-removal charging, and the bounded deferred list. **Caveat:** the exact ordering of which extras are removed first under a partial `--max-delete` can still differ from rsync's generator (the survivor set is compared by count, not identity) |
-| `--delete-after` | Delete after transfer | ✅ Parity | Implies `--delete`. The delete-after timing is also what plain `--delete` does: the keep-set manifest closes the data stream and the receiver commits the bounded deletion only after the terminal `STATUS_FINISHED` proves the whole transfer (every data frame received and stored) succeeded. A failed or aborted transfer removes nothing |
-| `--delete-excluded` | Also delete excluded files | ⚠️ Caveat | `delete_excluded` config field. Under `--delete` FastSync protects (rsync's default) the destination mirror of paths the sender's source scan pruned by the user-selection rules — the `--filter`/`-F`/`-C` layer and the legacy `--exclude`/`--include` layer. The sender transmits those concrete pruned paths as **protected prefixes** in the delete-manifest frame (see the Phase-3 notes below); the walker never descends into or removes them. `--delete-excluded` opts back in: the sender sends an empty protected list, so the excluded destination mirrors become ordinary extras and are removed. **`--max-size`/`--min-size` pruned mirrors are a separate, always-on protection** (protocol 2.23.0, rsync parity): size-pruned source mirrors survive `--delete` even with `--delete-excluded`. Divergences (documented): protection is derived only from what the source scan actually pruned — a stray destination-only file that happens to match an exclude rule is not protected (FastSync never re-applies rules to the destination, keeping deletion sender-derived) |
+| `--delete-after` | Delete after transfer | ✅ Parity | Implies `--delete`. Selects the late whole-tree commit: the keep-set manifest closes the data stream and the receiver commits the bounded deletion only after the terminal `STATUS_FINISHED` proves the whole transfer (every data frame received and stored) succeeded. A failed or aborted transfer removes nothing. Since lockstep track 6 a plain `--delete` defaults to delete-during (rsync's `--del`); `--delete-after` — or the FastSync-only `--delete-commit` spelling, which selects the identical timing — is the explicit way to keep the old commit-style behavior |
+| `--delete-excluded` | Also delete excluded files | ✅ Parity | `delete_excluded` config field. Under `--delete` FastSync protects (rsync's default) the destination mirror of paths the sender's source scan pruned by the user-selection rules — the `--filter`/`-F`/`-C` layer and the legacy `--exclude`/`--include` layer. The sender transmits those concrete pruned paths as **protected prefixes** in the delete-manifest frame (see the Phase-3 notes below); the walker never descends into or removes them. `--delete-excluded` opts back in: the sender sends an empty protected list, so the excluded destination mirrors become ordinary extras and are removed. **`--max-size`/`--min-size` pruned mirrors are a separate, always-on protection** (protocol 2.23.0, rsync parity): size-pruned source mirrors survive `--delete` even with `--delete-excluded`. Track 4a (protocol 2.28.0) additionally re-applies the received `protect`/`risk` rules on the receiver, so a destination-only entry matching an exclude rule is protected (or left at risk) exactly like rsync; the remaining sender-derived `--delete-excluded` behavior (an unqualified rule becomes sender-only, so its source mirror and matching destination-only extras are deleted) is unchanged |
 | `--max-delete=NUM` | Max files to delete | ✅ Parity | `max_delete` config field (default -1 = no client limit; 0 = delete nothing). **Protocol 2.23.0 matches rsync's partial semantics:** the receiver deletes up to NUM entries (regular files, symlinks and empty directories; each directory removal counts as one) and then **stops deleting, skips the rest, and reports the run as partial**. The client prints a "deletions stopped due to `--max-delete` limit" message and exits **25** (rsync's `RERR_PARTIAL`), not a hard failure — the transfer itself succeeded. NUM only applies together with `--delete` (it is inert otherwise, matching rsync). A client NUM below the server hard bound `MAX_SERVER_DELETE_COUNT` (100000) replaces it; a NUM above it never raises that cap. Deleting an entire destination with no limit is still bounded by the server's 100000-entry ceiling. `--delete-missing-args` exact-path deletions and the ordinary extras walk draw from the same budget, matching rsync |
 | `--ignore-errors` | Delete even with I/O errors | ✅ Parity | Sender-side, client-only config field. Matches rsync's semantics exactly: an unreadable source subdirectory is always skipped so the readable tree transfers (the transfer root itself stays fatal), and the run reports rsync's partial-transfer exit **23**. Deletion policy follows rsync: by default an I/O error suppresses deletion (`IO error encountered -- skipping file deletion`), while `--ignore-errors` lets the deletion commit. The decision applies to every timing (`--delete`, `--delete-before`, `--delete-during`, `--delete-delay`, `--delete-after`) in both the sequential and `--threads` send paths. Differential-tested against rsync 3.4.1 with both tools run as an unprivileged user (mode-000 source directory); the reference build's root-only gate still excludes the EACCES differential, but the setpriv differential test exercises it. The piece that stays FastSync-specific is documented under the recursive-empty-directory residual: FastSync never emits an unreadable (or empty) directory entry, so that mirror is an extra that a run with `--ignore-errors` removes, where rsync emits the directory and keeps its mirror |
 | `--force` | Force deletion of non-empty dirs | ✅ Parity | `force_delete` receiver config field (crosses the wire). rsync's `--force` lets an incoming non-directory replace a destination directory; FastSync implements exactly that: when a regular file (or symlink) is written to a path that is currently a (possibly non-empty) destination directory, `--force` removes that directory tree first — confined to the receive root and symlink-safe (O_NOFOLLOW fd walk, symlinks removed by name, never followed) — so the install can place the file. **Protocol 2.23.0 honors `--force` on the `--delay-updates` publication path too**, not only the immediate-install path. Without `--force` such a write fails and the run aborts. Gated by the server `--allow-delete` policy (a client cannot use `--force` to remove a destination tree on a server that forbids deletion) |
@@ -176,8 +188,8 @@ The `STATUS_MANIFEST` frame is count-delimited and position-independent: the
 receiver commits the deletion either when the manifest arrives (early modes:
 `--delete-before`/`--delete-during`, which additionally acknowledge with
 `STATUS_OK` before data flows) or after the terminal `STATUS_FINISHED` proves
-the whole transfer succeeded (commit modes: plain `--delete`/`--delete-after`/
-`--delete-delay`). Timing is chosen purely from the config, so server policy
+the whole transfer succeeded (commit modes: `--delete-after`/`--delete-delay`;
+plain `--delete` joined the per-directory plans in track 6). Timing is chosen purely from the config, so server policy
 (`--allow-delete` off) still disables deletion without deadlocking the early
 manifest ack. `--delete-delay` and `--delete-during` are each implemented as
 the closest safe approximation their engine mode allows; the divergences are
@@ -259,7 +271,10 @@ Flag-conflict policy: unlike rsync's last-one-wins behaviour, every deletion
 timing flag implies `--delete`, and combining a timing flag with `--no-delete`
 (in either argument order) — or more than one timing flag — is rejected as a
 configuration error rather than silently resolved. Note the check is
-order-independent because it runs over the fully parsed config. The deletion
+order-independent because it runs over the fully parsed config. The
+FastSync-only `--delete-commit` is a late-timing spelling (it maps onto
+`--delete-after`), so it conflicts with any different timing flag exactly like
+`--delete-after` does. The deletion
 POLICY flags (`--delete-excluded`, `--max-delete`, `--ignore-errors`, `--force`)
 do NOT imply `--delete`; without `--delete` they are inert (matching rsync).
 
@@ -651,11 +666,11 @@ targets verbatim, matching rsync.
 | Flag | Rsync Description | FastSync Status | Notes |
 |------|-------------------|-----------------|-------|
 | `--checksum` | Skip based on checksum | ✅ Parity | `-c`/`--checksum` compares per-file whole-file content digests to skip unchanged files. **As of protocol 2.23.0 the short `-c` implies the checksum quick-check**, so a plain `-c` run verifies content rather than only affecting the `--incremental` handshake. The digest algorithm is `xxh128` by default (protocol 2.26.0's negotiated default) and is selectable via `--checksum-choice`/`--cc` (`xxh128`/`xxh3`/`xxh64`/`xxhash`/`md5`/`md4`/`sha1`/`none`/`auto`, plus rsync's two-name form) and `--checksum-seed=NUM` (see those rows) |
-| `--checksum-choice=STR`, `--cc=STR` | Choose checksum algorithm | ⚠️ Caveat | Real algorithm selection for the per-file whole-file digest used by the `--incremental`/`--checksum` handshake and basis-dir verification. **Protocol 2.26.0 accepts rsync 3.4.1's full set** — `xxh128` (the negotiated default), `xxh3`, `xxh64`, `xxhash`, `md5`, `md4`, `sha1`, `none`, `auto`, and the two-name `transfer,pre-transfer` form — with rsync's exit-4 rejection of an unknown name and of `none` on the transfer side when `--checksum` is on. `--cc=ALG` and space forms both parse. The algorithm id and seed cross the wire; the receiver hashes its old file with the same algorithm+seed and the per-file `STATUS_CHECK` handshake carries a bounded digest pinned to the negotiated length. `checksum_digest_file` now streams **every** supported algorithm (md4 via the self-contained RFC 1320 code, sha1/md5 via EVP, none as an empty digest), so the streaming path matches its contract, and `--out-format %C` uses the selected **transfer** half of a two-name choice and renders each algorithm byte-for-byte like rsync (xxh128 high-then-low, xxh64/xxh3 big-endian, md5/md4/sha1 standard hex, none a blank 2-char column) — differential-tested across all algorithms. **Remaining divergence:** rsync uses this choice for the block checksum on the wire too, while FastSync selects only the whole-file comparison digest and keeps the delta BLOCK strong checksum at xxHash32. `auto` now consults `RSYNC_CHECKSUM_LIST` (rsync's whitespace-separated preference list; unknown names skipped, first supported wins, all-unknown is exit 4) before the compiled-in order; because both peers run the identical build this deterministic resolution needs no rsync peer probe, and an explicit `--cc` still wins. The list is differential-tested through `--out-format %C` (byte-identical digests to rsync for md5/sha1/xxh3) |
-| `--compare-dest=DIR` | Compare dest files relative to DIR | ❌ Divergent | DIR is a receiver-side basis; protocol 2.26.0 uses an absolute path verbatim (rsync semantics) and resolves a relative path below the destination root (`..` components are rejected, `//` collapsed and trailing `/` dropped). On the receiver's per-file check (implies `--incremental`) an exact match = same size + mtime (unless `--size-only`; `-I` disables matching) **and** equal xxHash64 of the sender's file; a match suppresses the data transfer. compare-dest never copies: it only skips a file the destination does **not** already hold (sparse destination, rsync parity), and is consulted before the normal delta/full paths. Repeatable; searched in command-line order, first match wins. **Reclassified Divergent (differential evidence):** FastSync verifies a basis hit's content with xxHash64 while rsync's `--size-only` quick check trusts size (and mtime) alone, so with a same-size/different-content basis rsync skips/links the *wrong* basis content while FastSync transfers the source — a deliberate safety-stricter behavior that cannot match rsync (see `test_basis_dir_size_only_content_residual` in `tests/integration/test_parity_quickwins.py`). Attribute-only differences on a match are also not re-applied (data is skipped so the sender never sends metadata). Sizing: FastSync's whole-file payload limit is 256 MiB on **every** transfer path (not basis-specific); rsync applies basis dirs to arbitrary sizes, so FastSync refuses a basis run whose source contains a larger file up front with a clear error before any transfer. Wire: a basis-count field is always present on the config frame (protocol 2.9.0, so clients and servers must both be 2.9.0) |
-| `--copy-dest=DIR` | Include copies of unchanged files | ❌ Divergent | Same basis rules as `--compare-dest`, but an exact match materializes a **local copy** of the DIR file into the destination (via the normal atomic temp+rename store path, so `--existing`/`--ignore-existing`/`--update`/`--backup`/`--delay-updates` all still apply) instead of transferring data. Repeatable; command-line order = priority. Content is xxHash64-verified before the copy. **Reclassified Divergent** for the same basis-hit verification divergence as `--compare-dest`: rsync's `--size-only` size/quick-check match rings a same-size/different-content file as unchanged and copies the wrong basis bytes, while FastSync's xxHash verification transfers the source (differential test `test_basis_dir_size_only_content_residual`); a basis-hit also keeps whatever metadata the copy derived from the basis rather than rsync's "copy + fix attributes" in attribute-only cases. Requires `--incremental` (implied); incompatible with `-s`. Wire: protocol 2.9.0 |
-| `--link-dest=DIR` | Hardlink to files when unchanged | ❌ Divergent | Same basis rules as `--copy-dest`, but an exact match installs an atomic **hard link** to the DIR file (temp hard link + rename) so no data or disk space is used; where the link is impossible (basis on another filesystem, filesystem refuses links) it falls back cleanly to a byte-identical local copy, never a corrupt/partial file. `--delay-updates` stages the link and publishes by rename, so the final entry stays a real hard link. Repeatable (searched in command-line order, first match wins). Content is xxHash64-verified before linking. **Reclassified Divergent** for the shared basis-hit divergence: with `--size-only` a same-size/different-content basis is linked by rsync (installing wrong content) but FastSync detects the xxHash mismatch and transfers the source (differential test `test_basis_dir_size_only_content_residual`). Other inherent caveats: protocol 2.26.0 re-links an already up-to-date destination file to the basis; a link keeps the basis inode's own mode/uid/gid and mtime — metadata is never written through the shared inode (that would mutate the basis file), so a later `--inplace` run that rewrites such a destination path **will mutate the basis snapshot** through the shared inode (use `--copy-dest` when the destination must stay independently writable); a `--remove-source-files` source satisfied by a basis dir is treated as skipped and therefore **retained** (never removed); basis dirs are excluded from `--delete`. Requires `--incremental` (implied); incompatible with `-s`. Wire: protocol 2.9.0 |
-| `-y`, `--fuzzy`, `--no-fuzzy` | Find similar file for basis | ❌ Divergent | `-y/--fuzzy` is a pure bandwidth optimization on the existing receiver-driven delta path: when a file must be transferred and the destination holds no usable content at the exact path (file absent, or the destination file is outside the delta engine's size bounds), the receiver searches the SAME destination directory for an existing regular file whose basename is similar to the incoming name and uses it as the delta basis, so the sender transmits only the differences instead of the whole file. The output is always byte-exact regardless of which (or whether any) basis is chosen. Decision location: the receiver performs the candidate search inside `receive_incremental_check` and sends the normal `STATUS_DELTA_SIGNATURE`; the sender never learns the basis was a different file, so no new frame type or sender logic was needed — only the config frame grew a `fuzzy` boolean, so `PROTOCOL_VERSION` was bumped **2.8.0 → 2.9.0** (peers must match). Similarity heuristic (deterministic, simpler than rsync's deliberately-fuzzy matching, and documented precisely): candidates are the target's sibling entries in its destination directory, opened `O_NOFOLLOW`/`AT_SYMLINK_NOFOLLOW` under the confined root (symlinks never followed; nothing outside the destination root is ever read or hashed); dotfiles, directories, the target's own name, and the `.fastsync-stage`/temp scratch names are excluded; like the ordinary delta path, the block signature the receiver transmits is derived from on-disk content it may not otherwise send, so a negotiated `--fuzzy` run exposes the destination's sibling files (at block granularity) to the sender as a known-plaintext oracle — the same information class as the normal delta handshake over the file being replaced; the size gate is the delta engine's own bounds (both files ≥ 16 KiB, ≤ `--delta-max`, ratio ≤ 10×) rather than rsync's ~1.5× size window; protocol 2.26.0 uses a name-distance/suffix heuristic modelled on rsync's plus an exact size+mtime pass, and reads a single best candidate; the exact tie-break order can still differ from rsync's; the directory scan is capped at 4096 entries so a pathological directory cannot stall a transfer. When fuzzy applies: only to files the receiver would otherwise send whole — the destination's own file is always preferred as the delta basis when it exists and fits the delta size bounds, so fuzzy does NOT replace an existing-but-different destination basis; FastSync's 10× delta size-ratio bound means an existing destination file that is too far away in size still lets the fuzzy search run. When no similar candidate exists the transfer falls back to the normal whole-file transfer. rsync-divergence note: rsync's own matching uses a fuzzy name/size rule set; FastSync implements the closest safe deterministic approximation above. Because FastSync's delta machinery is off by default (rsync's is on), `--fuzzy` implies `--incremental` + `--delta` (unless `--whole-file`/`-W` or an explicit `--no-delta` switched delta off, in which case fuzzy is inert — matching rsync where `--whole-file` makes fuzzy irrelevant). Unlike the basis-dir options, `--fuzzy` honors an explicit `--no-incremental` (it does not force the handshake back on); an explicit `--no-incremental` also suppresses the delta implication so no invalid `--delta requires --incremental` config results. `--no-fuzzy` negates it. All surrounding semantics are untouched: a fuzzy-reconstructed file is stored as a normal file, so `--remove-source-files`, itemize/`-i`, `--stats`, `--backup`, `--delay-updates`, `--existing`/`--ignore-existing`/`--update` behave exactly as for a whole-file transfer (the fuzzy delta does not skip the file). **Reclassified Divergent:** because the output is always byte-exact, the residual is the candidate-selection heuristic itself — a deterministic name-distance/suffix rule with a 10× size-ratio window (vs rsync's ~1.5× window), not rsync's deliberately fuzzy matcher, so the chosen basis (and thus the wire bytes) can differ from rsync even though the final tree cannot. The Integration fuzzy suite (`TestFuzzy`) pins FastSync's thresholds (exact-size+mtime pass, name-distance rejection, 10× unsuitable-destination fallback); a bit-identical basis choice is not achievable without porting rsync's matcher |
+| `--checksum-choice=STR`, `--cc=STR` | Choose checksum algorithm | ✅ Parity | Real algorithm selection for the per-file whole-file digest used by the `--incremental`/`--checksum` handshake and basis-dir verification. **Protocol 2.26.0 accepts rsync 3.4.1's full set** — `xxh128` (the negotiated default), `xxh3`, `xxh64`, `xxhash`, `md5`, `md4`, `sha1`, `none`, `auto`, and the two-name `transfer,pre-transfer` form — with rsync's exit-4 rejection of an unknown name and of `none` on the transfer side when `--checksum` is on. `--cc=ALG` and space forms both parse. The algorithm id and seed cross the wire; the receiver hashes its old file with the same algorithm+seed and the per-file `STATUS_CHECK` handshake carries a bounded digest pinned to the negotiated length. `checksum_digest_file` now streams **every** supported algorithm (md4 via the self-contained RFC 1320 code, sha1/md5 via EVP, none as an empty digest), so the streaming path matches its contract, and `--out-format %C` uses the selected **transfer** half of a two-name choice and renders each algorithm byte-for-byte like rsync (xxh128 high-then-low, xxh64/xxh3 big-endian, md5/md4/sha1 standard hex, none a blank 2-char column) — differential-tested across all algorithms. **Track-3b finding — the block-checksum residual is not observable.** rsync applies the choice to the block checksum on its wire too, while FastSync selects only the whole-file comparison digest and keeps the delta BLOCK strong checksum fixed at xxHash32 (`DeltaBlockSig`, `delta_signature_create_seeded`). Because FastSync does not interoperate with rsync on the wire, only the compared surface matters, and a pre-seeded delta differential against rsync 3.4.1 (`--no-whole-file -B8192 --stats --out-format=%c|%C %n` vs `--incremental --delta`) shows the choice does not move it: across `xxh64`, `xxh128`, `xxh3`, `md5`, `md4`, `sha1` and both two-name orders the destination tree is byte-identical, `Matched data`/`Literal data`/`Total transferred file size` are unchanged (and equal to rsync's with the block size pinned), the `%c` block-checksum token is invariant (rsync `16 + 6·ceil(size/block)`, already documented under `--out-format`; FastSync its own basis-read counter), and the exit code is 0. The negotiated algorithm is visible only in `%C`, which applies it to the whole-file transfer digest and matches rsync byte-for-byte. A false block match would require the 4-byte adler32 AND the 4-byte xxHash32 to collide; at the 256 MiB maximum with the 1 KiB minimum block size the expected false matches are ≤2⁻¹⁸, and the choice cannot change this because FastSync's block strong sum is fixed. `auto` now consults `RSYNC_CHECKSUM_LIST` (rsync's whitespace-separated preference list; unknown names skipped, first supported wins, all-unknown is exit 4) before the compiled-in order; because both peers run the identical build this deterministic resolution needs no rsync peer probe, and an explicit `--cc` still wins. The list is differential-tested through `--out-format %C` (byte-identical digests to rsync for md5/sha1/xxh3) |
+| `--compare-dest=DIR` | Compare dest files relative to DIR | ⚠️ Caveat | DIR is a receiver-side basis; protocol 2.26.0 uses an absolute path verbatim (rsync semantics) and resolves a relative path below the destination root (`..` components are rejected, `//` collapsed and trailing `/` dropped) — note rsync resolves a relative DIR against the destination directory while FastSync resolves it below the receive root and appends the mirrored source path, so the same relative spelling addresses a different tree (use an absolute DIR for exact parity). On the receiver's per-file check (implies `--incremental`) an exact match is rsync's metadata quick-check: same size and mtime (unless `--size-only`; `-I` disables matching), with NO content digest required by default (track 5a). A match suppresses the data transfer. The FastSync-only `--verify-basis` restores the stricter whole-file content equality. compare-dest never copies: it only skips a file the destination does **not** already hold (sparse destination, rsync parity), and is consulted before the normal delta/full paths. Repeatable; searched in command-line order, first match wins. Differential-tested against rsync 3.4.1 (`compare_dest`, and `test_verify_basis_restores_strict_content`). Residual: a basis MISS above the 256 MiB whole-file payload bound is refused up front (FastSync's general whole-file limit, not basis-specific); rsync applies basis dirs to arbitrary sizes. Wire: a basis-count field plus the `verify_basis` bool are present on the config frame (protocol 2.9.0/2.28.0) |
+| `--copy-dest=DIR` | Include copies of unchanged files | ⚠️ Caveat | Same basis rules as `--compare-dest`, but an exact match materializes a **local copy** of the DIR file into the destination (via the atomic temp+rename store path, so `--existing`/`--ignore-existing`/`--update`/`--backup`/`--delay-updates` all still apply) instead of transferring data. Track 5a re-applies the SOURCE attributes on the copy (rsync's "copy then fix attributes"): the sender transmits the source metadata with the basis check frame, so the copy's mode/uid/gid/mtime match the source rather than the basis inode (differential `copy_dest` compares modes). The copy streams the basis file through a bounded buffer, so a basis larger than the whole-file payload bound still materializes. Repeatable; command-line order = priority. Requires `--incremental` (implied); incompatible with `-s`. Wire: protocol 2.9.0 |
+| `--link-dest=DIR` | Hardlink to files when unchanged | ⚠️ Caveat | Same basis rules as `--copy-dest`, but an exact match installs an atomic **hard link** to the DIR file (temp hard link + rename) so no data or disk space is used; where the link is impossible (basis on another filesystem, filesystem refuses links) it falls back cleanly to a byte-identical local copy (streamed from the basis, so an over-limit basis still works), never a corrupt/partial file. `--delay-updates` stages the link and publishes by rename, so the final entry stays a real hard link. Repeatable (searched in command-line order, first match wins). Differential-tested against rsync 3.4.1 (`link_dest`). Inherent shared-inode semantics (identical to rsync): a link keeps the basis inode's own mode/uid/gid and mtime — metadata is never written through the shared inode (that would mutate the basis file), so a later `--inplace` run that rewrites such a destination path **will mutate the basis snapshot** through the shared inode (use `--copy-dest` when the destination must stay independently writable); protocol 2.26.0 re-links an already up-to-date destination file to the basis; a `--remove-source-files` source satisfied by a basis dir is treated as skipped and therefore **retained** (never removed); basis dirs are excluded from `--delete`. Residual: a basis MISS above the 256 MiB whole-file payload bound is refused (FastSync's general whole-file limit). Requires `--incremental` (implied); incompatible with `-s`. Wire: protocol 2.9.0 |
+| `-y`, `--fuzzy`, `--no-fuzzy` | Find similar file for basis | ⚠️ Caveat | `-y/--fuzzy` is a pure bandwidth optimization on the existing receiver-driven delta path: when a file must be transferred and the destination holds no usable content at the exact path (file absent, or the destination file is outside the delta engine's size bounds), the receiver searches the SAME destination directory for an existing regular file whose basename is similar to the incoming name and uses it as the delta basis, so the sender transmits only the differences instead of the whole file. The output is always byte-exact regardless of which (or whether any) basis is chosen. Decision location: the receiver performs the candidate search inside `receive_incremental_check` and sends the normal `STATUS_DELTA_SIGNATURE`; the sender never learns the basis was a different file, so no new frame type or sender logic was needed — only the config frame grew a `fuzzy` boolean, so `PROTOCOL_VERSION` was bumped **2.8.0 → 2.9.0** (peers must match). Similarity heuristic (a deterministic port of rsync 3.4.1's matcher — `util1.c` `fuzzy_distance`/`find_filename_suffix` plus `generator.c find_fuzzy`'s exact size+mtime pass — documented precisely): candidates are the target's sibling entries in its destination directory, opened `O_NOFOLLOW`/`AT_SYMLINK_NOFOLLOW` under the confined root (symlinks never followed; nothing outside the destination root is ever read or hashed); dotfiles, directories, the target's own name, and the `.fastsync-stage`/temp scratch names are excluded; like the ordinary delta path, the block signature the receiver transmits is derived from on-disk content it may not otherwise send, so a negotiated `--fuzzy` run exposes the destination's sibling files (at block granularity) to the sender as a known-plaintext oracle — the same information class as the normal delta handshake over the file being replaced; the size gate is the delta engine's own bounds (both files ≥ 16 KiB, ≤ `--delta-max`, ratio ≤ 10×); rsync's fuzzy matcher is not tied to a delta size bound and empirically reuses a basis well outside FastSync's window (a 64 KiB source against a repeated-content sibling from 0.25× to 10000×, and files as small as 300 B), so candidate ELIGIBILITY — and hence the chosen basis — can differ even though the name heuristic is the same; protocol 2.26.0 uses rsync's weighted-Levenshtein name/suffix distance plus an exact size+mtime pass and reads a single best candidate; the tie-break (smallest size gap, then lexical name) is deterministic where rsync leaves equal distances to its file-list order; the directory scan is capped at 4096 entries so a pathological directory cannot stall a transfer. When fuzzy applies: only to files the receiver would otherwise send whole — the destination's own file is always preferred as the delta basis when it exists and fits the delta size bounds, so fuzzy does NOT replace an existing-but-different destination basis; FastSync's 10× delta size-ratio bound means an existing destination file that is too far away in size still lets the fuzzy search run. When no similar candidate exists the transfer falls back to the normal whole-file transfer. rsync-divergence note: the name matching is rsync's own rule; the residual is eligibility bounded by FastSync's delta engine, so no name-matcher port can widen it. Because FastSync's delta machinery is off by default (rsync's is on), `--fuzzy` implies `--incremental` + `--delta` (unless `--whole-file`/`-W` or an explicit `--no-delta` switched delta off, in which case fuzzy is inert — matching rsync where `--whole-file` makes fuzzy irrelevant). Unlike the basis-dir options, `--fuzzy` honors an explicit `--no-incremental` (it does not force the handshake back on); an explicit `--no-incremental` also suppresses the delta implication so no invalid `--delta requires --incremental` config results. `--no-fuzzy` negates it. All surrounding semantics are untouched: a fuzzy-reconstructed file is stored as a normal file, so `--remove-source-files`, itemize/`-i`, `--stats`, `--backup`, `--delay-updates`, `--existing`/`--ignore-existing`/`--update` behave exactly as for a whole-file transfer (the fuzzy delta does not skip the file). **Reclassified Caveat (track 5b):** the output is always byte-exact regardless of the basis, and the name rule is rsync's, so the residual is candidate ELIGIBILITY: FastSync's 10× ratio / 16 KiB delta gates make its size window strictly narrower than rsync's, and when eligibility differs the chosen basis — and therefore the `--stats` `Matched data`/`Literal data`/`Total transferred file size` counters — can differ even though the tree cannot. Where the two tools' choices coincide and the block size is pinned, both the tree and the counters match rsync (differential `fuzzy_basis`); `TestFuzzy` pins the window boundary on both sides (a >10× sibling and a <16 KiB sibling are declined, with a byte-exact whole-file fallbaLine truncated
 
 ## 12. Compression
 
@@ -755,7 +770,7 @@ modes or links.
 | `--stop-after=MINS` | Stop after N minutes | ✅ Parity | Client-only sender stop deadline (Phase 6): computing `--stop-after=MINS` (a positive minute count; 0/negative/garbage rejected) and `--stop-at=TIME` (`HH:MM`, `HH:MM:SS`, or `now+N[smhd]`; a past time stops immediately). The transfer stops ELEGANTLY at the next chunk boundary: everything already fully sent is kept and applied, the run returns 0, and --delete (late/delete-after timing) does NOT wipe the destination — when the scan is cut short the partial keep-set manifest is suppressed with a warning (the delete walk is skipped rather than acting on an incomplete keep-set, so unscanned source mirrors survive). `--delete-before`/`--delete-during` still run their complete pre-scan (which ignores the deadline). Local client-only fields: never serialized into the wire config frame, so no PROTOCOL_VERSION bump. `--stop-after` uses CLOCK_MONOTONIC; `--stop-at` uses the wall clock. Works single-threaded and under `-j`/`--threads` (multithreaded). Divergence: rsync computes `--stop-after` from the run start; FastSync likewise. When both are given, the earlier of the two deadlines wins (checked per iteration). See the Phase-6 stop notes below |
 | `--stop-at=TIME` | Stop at specified time | ✅ Parity | Deadline transfer stop (client-only, never serialized). Protocol 2.26.0 accepts rsync's full date/time grammar (`2030-12-31T23:59`, `2030/12/31T23:59`, `2030-12-31`, `12-31`, `14:00`, `:59`, `1`) in addition to FastSync's `HH:MM[:SS]` and `now+N[smhd]`; a past time stops immediately. Everything already transferred is kept and an early stop suppresses the late `--delete` keep-set so unscanned source mirrors survive. Works single-threaded and under `-j`/`--threads` |
 | `--fsync` | Fsync every written file before publication | ✅ Parity | |
-| `--protocol=NUM` | Force older protocol version | ❌ Divergent | Forces the wire protocol version for this transfer. FastSync has exactly ONE wire format (`PROTOCOL_VERSION`, currently 2.27.0) with no downgrade/backward-compat code paths, so `--protocol=2.27.0` is accepted (it sets the version claim the client sends, which the server already requires to match exactly) and **every other value is rejected up front** with a clear error before any connection — it does not and cannot speak an older or virtual wire format. Divergence from rsync (which negotiates a range and downgrades to an integer 0..31): FastSync's honest contract is force-to-the-one-supported-value; a genuine downgrade would require a per-version compatibility layer that does not exist. Client-only; the server-side exact-match check is unchanged. `--protocol=2.26.0`/`2.25.0`/`2.24.0`/`2.23.0`/`2.22.0`/`2.21.0`/`2.20.0`/`2.19.0`/`2.18.0`/`2.17.0`/`2.16.0`/`2.15.0`/`216`/`31`/garbage are all rejected. See the Phase-6 protocol note below |
+| `--protocol=NUM` | Force older protocol version | ❌ Divergent | Forces the wire protocol version for this transfer. FastSync has exactly ONE wire format (`PROTOCOL_VERSION`, currently 2.28.0) with no downgrade/backward-compat code paths, so `--protocol=2.28.0` is accepted (it sets the version claim the client sends, which the server already requires to match exactly) and **every other value is rejected up front** with a clear error before any connection — it does not and cannot speak an older or virtual wire format. Divergence from rsync (which negotiates a range and downgrades to an integer 0..31): FastSync's honest contract is force-to-the-one-supported-value; a genuine downgrade would require a per-version compatibility layer that does not exist. Client-only; the server-side exact-match check is unchanged. `--protocol=2.27.0`/`2.26.0`/`2.25.0`/`2.24.0`/`2.23.0`/`2.22.0`/`2.21.0`/`2.20.0`/`2.19.0`/`2.18.0`/`2.17.0`/`2.16.0`/`2.15.0`/`216`/`31`/garbage are all rejected. See the Phase-6 protocol note below |
 | `--iconv=CONVERT_SPEC` | Charset conversion | ✅ Parity | Charset conversion of FILE NAMES (not content) at the protocol boundary via iconv(3): `--iconv=LOCAL[,REMOTE]` — the sender converts each local filename LOCAL→REMOTE before transmitting, matching rsync's rule that the spec "stays the same whether you're pushing or pulling": on a PUSH the destination end's charset is the spec's REMOTE half, so the default receiver writes the wire bytes verbatim, and only a server started with its own `--iconv` (the daemon `charset` analog) declares a different destination charset and converts REMOTE→that LOCAL (rsync push parity, differential-tested with and without a server `--iconv`). The full CONVERT_SPEC is serialized into the config frame as a new trailing string field so the peer knows the wire charset; **PROTOCOL_VERSION bumped 2.15.0 → 2.16.0**. `LOCAL[,REMOTE]` parse: single charset ⇒ LOCAL==REMOTE (identity both ways); garbage rejected up front; protocol 2.26.0 additionally accepts `--iconv=.` (the locale's default charset for both directions), `--iconv=-` and `--no-iconv` (disable conversion). Validation probes BOTH directions (a spec that only opens one way is refused, as is a NUL-emitting target charset like utf-16/utf-32/ucs-2, since filenames cannot contain NUL). An unrepresentable name (EILSEQ/EINVAL) fails that path cleanly with a logged `--iconv: cannot convert file name ...` and is never written mangled/truncated. Conversion is applied at EVERY wire-path site (regular/MKDIR/hardlink path+target/symlink path+target/SPECIAL, the delete manifest, the incremental-check path, and the `-s`/`chunk_serialize` embedded blob path), on both client and server (`--iconv` is also a server/daemon option). Zero overhead when unset. See the Phase-6 iconv notes below |
 | `--checksum-seed=NUM` | Set checksum seed | ✅ Parity | Sets the seed for FastSync's whole-file xxHash digest (full 64-bit seed) and for the delta path's per-block xxHash32 strong checksum (low 32 bits of the seed). **As of protocol 2.23.0 a seed of `0` — the default when the flag is unset — is randomized per transfer and the chosen seed is sent to the receiver**, exactly like rsync, so two runs against different content do not share a predictable seed; an explicit non-zero seed is used verbatim, so an explicit seed deterministically reproduces every computed digest on BOTH endpoints (the seed crosses in the config frame). `--checksum-choice=md5` has no seed and ignores it (documented). The value is a strict decimal 0..2⁶⁴-1 (blank, signed, or non-numeric values are rejected). Like rsync, a seed only matters where a digest is actually computed (`--checksum` or a basis-dir run, or a delta transfer); it does not by itself enable `--checksum`/`--delta` |
 | `--secluded-args`, `-s` | Use protocol to send args | ❌ Divergent | Accepted for CLI compatibility (including the rsync short `-s`, Phase 7 Wave A) but a documented **no-op / divergence**. rsync's `-s` protects arguments from shell expansion by shipping them over the protocol; FastSync never passes remote arguments through a shell expansion boundary in the first place — its SSH transport builds the remote argv as **single-quote-escaped shell words** (`ssh_build_remote_command`), so the injection/leak that `-s` guards against does not exist and there is nothing to "seclude". Implementing a true arg-send protocol would mean replacing the argv-based SSH launch with an in-band argument channel, a large redesign of the transport that buys no security here. Chunk serialization remains the long-only `--chunk-serialization`. |
@@ -872,7 +887,7 @@ These are the hardest compatibility items because they require durable formats o
 
 **Phase 6, Wave B (iconv) shipping note (PROTOCOL 2.15.0 → 2.16.0):** `--iconv=LOCAL[,REMOTE]` converts file NAMES at the wire boundary (never content). The full CONVERT_SPEC is serialized into the config frame as a new trailing string field (empty→NULL canonicalized), so both ends share the same wire charset interpretation; this required the PROTOCOL bump because the frame is a strict ordered sequence and a peer that does not parse the new trailing field would desynchronize. Each end derives its charset and the wire charset: the sender opens LOCAL→REMOTE and converts every transmitted filename; on a push the receiver's destination charset is the spec's REMOTE half, so it writes the wire bytes verbatim, unless the server was started with its own `--iconv` naming a different LOCAL charset (then it opens REMOTE→that LOCAL). Conversion is applied at every wire-path site (regular/MKDIR/hardlink path+target/symlink path+target/SPECIAL, the delete manifest keep/protected/missing entries, the incremental-check path, and the embedded `-s`/chunk-blob path). A name it cannot convert (EILSEQ/EINVAL) is failed cleanly with a logged `--iconv: cannot convert file name ...` and is never written truncated/mangled. Validation probes both directions up front (both the sender local→remote and the receiver remote→destination, and, for a server/daemon with its own `--iconv`, the client-REMOTE→server-LOCAL pair) so an unusable spec is rejected before the connection rather than mid-transfer, and NUL-emitting target charsets (utf-16/utf-32/ucs-2) are refused because filenames cannot contain NUL. The wire charset always comes from the sender's REMOTE half; a server whose local charset differs from the client's REMOTE must declare it with its own `--iconv` (the daemon `charset` analog). Conversion is process-global and runs on a single thread per process (sender thread / receiver-loop thread), initialized before worker threads start and freed after they join.
 
-**Phase 6, Wave C (protocol-version) shipping note (no PROTOCOL_VERSION change):** `--protocol=NUM` lets the client force the wire protocol version for a transfer. FastSync's protocol is a single lockstep format: the config frame is a strict ordered sequence and the server requires the client's version string to equal `PROTOCOL_VERSION` exactly (`config_receive_with_validate`, src/shared/config.c) — there are no older-format code paths and no downgrade/negotiation machinery, so a lower/higher/virtual version can never be spoken. The honest contract is therefore: the current `PROTOCOL_VERSION` (2.26.0 as of the parity-completion wave) is accepted and stored into the client's `version` claim (which `config_send` already transmits), and every other value — `2.25.0`, `2.24.0`, `2.23.0`, `2.22.0`, `2.21.0`, `2.20.0`, `2.19.0`, `2.18.0`, `2.18`, `2.17.0`, `2.16.0`, `2.15.0`, `3.0.0`, rsync-integer spellings like `216`/`31`, garbage, empty — is rejected up front in `validate_config()` before any connection, with a clear error that FastSync supports only its current wire protocol and cannot speak an older or virtual one. Implementation is client-only: a server-side `--protocol` is intentionally not added because the server has no negotiation (it only enforces exact match), and it could only ever be the current version. This preserves (and slightly tightens) existing validation: the client now also refuses to launch with a version it cannot actually speak, rather than only the server rejecting it later. A genuine downgrade would require a per-version compatibility layer for every frame/feature added since (append 2.10, preallocate 2.11, hardlinks 2.12, devices/specials/symlink-trust/xattr 2.13, remote-option 2.14, daemon module/auth 2.15, iconv 2.16, dir/symlink times 2.17, privilege flags --super/--copy-as 2.18, SCRAM daemon auth 2.19, packed metadata 2.20, error-detail/dry-run 2.21, preserve-attribute split 2.22, rsync-parity wave 2.23) and is intentionally out of scope — documented divergences from rsync's integer-negotiated downgrade remain.
+**Phase 6, Wave C (protocol-version) shipping note (no PROTOCOL_VERSION change):** `--protocol=NUM` lets the client force the wire protocol version for a transfer. FastSync's protocol is a single lockstep format: the config frame is a strict ordered sequence and the server requires the client's version string to equal `PROTOCOL_VERSION` exactly (`config_receive_with_validate`, src/shared/config.c) — there are no older-format code paths and no downgrade/negotiation machinery, so a lower/higher/virtual version can never be spoken. The honest contract is therefore: the current `PROTOCOL_VERSION` (2.28.0 as of the parity 2.28.0 cycle) is accepted and stored into the client's `version` claim (which `config_send` already transmits), and every other value — `2.25.0`, `2.24.0`, `2.23.0`, `2.22.0`, `2.21.0`, `2.20.0`, `2.19.0`, `2.18.0`, `2.18`, `2.17.0`, `2.16.0`, `2.15.0`, `3.0.0`, rsync-integer spellings like `216`/`31`, garbage, empty — is rejected up front in `validate_config()` before any connection, with a clear error that FastSync supports only its current wire protocol and cannot speak an older or virtual one. Implementation is client-only: a server-side `--protocol` is intentionally not added because the server has no negotiation (it only enforces exact match), and it could only ever be the current version. This preserves (and slightly tightens) existing validation: the client now also refuses to launch with a version it cannot actually speak, rather than only the server rejecting it later. A genuine downgrade would require a per-version compatibility layer for every frame/feature added since (append 2.10, preallocate 2.11, hardlinks 2.12, devices/specials/symlink-trust/xattr 2.13, remote-option 2.14, daemon module/auth 2.15, iconv 2.16, dir/symlink times 2.17, privilege flags --super/--copy-as 2.18, SCRAM daemon auth 2.19, packed metadata 2.20, error-detail/dry-run 2.21, preserve-attribute split 2.22, rsync-parity wave 2.23) and is intentionally out of scope — documented divergences from rsync's integer-negotiated downgrade remain.
 
 **Phase-1/2 selection-and-update status correction (docs):** `-I/--ignore-times`, `--size-only`, `-@/--modify-window`, `--existing`, `--ignore-existing`, `-u/--update`, `-W/--whole-file`, and `--compress-threads` were previously listed as not-implemented in this document but are in fact fully implemented and tested on `dev`. This pass corrects the matrix to match the code. The realistic model of these is that FastSync is a *sender-driven* whole-tree copy, so the size+mtime quick-check and all three receiver-policy skips (`--existing`, `--ignore-existing`, `-u`) are evaluated against the **destination** on the receiver side, and their booleans cross the wire in the config frame. `-I`/`--size-only`/`--modify-window` modify the `--incremental` per-file `STATUS_CHECK` handshake's match predicate (`-I` disables the mtime leg and forces transfer; `--size-only` drops only the mtime leg; `--modify-window` adds tolerance to `metadata_mtime_matches`); they require `--incremental` (or a basis dir) to have a handshake to affect, mirroring how they only matter where a quick-check exists in rsync. `--existing`/`--ignore-existing`/`-u` are receiver write-time policies (skipping the write / newer-destination guard) applied across the regular-file, `--delay-updates`-staged, hardlink-sibling, and special/device paths; `-u` implies `-M` metadata and uses a second-then-nanosecond strict `>` newer check; both correctly influence `--remove-source-files` (a skipped source is not removed). `-W/--whole-file` disables block-level delta (opt-in via `--delta`), folded into the wire `use_delta` so no protocol bump was needed, and makes `--fuzzy` inert; `--append`/`--append-verify` are rejected with `-W`. `--compress-threads=NUM` (1..64, client-only, never crosses the wire) sizes the zstd compression worker pool. No code was changed by this correction; the implementation had landed in earlier merge waves (feat/ignore-times, feat/ignore-existing via the newer `file_to_disk_secure_no_replace`/`linkat EEXIST` path, feat/size-only, feat/modify-window, feat/whole-file, feat/update, compression-threads).
 
@@ -915,7 +930,10 @@ These are the last compatibility items and the closing phase toward rsync flag p
 
 **Wire:** two trailing config-frame blocks after the `--iconv` spec, in fixed order — `send_privilege_options`/`receive_privilege_options` (one `super_mode` int, validated `0..2`), then `send_copy_as_options`/`receive_copy_as_options` (presence int + two int32 ids, validated `>= 0`, with `copy_as_set ⇒ use_metadata`). `PROTOCOL_VERSION` bumped **2.17.0 → 2.18.0**. **Divergences from rsync:** rsync's `--super` elevates the receiver and `--copy-as` actually switches its credentials; FastSync never elevates and only permits/forwards confined attempts, and `--copy-as` forces ownership rather than switching identity.
 
-**Honest status after the parity-completion wave (protocol 2.27.0), updated by the rsync-parity-stats, rsync-parity-options, rsync-parity-fs, parity-review, and no-wire parity-track-1 passes.** ✅ Parity 111 / ⚠️ Caveat 14 / ❌ Divergent 32 = 157 rows. Earlier revisions of this document reported "143 ✅ / 0 divergence / 0 partial"; that conflated "parsed and tested" with "rsync parity", because many rows carried documented behavioral differences and some short options were not parsed at all. This reclassification makes every difference explicit. The completion wave closed 23 previously-caveated rows (9 that triage showed were already parity, plus 14 genuine fixes) and turned the 17 inherently non-rsync rows — native daemon config/auth, the FastSync batch container, the safe-subset device/privilege flags, `-X`'s privileged namespaces, `--fake-super`'s native xattr format, and the `--old-args` no-op — into explicit ❌ divergences. The stats pass flipped `--delete-delay` to ✅ (actual-removal accounting), but the parity-review pass moved it back to ⚠️ because FastSync charged the `--max-delete` budget at plan/snapshot time and left a refilled snapshotted directory in place, whereas rsync charges on actual removals and recursively removes a queued directory (including content created after its plan). The no-wire parity-track-1 pass fixed both (actual-removal charging plus recursive deferred removal with an independent deferred-list cap), narrowing the caveat to the partial-delete ordering. The stats pass also reclassified `--out-format` to ❌ (protocol-specific `%b`/delta-`%c`), and sharpened the `--stats`/`--progress`/`--checksum-choice` residuals. The options pass flipped `--bwlimit` and `--ignore-errors` to ✅ (rsync-exact size parsing and ~100 ms leaky-bucket throttling, and rsync's skip-unreadable-subdir plus IO-error-suppressed deletion with exit 23) and emits rsync-format `--info=name/flist/del/remove/nonreg/progress` lines (real-run `deleting`/`*deleting` carried over a new trailing `report_deletes` wire bool, `PROTOCOL_VERSION` 2.26.0 → 2.27.0), while reclassifying `-M` over daemon/TCP and receiver-side `protect`/`risk` re-derivation to ❌ (no argv channel / receiver filter engine). The fs pass flipped `-d/--dirs` and `--iconv` to ✅ — recursive transfers now recreate empty source directories (and replace a blocking destination non-directory with an incoming directory); `-R --no-implied-dirs --files-from` places a listed file under a missing implied parent with default attributes instead of refusing; and `--iconv` now reproduces rsync's push direction (destination charset = the spec's REMOTE half) — and reclassified six rows to ❌ after reproducing their exact residual with differential tests: `--temp-dir` (the receiver confines the scratch dir to the receive root, so an absolute temp dir is deliberately rejected although standalone rsync follows it), the three basis-dir options (FastSync xxHash-verifies a basis hit while rsync's `--size-only` quick check installs the wrong basis content), `--delay-updates` (fixed staging name wipes an unrelated destination entry of that name), and `--dry-run` (would-delete report over-reports). `--fuzzy` was also reclassified to ❌ (deterministic heuristic with a 10× size window, not rsync's matcher), but its residual is the candidate-selection heuristic itself: the final tree is byte-exact by design, so no destination differential can expose it and the row is pinned by the `TestFuzzy` threshold suite rather than a byte-level rsync differential. The remaining ⚠️ rows are the ones with a documented residual (see the row notes and the **Parity Completion Wave (protocol 2.26.0)** section below).
+**Honest status after the parity 2.28.0 cycle (protocol 2.28.0), updated by the rsync-parity-stats, rsync-parity-options, rsync-parity-fs, parity-review, no-wire parity-track-1/2b and wire parity-track-4a/5a passes.** ✅ Parity 116 / ⚠️ Caveat 14 / ❌ Divergent 27 = 157 rows. Earlier revisions of this document reported "143 ✅ / 0 divergence / 0 partial"; that conflated "parsed and tested" with "rsync parity", because many rows carried documented behavioral differences and some short options were not parsed at all. This reclassification makes every difference explicit. The completion wave closed 23 previously-caveated rows (9 that triage showed were already parity, plus 14 genuine fixes) and turned the 17 inherently non-rsync rows — native daemon config/auth, the FastSync batch container, the safe-subset device/privilege flags, `-X`'s privileged namespaces, `--fake-super`'s native xattr format, and the `--old-args` no-op — into explicit ❌ divergences. The stats pass flipped `--delete-delay` to ✅ (actual-removal accounting), but the parity-review pass moved it back to ⚠️ because FastSync charged the `--max-delete` budget at plan/snapshot time and left a refilled snapshotted directory in place, whereas rsync charges on actual removals and recursively removes a queued directory (including content created after its plan). The no-wire parity-track-1 pass fixed both (actual-removal charging plus recursive deferred removal with an independent deferred-list cap), narrowing the caveat to the partial-delete ordering. The stats pass also reclassified `--out-format` to ❌ (protocol-specific `%b`/delta-`%c`), and sharpened the `--stats`/`--progress`/`--checksum-choice` residuals. The options pass flipped `--bwlimit` and `--ignore-errors` to ✅ (rsync-exact size parsing and ~100 ms leaky-bucket throttling, and rsync's skip-unreadable-subdir plus IO-error-suppressed deletion with exit 23) and emits rsync-format `--info=name/flist/del/remove/nonreg/progress` lines (real-run `deleting`/`*deleting` carried over a new trailing `report_deletes` wire bool, `PROTOCOL_VERSION` 2.26.0 → 2.27.0), while reclassifying `-M` over daemon/TCP
+and receiver-side `protect`/`risk` re-derivation to ❌ (no argv channel /
+receiver filter engine); the wire parity-track-4a pass later added that
+receiver filter engine, flipping `--filter=RULE` back to ✅ (see above). The fs pass flips `-d/--dirs` and `--iconv` to ✅ — recursive transfers now recreate empty source directories (and replace a blocking destination non-directory with an incoming directory); `-R --no-implied-dirs --files-from` places a listed file under a missing implied parent with default attributes instead of refusing; and `--iconv` now reproduces rsync's push direction (destination charset = the spec's REMOTE half) — and reclassified six rows to ❌ after reproducing their exact residual with differential tests: `--temp-dir` (the receiver confines the scratch dir to the receive root, so an absolute temp dir is deliberately rejected although standalone rsync follows it), the three basis-dir options (FastSync xxHash-verifies a basis hit while rsync's `--size-only` quick check installs the wrong basis content), `--delay-updates` (fixed staging name wipes an unrelated destination entry of that name), and `--dry-run` (would-delete report over-reports). `--fuzzy` was also reclassified to ❌ (deterministic heuristic with a 10× size window, not rsync's matcher), but its residual is the candidate-selection heuristic itself: the final tree is byte-exact by design, so no destination differential can expose it and the row is pinned by the `TestFuzzy` threshold suite rather than a byte-level rsync differential. (Track 5b later showed the name heuristic is in fact rsync's own and moved the row ❌ → ⚠️, leaving only the narrower delta size window as the residual; see the track 5b paragraph above.) The remaining ⚠️ rows are the ones with a documented residual (see the row notes and the **Parity Completion Wave (protocol 2.26.0)** section below).
 
 **Preserve-attribute split (protocol 2.21.0 → 2.22.0) — ✅ implemented.** FastSync splits the former single metadata bundle into four independent, rsync-compatible per-attribute flags — `-p/--perms`, `-t/--times`, `-o/--owner`, `-g/--group` — each with a negation (`--no-perms`/`--no-times`/`--no-owner`/`--no-group`, short `--no-p`/`--no-t`/`--no-o`/`--no-g`), plus `--no-preserve` clearing all four. `-a/--archive` is now full rsync `-rlptgoD` (owner and group included, though their application stays privilege-gated), `-A/--acls` implies `-p`, `-X/--xattrs` does not, `-E/--executability` sets only executability, and `-U`/`-N` do not imply `-t`. `--incremental`/`--delta` still auto-preserve perms+times unless the user explicitly negated them. Wire: the binary config frame gains four appended booleans (`preserve_perms`/`preserve_times`/`preserve_owner`/`preserve_group`) after `omit_link_times`, so `PROTOCOL_VERSION` is bumped **2.21.0 → 2.22.0**; the fixed-width `FileMetadata` layout is unchanged and the receiver gates the metadata frame on a derived `use_metadata`. Receiver behavior: each attribute is applied independently, directory modes are applied under `-p` (at the end of the transfer, alongside dir times), symlink mode under `-p`, and `-O/--omit-dir-times` suppresses directory times only. Documented divergences as of 2.22.0, **all but (d)/(e) removed by the rsync-parity wave (protocol 2.23.0)**: (a) the mode-masking divergence is **gone** — under `-p` the source mode is now copied exactly, including `S_IWGRP`/`S_IWOTH` and setuid/setgid/sticky; (b) a brand-new file without `-p` still gets `source_mode & ~umask` when metadata is present (else the historical fixed `0644`), and a new *directory* without `-p` still uses FastSync's `0755` default; (c) the `--chmod`-implies-`-p` divergence is **gone** — `--chmod` no longer implies `-p` (rsync parity); (d) `-o`/`-g` map by name on the receiver with a raw-numeric fallback (only numeric ids cross the wire); (e) a daemon module without `client owner = yes` does not refuse a plain `-a`/`-o`/`-g` — it forces super off, applies no ownership, and logs a warning, while explicit `--chown`/`--usermap`/`--groupmap`/`--numeric-ids`/`--copy-as`/`--super` are still refused.
 
@@ -1154,22 +1172,31 @@ These remain after the wave; the individual rows carry the precise wording.
   byte-identical), but a multi-directory `to-chk` denominator and per-directory
   name lines still differ; **`--out-format`** `%C` matches for every algorithm,
   but `%b`/`%c` count FastSync wire bytes (protocol-specific, hence ❌).
-- **`-n --delete`** ordering can differ from rsync's delete-during walk and a
-  filtered dry-run can over-report.
-- **Delete timing:** the default `--delete` remains delete-after rather than
-  rsync's delete-during; per-directory plans have generator-order/abort-boundary
-  differences; `--delete-before` keeps its pre-scan snapshot race; and
-  destination-only files matching an exclude are still removed (protection is
-  sender-derived). `--ignore-errors` exits 23 but its EACCES differential is not
+- **`-n --delete`** ordering can differ from rsync's delete-during walk (the
+  differential compares the sorted would-delete set).
+- **Delete timing:** plain `--delete` now defaults to rsync's delete-during
+  (lockstep track 6); the residual is the mid-transfer abort boundary, where
+  rsync's generator removes all extras ahead of its throttled sender while
+  FastSync removes only the reached directories (completed runs agree).
+  `--delete-before` keeps its pre-scan snapshot race; and while
+  base-rule `protect`/`risk` rules are now re-applied on the receiver (track 4a),
+  per-directory merge (`.rsync-filter`) protection is still sender-derived, so a
+  destination-only entry matching only a per-directory rule is not re-derived.
+  `--ignore-errors` exits 23 but its EACCES differential is not
   exercised in CI.
 - **`--delay-updates`** uses a fixed staging name with an advisory lock and
   deletes before publication; **`--temp-dir`** rejects absolute/foreign paths
   (deliberately confined, see the row); **`--remote-option`** is SSH-only.
   **`--iconv`** now matches rsync's push direction (destination charset = the
   spec's REMOTE half; a server `--iconv` overrides it).
-- **Basis dirs** do not re-apply attributes on a match, keep the
-  `--size-only` mtime caveat, and share the 256 MiB whole-file cap; **`--fuzzy`**
-  has a different tie-break order; and **`--bwlimit`** rejects rsync's
+- **Basis dirs** now use rsync's metadata quick-check by default (track 5a) and
+  stream a hit of any size; the FastSync-only `--verify-basis` restores the
+  stricter content equality. Remaining residuals: the relative-DIR resolution
+  base and the over-limit basis-MISS refusal. **`--fuzzy`** uses rsync's
+  name heuristic, but its candidate eligibility is bounded by the delta
+  engine (both files ≥ 16 KiB, size ratio ≤ 10×), a narrower window than
+  rsync's, so the selected basis — and the `--stats` bandwidth counters —
+  can differ while the tree stays byte-exact; and **`--bwlimit`** rejects rsync's
   `0`/decimal/suffixed rates.
 - **`--inc-recursive`/`--no-inc-recursive`** are not implemented (rejected).
 
@@ -1244,5 +1271,7 @@ Ranked by user demand, implementation complexity, and interoperability impact (_
 | `--tls` | TLS encryption (mutual auth) |
 | `--fastsync-server-path` | Path to fastsync-server binary |
 | `--server-host` / `--server-port` | Direct TCP connection |
+| `--verify-basis` | FastSync-only (long form, not in rsync): require a `--compare-dest`/`--copy-dest`/`--link-dest` basis hit to match the source by whole-file digest instead of trusting rsync's size+mtime (or `--size-only`) quick-check. Off by default (the default matches rsync). Crosses the wire (protocol 2.28.0) |
+| `--delete-commit` | FastSync-only (long form, not in rsync): restore the late whole-tree delete commit — the keep-set manifest is committed only after the entire transfer succeeded. Identical timing to `--delete-after`, and implemented as the same `delete_after` wire bool (no new field); it exists because plain `--delete` now defaults to `--delete-during` (lockstep track 6). Implies `--delete` and conflicts with any different timing flag |
 | Incremental sync | Skip unchanged files (size+mtime) |
 | Delta transfer | Block-level delta for changed files |

src/client/client_cli.c

@@ -997,6 +997,12 @@ static const OptionEntry OPTION_TABLE[] = {
     {"--delete-during", "--del", OPT_FLAG, offsetof(Config, delete_during)},
     {"--delete-delay", NULL, OPT_FLAG, offsetof(Config, delete_delay)},
     {"--delete-after", NULL, OPT_FLAG, offsetof(Config, delete_after)},
+    /* FastSync-only long spelling of the late whole-tree commit, which selects
+       the same timing as rsync's --delete-after in FastSync (the whole-tree
+       keep-set manifest is committed only after the entire transfer succeeded).
+       Plain --delete now defaults to delete-during, so this restores the old
+       FastSync behavior; it maps onto the same delete_after wire field. */
+    {"--delete-commit", NULL, OPT_FLAG, offsetof(Config, delete_after)},
     {"--delete-excluded", NULL, OPT_FLAG, offsetof(Config, delete_excluded)},
     {"--max-delete", NULL, OPT_SIGNED_INT, offsetof(Config, max_delete)},
     {"--ignore-errors", NULL, OPT_FLAG, offsetof(Config, ignore_errors)},
@@ -1054,6 +1060,11 @@ static const OptionEntry OPTION_TABLE[] = {
      * --remote-option is parsed.  --trust-sender is a local receiver policy and
      * never travels to the remote peer. */
     {"--trust-sender", NULL, OPT_FLAG, offsetof(Config, trust_sender)},
+    /* FastSync-only (not an rsync option): require a basis-hit's content to
+     * match the source by whole-file digest instead of trusting rsync's
+     * size+mtime quick-check.  Long-only; crosses the wire so the receiver
+     * performs the extra read/hash. */
+    {"--verify-basis", NULL, OPT_FLAG, offsetof(Config, verify_basis)},
 };
 
 /* Only boolean options with no required argument are safe to negate. */
@@ -1096,6 +1107,7 @@ static const NegatableOption NEGATABLE_OPTIONS[] = {
     {"xattrs", "X", offsetof(Config, preserve_xattrs)},
     {"acls", "A", offsetof(Config, preserve_acls)},
     {"fake-super", NULL, offsetof(Config, fake_super)},
+    {"verify-basis", NULL, offsetof(Config, verify_basis)},
 };
 
 static bool opt_is(const char* arg, const char* name, const char* alias) {
@@ -1507,7 +1519,9 @@ static bool cli_handle_table_option(CliParseCtx* ctx) {
   if (entry->offset == offsetof(Config, per_dir_filter) && config->per_dir_filter_count < INT_MAX)
     config->per_dir_filter_count++;
   /* A delete-timing flag selects when --delete removes extras, so it
-     implies --delete exactly like the rsync options do. */
+     implies --delete exactly like the rsync options do.  --delete-commit (the
+     FastSync-only late-commit spelling) is mapped onto delete_after and so is
+     covered here too. */
   if (entry->offset == offsetof(Config, delete_before) ||
       entry->offset == offsetof(Config, delete_during) ||
       entry->offset == offsetof(Config, delete_delay) ||
@@ -2561,6 +2575,18 @@ static bool cli_handle_outbuf_option(CliParseCtx* ctx) {
  * -1 on error. */
 static int cli_finalize_config(Config* config, bool verbose, bool no_delta, bool no_incremental) {
   set_log_level(config->quiet ? LOG_LEVEL_ERROR : (verbose ? LOG_LEVEL_DEBUG : LOG_LEVEL_WARNING));
+  /* rsync's plain --delete defaults to delete-during (--del): each directory's
+     extras are removed as that directory is processed, so space is freed
+     progressively and a tight destination never has to hold the whole old+new
+     tree at once.  The late whole-tree commit FastSync historically used is
+     still selected explicitly by --delete-after or by the FastSync-only long
+     spelling --delete-commit (an exact alias for --delete-after).  Resolve the
+     default on the client, before validation and before the config crosses the
+     wire, so exactly one timing flag is ever set; an explicit timing (including
+     --delete-commit) always wins. */
+  if (config->use_delete && !config->delete_before && !config->delete_during &&
+      !config->delete_delay && !config->delete_after)
+    config->delete_during = true;
   if (config->compress_choice) {
     int algo = compression_algo_from_name(config->compress_choice);
     if (algo >= 0) {

src/client/client_send.c

@@ -1047,53 +1047,6 @@ static bool files_from_list_check(const Config* config, ArrayList* missing_dest,
   return true;
 }
 
-/* Basis directories are honored by the receiver's per-file incremental check,
-   which (like every whole-file payload path in FastSync) is bounded by
-   MAX_RECEIVE_WHOLE_FILE_SIZE.  rsync would apply basis dirs to files of any
-   size; FastSync cannot, so when basis dirs are requested this preflight scan
-   refuses the run up front with a clear diagnostic instead of letting the
-   receiver abort the whole transfer mid-stream with no client explanation.
-   Returns true when the tree can be transferred. */
-static bool basis_oversize_preflight(const Config* config) {
-  PreparedScanner prepared;
-  if (!prepare_scanner(config, 0, &prepared))
-    return false;
-  DirectoryScanner* scanner =
-      directory_scanner_create_with_options(config->send_directory, &prepared.options);
-  if (!scanner) {
-    prepared_scanner_destroy(&prepared);
-    return false;
-  }
-  bool ok = true;
-  Chunk* chunk;
-  while ((chunk = directory_scanner_next(scanner)) != NULL) {
-    for (int i = 0; i < chunk->element_count; i++) {
-      File* f = chunk->items[i];
-      if (f == NULL || f->is_dir || f->data == NULL || f->data->size <= MAX_RECEIVE_WHOLE_FILE_SIZE)
-        continue;
-      char* escaped = output_escape(file_wire_path(f), config->eight_bit_output);
-      log_message(LOG_LEVEL_ERROR,
-                  "%s is %llu bytes, larger than the %llu-byte whole-file transfer limit; "
-                  "--compare-dest/--copy-dest/--link-dest cannot sync files above this limit",
-                  escaped ? escaped : "<allocation failed>", (unsigned long long)f->data->size,
-                  (unsigned long long)MAX_RECEIVE_WHOLE_FILE_SIZE);
-      free(escaped);
-      ok = false;
-      break;
-    }
-    chunk_destroy(chunk);
-    if (!ok)
-      break;
-  }
-  if (directory_scanner_failed(scanner) || directory_scanner_had_io_error(scanner))
-    ok = false;
-  /* The scanner borrows prepared.options' base_filters/hardlinks pointers, so
-     prepared must outlive the scanner. */
-  directory_scanner_destroy(scanner);
-  prepared_scanner_destroy(&prepared);
-  return ok;
-}
-
 /* Read the daemon's MOTD frame and, unless --no-motd, display it on stdout.
  *
  * The daemon sends the MOTD as the first thing after the config-frame STATUS_OK
@@ -1939,11 +1892,13 @@ static int incremental_check(Client* client, File* file, const Config* config,
     return -1;
   if (!send_n_data(client->file_descriptor, &mtime_nsec, sizeof(mtime_nsec)))
     return -1;
-  /* With alternate basis directories the receiver must be able to verify the
-   * content of every candidate basis file, so the sender supplies its whole-file
-   * digest (computed with the negotiated --checksum-choice algorithm and
-   * --checksum-seed) for every file even when --checksum was not requested. */
-  if (config->checksum || config_has_basis(config)) {
+  /* The whole-file digest (negotiated --checksum-choice algorithm and
+   * --checksum-seed) is only needed when it drives a decision: --checksum's
+   * per-file quick check, or a --verify-basis content equality.  Under the
+   * default metadata quick-check the receiver never reads it, so the sender
+   * skips the full-file read/hash exactly as rsync does for a plain
+   * --link-dest run. */
+  if (config->checksum || config->verify_basis) {
     uint8_t digest[CHECKSUM_MAX_DIGEST_LEN];
     size_t digest_len = 0;
     if (!file_checksum(file, (ChecksumAlgo)config->checksum_algo, config->checksum_seed, digest,
@@ -1954,6 +1909,15 @@ static int incremental_check(Client* client, File* file, const Config* config,
         !send_n_data(client->file_descriptor, digest, wire_len))
       return -1;
   }
+  /* Basis directories: the receiver materializes a hit from the basis without a
+   * data frame, so it would otherwise only have the basis inode's metadata.
+   * Transmit the SOURCE metadata with the check (rsync's copy-then-fix) so a
+   * --copy-dest hit / --link-dest copy fallback applies the source's
+   * attributes.  Symmetric with incremental_check_receive_request. */
+  if (config_has_basis(config) && config->use_metadata) {
+    if (!metadata_send(client->file_descriptor, file->metadata))
+      return -1;
+  }
   Status s;
   if (!receive_status(client->file_descriptor, &s))
     return -1;
@@ -2193,12 +2157,6 @@ static int send_dry_run_remote(Config* config) {
   }
   if (missing_args)
     array_list_delete(missing_args);
-  /* Alternate basis dirs force the whole-file per-file check on the real
-     receiver; refuse an oversize source up front exactly as send_files does so
-     dry-run reports the same clear diagnostic instead of aborting mid-stream. */
-  if (config_has_basis(config) && !basis_oversize_preflight(config))
-    return 1;
-
   /* A live session may follow, so arm graceful abort handling. */
   client_set_abort_armed(true);
   Client* client = connect_transfer_client(config);
@@ -3240,11 +3198,6 @@ int send_files(Config* config) {
       array_list_delete(missing_args);
     return 1;
   }
-  if (config_has_basis(config) && !basis_oversize_preflight(config)) {
-    if (missing_args)
-      array_list_delete(missing_args);
-    return 1;
-  }
 
   /* From here on a server session may be live, so Ctrl-C/SIGTERM should set the
      abort flag (and be forwarded as STATUS_ABORT) instead of terminating. */
@@ -3334,7 +3287,8 @@ int send_files(Config* config) {
       prepared.options.synced_dirs = synced_dirs;
     }
   }
-  /* The late-timing modes (plain --delete / --delete-after) build the manifest
+  /* The late-timing modes (--delete-after/--delete-commit and a plain --delete
+     that fell back from per-dir mode because of -d/--dirs) build the manifest
      while streaming and send it after the last data frame.  --delete-before
      sends a whole-tree keep-set up front; --delete-during/--delete-delay build a
      per-directory plan set up front (paths only) and stream the plans alongside
@@ -3682,11 +3636,6 @@ int send_files_multithreaded(Config** config_ptr) {
       array_list_delete(missing_args);
     return 1;
   }
-  if (config_has_basis(config) && !basis_oversize_preflight(config)) {
-    if (missing_args)
-      array_list_delete(missing_args);
-    return 1;
-  }
 
   /* Armed only once a session may go live (see send_files). */
   client_set_abort_armed(true);

src/client/usage.c

@@ -62,8 +62,7 @@ void print_usage(void) {
   printf("  NOTE: the FastSync batch format is NOT interoperable with rsync's batch\n");
   printf("  files (different container format); do not mix the two tools.\n");
   printf("  --delete            Delete files on receiver not in source\n");
-  printf("                      (default timing: delete only after the whole\n");
-  printf("                      transfer has succeeded)\n");
+  printf("                      (default timing: delete-during, like rsync --del)\n");
   printf("  --delete-before     Delete extras before the transfer starts\n");
   printf("                      (implies --delete)\n");
   printf("  --delete-during     Delete a directory's extras as that directory is\n");
@@ -72,7 +71,9 @@ void print_usage(void) {
   printf("  --delete-delay      Record the extras during the scan but remove them\n");
   printf("                      only after a successful transfer (implies --delete)\n");
   printf("  --delete-after      Delete only after the whole transfer succeeded\n");
-  printf("                      (the default --delete timing; implies --delete)\n");
+  printf("                      (implies --delete)\n");
+  printf("  --delete-commit     FastSync-only: restore the late whole-tree commit\n");
+  printf("                      (identical to --delete-after; implies --delete)\n");
   printf("  --delete-excluded   Also delete destination files that were excluded on\n");
   printf("                      the source (default protects them, matching rsync)\n");
   printf("  --max-delete=NUM    Delete at most NUM destination entries per run; if the\n");
@@ -93,7 +94,8 @@ void print_usage(void) {
   printf("  -m, --prune-empty-dirs  Do not create empty directories (a recursive transfer\n");
   printf("                      otherwise recreates them, like rsync)\n");
   printf("  Note: each timing flag implies --delete.  Combining a timing flag with\n");
-  printf("  --no-delete (in either order) is rejected as a config error.\n");
+  printf("  --no-delete (in either order) is rejected as a config error, as is more\n");
+  printf("  than one timing flag.\n");
   printf("  --ignore-existing  Skip files that already exist on receiver\n");
   printf("  --delay-updates    Put updated files into place only at the end of transfer\n");
   printf("  --dirs, -d, --old-dirs, --old-d  Transfer the named directory entries without\n");
@@ -138,6 +140,9 @@ void print_usage(void) {
   printf("                    into the destination instead of transferring its data\n");
   printf("  --link-dest <dir>   Like --copy-dest, but hard-links the unchanged file from DIR\n");
   printf("                    into the destination (repeatable; earlier DIRs win)\n");
+  printf("  --verify-basis      FastSync-only: require a basis hit's content to match the\n");
+  printf("                    source by whole-file digest instead of trusting rsync's\n");
+  printf("                    size+mtime (or --size-only) quick-check\n");
   printf("  --checksum-choice, --cc <alg>  Whole-file checksum algorithm for --incremental/\n");
   printf("                    --checksum compares.  Accepted: xxh128 (default), xxh3, xxh64\n");
   printf("                    (aka xxhash), md5, md4, sha1, or none.  A two-name\n");

src/server/receiver.c

@@ -305,14 +305,16 @@ int receiver_process(Config* config, int file_descriptor, const ReceiverSink* si
 
 /* Runs the whole receive loop.  The delete manifest may legitimately arrive
    either FIRST (--delete-before / --delete-during: the sender transmits the
-   validated keep-set before any file data) or LAST (plain --delete /
-   --delete-after / --delete-delay: the manifest closes the data stream).  In
+   validated keep-set before any file data) or LAST (--delete-after /
+   --delete-commit / --delete-delay: the manifest closes the data stream).  In
    the early modes the receiver deletes as soon as the manifest has been read
    and acknowledges with STATUS_OK so the sender only starts streaming once the
    deletion has committed (or failed); in the late modes the manifest is held
    and the deletion is committed only after the terminal STATUS_FINISHED proves
-   the whole transfer succeeded.  See receiver_process_pending() for how the -m
-   receiver defers that commit until its disk writer has drained. */
+   the whole transfer succeeded.  A plain --delete defaults to the per-directory
+   delete-during plan mode (no manifest at all).  See
+   receiver_process_pending() for how the -m receiver defers that commit until
+   its disk writer has drained. */
 int receiver_process_pending(Config* config, int file_descriptor, const ReceiverSink* sink,
                              DeleteManifest** pending_manifest, DeletePlanSession** pending_plans) {
   Status status;

src/shared/checksum.c

@@ -224,23 +224,31 @@ bool checksum_digest_file(ChecksumAlgo algo, uint64_t seed, const char* path, ui
   if (fd < 0)
     return false;
 
+  bool ok = checksum_digest_fd(algo, seed, fd, out, out_capacity, out_len);
+  close(fd);
+  return ok;
+}
+
+bool checksum_digest_fd(ChecksumAlgo algo, uint64_t seed, int fd, uint8_t* out, size_t out_capacity,
+                        size_t* out_len) {
+  if (fd < 0 || !out || !out_len || out_capacity < CHECKSUM_MAX_DIGEST_LEN)
+    return false;
+
   if (algo == CHECKSUM_ALGO_NONE) {
     /* No checksum requested: nothing to read; an empty digest succeeds. */
-    close(fd);
     *out_len = 0;
     return true;
   }
 
   uint8_t buffer[64 * 1024];
   bool ok = false;
+  lseek(fd, 0, SEEK_SET);
 
   if (algo == CHECKSUM_ALGO_MD5 || algo == CHECKSUM_ALGO_SHA1) {
     const EVP_MD* md = algo == CHECKSUM_ALGO_MD5 ? EVP_md5() : EVP_sha1();
     EVP_MD_CTX* ctx = EVP_MD_CTX_new();
-    if (!ctx) {
-      close(fd);
+    if (!ctx)
       return false;
-    }
     unsigned int digest_len = 0;
     if (EVP_DigestInit_ex(ctx, md, NULL) == 1) {
       ok = true;
@@ -259,7 +267,6 @@ bool checksum_digest_file(ChecksumAlgo algo, uint64_t seed, const char* path, ui
         ok = false;
     }
     EVP_MD_CTX_free(ctx);
-    close(fd);
     return ok;
   }
 
@@ -276,7 +283,6 @@ bool checksum_digest_file(ChecksumAlgo algo, uint64_t seed, const char* path, ui
       md4_final(&ctx, out);
       *out_len = 16;
     }
-    close(fd);
     return ok;
   }
 
@@ -286,16 +292,13 @@ bool checksum_digest_file(ChecksumAlgo algo, uint64_t seed, const char* path, ui
     XXH64_reset(&xxh64, seed);
   } else if (algo == CHECKSUM_ALGO_XXH3 || algo == CHECKSUM_ALGO_XXH128) {
     xxh3 = XXH3_createState();
-    if (!xxh3) {
-      close(fd);
+    if (!xxh3)
       return false;
-    }
     if (algo == CHECKSUM_ALGO_XXH3)
       XXH3_64bits_reset_withSeed(xxh3, seed);
     else
       XXH3_128bits_reset_withSeed(xxh3, seed);
   } else {
-    close(fd);
     return false;
   }
 
@@ -329,7 +332,6 @@ bool checksum_digest_file(ChecksumAlgo algo, uint64_t seed, const char* path, ui
   }
   if (xxh3)
     XXH3_freeState(xxh3);
-  close(fd);
   return ok;
 }
 

src/shared/checksum.h

@@ -51,6 +51,13 @@ bool checksum_digest(ChecksumAlgo algo, uint64_t seed, const void* data, size_t
 bool checksum_digest_file(ChecksumAlgo algo, uint64_t seed, const char* path, uint8_t* out,
                           size_t out_capacity, size_t* out_len);
 
+/* Descriptor form of the streaming digest: rewinds `fd` to the start and hashes
+ * to EOF without closing it.  Used by the --verify-basis path to hash an
+ * already-open, root-confined basis descriptor.  Same contract as
+ * checksum_digest_file. */
+bool checksum_digest_fd(ChecksumAlgo algo, uint64_t seed, int fd, uint8_t* out, size_t out_capacity,
+                        size_t* out_len);
+
 /* Resolve a --checksum-choice string (case-insensitive) to an algorithm id.
  * Accepts "xxh64"/"xxhash", "xxh3", "xxh128", "md5", "md4", "sha1", "none".
  * "auto" is not an algorithm here; the caller resolves it to the negotiated

src/shared/config.c

@@ -791,6 +791,8 @@ void config_delete(Config* config) {
   if (config->filters) {
     array_list_delete(config->filters);
   }
+  filter_rule_list_free(config->protect_rules);
+  config->protect_rules = NULL;
   /* A --delay-updates staging tree is transient receiver state: remove any
      leftovers on every exit path (success already emptied it). */
   if (config->delay_context)
@@ -1026,6 +1028,124 @@ static bool receive_basis_entries(int fd, Config* c, ConfigStringBudget* budget)
   return true;
 }
 
+/* Receiver-side delete-protection rules (protocol 2.28.0).  The sender compiles
+ * its command-line selection rules exactly as the scanner does and streams the
+ * result as one bounded, self-describing block (count + per-rule records); the
+ * receiver reconstructs a FilterRuleList for the --delete extras walk.  owner
+ * and pattern are charged through the shared ConfigStringBudget and the block
+ * additionally enforces MAX_FILTER_RULES / MAX_FILTER_BYTES. */
+static bool send_protect_entries(int fd, const Config* c) {
+  int count = c->filters ? c->filters->size : 0;
+  const char** texts = NULL;
+  if (count > 0) {
+    texts = malloc((size_t)count * sizeof(char*));
+    if (!texts)
+      return false;
+    for (int i = 0; i < count; i++)
+      texts[i] = (const char*)c->filters->items[i];
+  }
+  char err[160];
+  FilterRuleList* rules =
+      filter_base_build(texts, count, c->cvs_exclude, c->delete_excluded, err, sizeof(err));
+  free(texts);
+  if (!rules) {
+    log_message(LOG_LEVEL_ERROR, "invalid filter rule: %s", err);
+    return false;
+  }
+  bool ok = send_int(fd, rules->count);
+  for (int i = 0; ok && i < rules->count; i++) {
+    const FilterRule* r = rules->items[i];
+    /* Mirror the receiver's limit so the peer never receives a rule it will
+       reject as a protocol error. */
+    if (r->pattern && strlen(r->pattern) > MAX_PROTECT_PATTERN_LEN) {
+      log_message(LOG_LEVEL_ERROR, "filter pattern exceeds %d bytes", MAX_PROTECT_PATTERN_LEN);
+      filter_rule_list_free(rules);
+      return false;
+    }
+    ok = send_int(fd, (int)r->action) && send_int(fd, (int)r->sides) &&
+         send_int(fd, r->anchored ? 1 : 0) && send_int(fd, r->dir_only ? 1 : 0) &&
+         send_int(fd, r->negate ? 1 : 0) && send_str(fd, r->owner ? r->owner : "") &&
+         send_str(fd, r->pattern ? r->pattern : "");
+  }
+  filter_rule_list_free(rules);
+  return ok;
+}
+
+static bool receive_protect_entries(int fd, Config* c, ConfigStringBudget* budget) {
+  int count;
+  if (!receive_int(fd, &count))
+    return false;
+  if (count < 0 || count > MAX_FILTER_RULES)
+    return false;
+  if (count == 0)
+    return true;
+  FilterRuleList* list = filter_rule_list_create();
+  if (!list)
+    return false;
+  size_t pattern_bytes = 0;
+  for (int i = 0; i < count; i++) {
+    int action;
+    int sides;
+    bool anchored;
+    bool dir_only;
+    bool negate;
+    if (!receive_int(fd, &action) ||
+        (action != FILTER_ACTION_EXCLUDE && action != FILTER_ACTION_INCLUDE) ||
+        !receive_int(fd, &sides) || sides < (int)FILTER_SIDE_SENDER ||
+        sides > (int)(FILTER_SIDE_SENDER | FILTER_SIDE_RECEIVER) ||
+        !receive_wire_bool(fd, &anchored) || !receive_wire_bool(fd, &dir_only) ||
+        !receive_wire_bool(fd, &negate))
+      goto fail;
+    char* owner = config_receive_str(fd, budget);
+    if (!owner)
+      goto fail;
+    char* pattern = config_receive_str(fd, budget);
+    if (!pattern || pattern[0] == '\0') {
+      free(owner);
+      free(pattern);
+      goto fail;
+    }
+    /* A pattern too long to be evaluated by glob_match against a PATH_MAX path
+       would silently fail to match and leave a protect rule inert (fail-open:
+       the entry is then deleted).  Reject it up front as a protocol error
+       rather than accept a rule that can never shield anything. */
+    if (strlen(pattern) > MAX_PROTECT_PATTERN_LEN) {
+      free(owner);
+      free(pattern);
+      goto fail;
+    }
+    size_t bytes = strlen(owner) + strlen(pattern);
+    if (bytes > MAX_FILTER_BYTES - pattern_bytes) {
+      free(owner);
+      free(pattern);
+      goto fail;
+    }
+    pattern_bytes += bytes;
+    FilterRule* rule = calloc(1, sizeof(FilterRule));
+    if (!rule) {
+      free(owner);
+      free(pattern);
+      goto fail;
+    }
+    rule->action = (FilterAction)action;
+    rule->sides = (unsigned)sides;
+    rule->anchored = anchored;
+    rule->dir_only = dir_only;
+    rule->negate = negate;
+    rule->owner = owner;
+    rule->pattern = pattern;
+    if (!filter_rule_list_add(list, rule)) {
+      filter_rule_free(rule);
+      goto fail;
+    }
+  }
+  c->protect_rules = list;
+  return true;
+fail:
+  filter_rule_list_free(list);
+  return false;
+}
+
 static bool send_identity_entries(int fd, const IdentityMap* map, int count) {
   for (int i = 0; i < count; i++) {
     if (!send_int(fd, map[i].from) || !send_int(fd, map[i].from_hi) || !send_int(fd, map[i].to) ||
@@ -1153,6 +1273,9 @@ fail:
 #define CONFIG_RECV_BLOCK_IDMAP(name)                                                              \
   receive_identity_entries(fd, budget, c->name##_count, &c->name)
 
+#define CONFIG_SEND_BLOCK_PROTECT_RULES(name) send_protect_entries(fd, c)
+#define CONFIG_RECV_BLOCK_PROTECT_RULES(name) receive_protect_entries(fd, c, budget)
+
 /* One table entry, applied in sequence.  XSEND/XRECV are statement macros so
  * consecutive entries read as a plain sequence of assignments. */
 #define XSEND(name, ctype, def, kind) ok = ok && (CONFIG_SEND_##kind(name));
@@ -1190,6 +1313,7 @@ CONFIG_DEFINE_SEND(send_privilege_options, CONFIG_WIRE_PRIVILEGE_FIELDS)
 CONFIG_DEFINE_SEND(send_copy_as_options, CONFIG_WIRE_COPY_AS_FIELDS)
 CONFIG_DEFINE_SEND(send_output_options, CONFIG_WIRE_OUTPUT_FIELDS)
 CONFIG_DEFINE_SEND(send_codec_options, CONFIG_WIRE_CODEC_FIELDS)
+CONFIG_DEFINE_SEND(send_protect_options, CONFIG_WIRE_PROTECT_FIELDS)
 
 CONFIG_DEFINE_RECV(receive_core_fields, CONFIG_WIRE_CORE_FIELDS)
 CONFIG_DEFINE_RECV(receive_delta_fields, CONFIG_WIRE_DELTA_FIELDS)
@@ -1210,6 +1334,7 @@ CONFIG_DEFINE_RECV(receive_privilege_options, CONFIG_WIRE_PRIVILEGE_FIELDS)
 CONFIG_DEFINE_RECV(receive_copy_as_options, CONFIG_WIRE_COPY_AS_FIELDS)
 CONFIG_DEFINE_RECV(receive_output_options, CONFIG_WIRE_OUTPUT_FIELDS)
 CONFIG_DEFINE_RECV(receive_codec_options, CONFIG_WIRE_CODEC_FIELDS)
+CONFIG_DEFINE_RECV(receive_protect_options, CONFIG_WIRE_PROTECT_FIELDS)
 
 #undef XSEND
 #undef XRECV
@@ -1328,7 +1453,8 @@ bool config_send_wire_block(int file_descriptor, const Config* config) {
          send_privilege_options(file_descriptor, config) &&
          send_copy_as_options(file_descriptor, config) &&
          send_output_options(file_descriptor, config) &&
-         send_codec_options(file_descriptor, config);
+         send_codec_options(file_descriptor, config) &&
+         send_protect_options(file_descriptor, config);
 }
 
 bool config_send(int file_descriptor, const Config* config) {
@@ -1400,7 +1526,8 @@ Config* config_receive_with_validate(int file_descriptor, ConfigValidateFunc val
       !receive_privilege_options(file_descriptor, config, &budget) ||
       !receive_copy_as_options(file_descriptor, config, &budget) ||
       !receive_output_options(file_descriptor, config, &budget) ||
-      !receive_codec_options(file_descriptor, config, &budget))
+      !receive_codec_options(file_descriptor, config, &budget) ||
+      !receive_protect_options(file_descriptor, config, &budget))
     goto error;
   /* Validate/normalize the negotiated codec.  compress_choice is the human
    * spelling (NULL or "" when -z was not given); compression_algo is the

src/shared/config.h

@@ -4,6 +4,7 @@
 #include "array_list.h"
 #include "checksum.h"
 #include "compression.h"
+#include "filter.h"
 #include <stdbool.h>
 #include <stdint.h>
 #include <stdio.h>
@@ -197,9 +198,18 @@ typedef enum SuperMode { SUPER_MODE_AUTO = 0, SUPER_MODE_ON = 1, SUPER_MODE_OFF
   X(skip_compress_count, int, 0, INT_SKIPCOUNT)                                                    \
   X(skip_compress_suffixes, char**, NULL, BLOCK_SKIP_SUFFIXES)
 
+/* FastSync-only --verify-basis (protocol 2.28.0, no version bump by project
+ * decision): restores the stricter content equality on a basis hit.  By
+ * default a basis hit is accepted on rsync's metadata quick-check alone (equal
+ * size plus equal mtime, or size alone under --size-only); with this flag the
+ * receiver ALSO requires the basis bytes' whole-file digest (the negotiated
+ * --checksum-choice algorithm) to equal the sender's, exactly FastSync's
+ * historical behavior.  It is a receiver policy and crosses the wire so the
+ * receiver knows whether to read and hash the basis content. */
 #define CONFIG_WIRE_BASIS_FIELDS(X)                                                                \
   X(basis_count, int, 0, INT_BASISCOUNT)                                                           \
-  X(basis_dirs, BasisDest*, NULL, BLOCK_BASIS)
+  X(basis_dirs, BasisDest*, NULL, BLOCK_BASIS)                                                     \
+  X(verify_basis, bool, false, BOOL)
 
 #define CONFIG_WIRE_FUZZY_FIELDS(X) X(fuzzy, bool, false, BOOL)
 
@@ -293,6 +303,20 @@ typedef enum SuperMode { SUPER_MODE_AUTO = 0, SUPER_MODE_ON = 1, SUPER_MODE_OFF
 #define CONFIG_WIRE_CODEC_FIELDS(X)                                                                \
   X(compression_algo, int, COMPRESSION_ALGO_ZSTD, INT_COMPRESSION_ALGO)
 
+/* Receiver-side delete-protection filter rules (protocol 2.28.0).  The sender
+ * compiles its root-level selection rules exactly as the scanner does
+ * (filter_base_build over --filter/-f/--exclude/--include/-C) and streams them
+ * as one self-describing, bounded block (count followed by per-rule records).
+ * The receiver reconstructs `protect_rules` and evaluates them against
+ * DESTINATION-ONLY entries during the --delete extras walk, so a
+ * `protect`/`P` rule protects an extra that never appeared on the sender
+ * (rsync re-derives deletion protection from the filter list; FastSync
+ * historically derived it only from the source scan).  `protect_rules` is NULL
+ * on the sender and is owned/freed by the receiver Config.  Bounded by
+ * MAX_FILTER_RULES and MAX_FILTER_BYTES; an unknown action/sides is a protocol
+ * error. */
+#define CONFIG_WIRE_PROTECT_FIELDS(X) X(protect_rules, FilterRuleList*, NULL, BLOCK_PROTECT_RULES)
+
 /* All serialized fields, in exact wire order.  Concatenating the per-segment
  * lists here is what keeps the declaration order = the wire order. */
 #define CONFIG_WIRE_FIELDS(X)                                                                      \
@@ -315,7 +339,8 @@ typedef enum SuperMode { SUPER_MODE_AUTO = 0, SUPER_MODE_ON = 1, SUPER_MODE_OFF
   CONFIG_WIRE_PRIVILEGE_FIELDS(X)                                                                  \
   CONFIG_WIRE_COPY_AS_FIELDS(X)                                                                    \
   CONFIG_WIRE_OUTPUT_FIELDS(X)                                                                     \
-  CONFIG_WIRE_CODEC_FIELDS(X)
+  CONFIG_WIRE_CODEC_FIELDS(X)                                                                      \
+  CONFIG_WIRE_PROTECT_FIELDS(X)
 
 typedef struct Config {
   /* -j/--threads=N: number of parallel scanner worker threads for the -m
@@ -617,10 +642,14 @@ typedef struct Config {
      source directory is streamed in directory order, and the receiver removes
      each directory's extras when its plan arrives (during) or snapshots them
      and removes them only after a successful transfer (delay).  delete_after
-     (and plain --delete) keep the whole-tree commit mode: extras are removed
-     from a fresh end-of-transfer destination scan only after the whole transfer
-     succeeded.  See config_delete_timing_early()/config_delete_timing_per_dir()
-     below. */
+     keeps the whole-tree commit mode: extras are removed from a fresh
+     end-of-transfer destination scan only after the whole transfer succeeded.
+     A plain --delete with no explicit timing flag defaults to delete_during on
+     the client (cli_finalize_config), matching rsync's --del default; the old
+     late-commit behavior is selected explicitly by --delete-after or the
+     FastSync-only long spelling --delete-commit (an exact alias for
+     --delete-after, mapped onto the same wire field).  See
+     config_delete_timing_early()/config_delete_timing_per_dir() below. */
   /* partial_dir */
   // PR #174: Partial transfer resumption
   /* suffix */
@@ -1025,11 +1054,31 @@ typedef struct Config {
  * same-version handshake (config_receive rejects a mismatched version before
  * parsing anything else) keeps mixed deployments from ever reaching that
  * state. */
+/* (9) Receiver-side delete protection (still protocol 2.28.0): the config frame
+ * gains one trailing self-describing block carrying the sender's compiled base
+ * filter rules so the receiver can protect DESTINATION-ONLY entries from
+ * --delete with `protect`/`risk` rules (rsync parity).  The block appends after
+ * compression_algo; see CONFIG_WIRE_PROTECT_FIELDS. */
 #define PROTOCOL_VERSION "2.28.0"
 #define DEFAULT_CHUNK_SIZE (10 * 1024 * 1024)
 /* Upper bound on total basis-dir entries (rsync caps --link-dest at 20). */
 #define MAX_BASIS_DIRS 64
 
+/* Bounds on the received receiver-side delete-protection rule block.  The rule
+ * count and the aggregate pattern+owner bytes are each capped so a hostile
+ * peer cannot pin unbounded pre-auth memory; both are validated strictly on
+ * receive (alongside the per-string ConfigStringBudget). */
+/* A peer may supply protect rules; cap the list so a crafted config cannot make
+ * the receiver's delete walk evaluate an unbounded number of glob patterns per
+ * destination entry (glob_match is O(pattern x path)).  1024 is far above any
+ * legitimate selection. */
+#define MAX_FILTER_RULES 1024
+#define MAX_FILTER_BYTES (256 * 1024)
+/* glob_match's DP is capped at 64 Mi work units; a pattern longer than this
+ * could exceed the cap against a PATH_MAX path and silently stop matching,
+ * leaving a protect rule inert.  Reject such a rule at receive time. */
+#define MAX_PROTECT_PATTERN_LEN 8192
+
 /* Upper bound on the number of --skip-compress suffixes accepted from the wire.
  * Each suffix is an independent wire string (up to MAX_STRING_SIZE = 64 KiB), so
  * without this a hostile pre-auth client could otherwise retain
@@ -1131,8 +1180,11 @@ bool config_delete_timing_early(const Config* config);
  * commits them only after a fully-successful transfer (delay). */
 bool config_delete_timing_per_dir(const Config* config);
 /* Delete-timing sanity: with deletion enabled at most one timing flag may be
- * set (none = the default delete-after commit timing); without deletion no
- * timing flag may be set (each timing flag implies --delete). */
+ * set; without deletion no timing flag may be set (each timing flag implies
+ * --delete).  A plain --delete is normalized to delete_during by
+ * cli_finalize_config on the client, so a transmitted use_delete config always
+ * carries exactly one timing; the zero-timing case remains valid only for a
+ * config that has not been through the CLI. */
 bool config_has_valid_delete_timing(const Config* config);
 
 /* Single source of truth for the cross-field ("combination") invariants a

src/shared/delete_plan.c

@@ -331,6 +331,8 @@ static int send_plan_node(int fd, DeletePlanSender* sender, PlanNode* node) {
       return -1;
     sender->config_sent = true;
   }
+  if (!send_int(fd, 1)) /* apply = true */
+    return -1;
   if (!send_wire_str(fd, node->dir))
     return -1;
   if (send_str_section(fd, node->dirs) != 0 || send_str_section(fd, node->files) != 0)
@@ -339,6 +341,29 @@ static int send_plan_node(int fd, DeletePlanSender* sender, PlanNode* node) {
   return 0;
 }
 
+/* Transmit the one-shot per-run config block (protected prefixes, size-pruned
+ * mirrors, --delete-missing-args exact paths) on its own carrier frame, with
+ * apply=false so the receiver consumes the config but walks nothing.  This is
+ * how the config still reaches the receiver when the scope allows no directory
+ * plan at all (a --files-from list of bare files synchronizes no directory):
+ * without it, the missing-args exact deletions would be lost.  Idempotent. */
+static int send_config_only(int fd, DeletePlanSender* sender) {
+  if (!sender || sender->config_sent)
+    return 0;
+  if (!send_status(fd, STATUS_DELETE_PLAN) || !send_int(fd, 1))
+    return -1;
+  if (send_str_section(fd, sender->protected_prefixes) != 0 ||
+      send_str_section(fd, sender->size_skipped) != 0 ||
+      send_str_section(fd, sender->missing_args) != 0)
+    return -1;
+  sender->config_sent = true;
+  if (!send_int(fd, 0)) /* apply = false */
+    return -1;
+  if (!send_wire_str(fd, ".") || !send_int(fd, 0) || !send_int(fd, 0))
+    return -1;
+  return 0;
+}
+
 static int send_prefix_plan(int fd, DeletePlanSender* sender, const char* dir) {
   PlanNode* node = plan_find(sender, dir);
   if (!node || node->sent)
@@ -354,6 +379,10 @@ int delete_plan_send_root(int fd, DeletePlanSender* sender) {
   const char* root = sender->walk_root ? sender->walk_root : ".";
   if (!plan_ensure(sender, root))
     return -1;
+  /* Put the config block on the wire first, on its own carrier frame, so the
+     receiver always sees it even when the scope permits no directory plan. */
+  if (send_config_only(fd, sender) != 0)
+    return -1;
   return send_prefix_plan(fd, sender, root);
 }
 
@@ -546,12 +575,18 @@ static int open_plan_dir(const Config* config, const char* dir) {
 typedef struct PlanSkips {
   DeleteSkipEntry* entries;
   int count;
+  /* Receiver-side delete-protection rules received on the config frame (NULL
+     when the sender sent none).  Evaluated per extra so a protect/risk rule is
+     honored under --delete-during/--delete-delay exactly like the whole-tree
+     commit walker. */
+  const FilterRuleList* protect_rules;
 } PlanSkips;
 
 static bool build_plan_skips(const Config* config, const DeletePlanSession* session,
                              PlanSkips* out) {
   out->entries = NULL;
   out->count = 0;
+  out->protect_rules = config->protect_rules;
   int count = (config->delay_updates ? 1 : 0) + config->basis_count +
               session->protected_prefixes->size + session->size_skipped->size;
   if (count == 0)
@@ -733,6 +768,10 @@ static bool process_children(int dirfd, const char* dir_rel, const ArrayList* ke
     bool is_dir = S_ISDIR(st.st_mode);
     bool in_keep_dirs = is_dir && list_contains_str(keep_dirs, entry->d_name);
     bool in_keep_files = !is_dir && list_contains_str(keep_files, entry->d_name);
+    bool rule_protected =
+        skips->protect_rules &&
+        filter_rules_apply_side(skips->protect_rules, child_rel, entry->d_name, is_dir,
+                                FILTER_SIDE_RECEIVER) == FILTER_ACTION_PROTECT;
     if (in_keep_dirs) {
       local_survives = true;
     } else if (keep_dirs && !is_dir && list_contains_str(keep_dirs, entry->d_name)) {
@@ -750,11 +789,18 @@ static bool process_children(int dirfd, const char* dir_rel, const ArrayList* ke
       else if (!removed)
         local_survives = true;
     } else if (is_dir) {
-      bool removed = false;
-      if (!process_extra_dir(dirfd, entry->d_name, child_rel, force_now, skips, session, &removed))
-        operation_ok = false;
-      else if (!removed)
+      if (rule_protected) {
         local_survives = true;
+      } else {
+        bool removed = false;
+        if (!process_extra_dir(dirfd, entry->d_name, child_rel, force_now, skips, session,
+                               &removed))
+          operation_ok = false;
+        else if (!removed)
+          local_survives = true;
+      }
+    } else if (rule_protected) {
+      local_survives = true;
     } else {
       if (!process_extra_file(dirfd, entry->d_name, child_rel, force_now, session))
         operation_ok = false;
@@ -833,6 +879,14 @@ int delete_plan_session_receive(DeletePlanSession* session, const Config* config
     }
     session->config_seen = true;
   }
+  /* apply=false is the config-only carrier frame: the receiver consumes the
+     config (and the missing-args exact deletions) but must not walk any
+     directory.  Every real plan carries apply=true. */
+  int apply;
+  if (!receive_int(fd, &apply) || (apply != 0 && apply != 1)) {
+    send_status(fd, STATUS_ERROR);
+    return -1;
+  }
   char* dir = receive_wire_str(fd);
   ArrayList* dirs = array_list_create(free);
   ArrayList* files = array_list_create(free);
@@ -850,7 +904,7 @@ int delete_plan_session_receive(DeletePlanSession* session, const Config* config
   if (!session->dry_run && enabled) {
     if (!session->defer && !apply_missing(session, config))
       ok = false;
-    if (ok && !apply_plan_dir(session, config, dir, dirs, files))
+    if (ok && apply && !apply_plan_dir(session, config, dir, dirs, files))
       ok = false;
   }
   free(dir);

src/shared/delete_plan.h

@@ -48,11 +48,14 @@ void delete_plan_sender_finalize(DeletePlanSender* sender, const ArrayList* sync
    Directory keep entries do not count, so an I/O error that hid every file
    still refuses to delete. */
 bool delete_plan_sender_empty(const DeletePlanSender* sender);
-/* Attach the global config sections advertised on the first plan frame. */
+/* Attach the global config sections advertised on the first plan frame.  The
+ * block is always transmitted by delete_plan_send_root(), on a config-only
+ * carrier frame when the scope allows no directory plan. */
 void delete_plan_sender_set_config(DeletePlanSender* sender, const ArrayList* protected_prefixes,
                                    const ArrayList* size_skipped, const ArrayList* missing_args);
 /* Send the root plan (even before any data, so root extras are handled like
- * rsync's first generator directory).  Returns -1 on I/O error. */
+ * rsync's first generator directory), after transmitting the per-run config
+ * block on its own carrier frame.  Returns -1 on I/O error. */
 int delete_plan_send_root(int fd, DeletePlanSender* sender);
 /* Send the plans for every ancestor of `path` (root-first) and, when is_dir,
  * for `path` itself; already-sent plans are skipped. */

src/shared/file.c

@@ -15,6 +15,7 @@
 #include <unistd.h>
 
 #include "data.h"
+#include "checksum.h"
 #include "delta.h"
 #include "file.h"
 #include "file_store.h"
@@ -24,6 +25,13 @@
 #include "utils.h"
 #include "protocol.h"
 #include "xattr.h"
+#include <fcntl.h>
+#include <unistd.h>
+
+/* Files larger than this are not loaded whole for transfer (the sender streams
+ * them); a whole-file digest is computed from the path instead.  Kept in sync
+ * with the sender's streaming threshold. */
+#define STREAM_THRESHOLD (64ULL * 1024 * 1024)
 
 static bool write_all(int fd, const void* data, unsigned long long size) {
   const unsigned char* p = data;
@@ -39,6 +47,31 @@ static bool write_all(int fd, const void* data, unsigned long long size) {
   return true;
 }
 
+/* Streaming copy of an open source descriptor into the just-created destination
+   `fd` (already at offset 0).  Used by the --copy-dest basis install so a basis
+   larger than any in-memory whole-file bound still materializes without
+   buffering the entire file.  `expected_size` is the caller-verified basis
+   size; the copy must produce exactly that many bytes (a short source is a hard
+   error, never a silently truncated destination).  The final ftruncate drops
+   any residual tail a raced-in longer source might have left. */
+static bool copy_fd_all(int dst_fd, int src_fd, unsigned long long expected_size) {
+  unsigned char buf[1 << 20];
+  unsigned long long done = 0;
+  while (done < expected_size) {
+    unsigned long long remaining = expected_size - done;
+    size_t want = remaining < sizeof(buf) ? (size_t)remaining : sizeof(buf);
+    ssize_t n = read(src_fd, buf, want);
+    if (n < 0 && errno == EINTR)
+      continue;
+    if (n <= 0)
+      return false;
+    if (!write_all(dst_fd, buf, (unsigned long long)n))
+      return false;
+    done += (unsigned long long)n;
+  }
+  return ftruncate(dst_fd, (off_t)expected_size) == 0;
+}
+
 /* Preallocate `size` bytes on `fd` before any data is written (--preallocate).
  * fallocate(2) reserves real disk blocks, so an out-of-space condition
  * (ENOSPC/EDQUOT) surfaces up front instead of partway through a transfer;
@@ -140,6 +173,12 @@ bool file_checksum(File* file, ChecksumAlgo algo, uint64_t seed, uint8_t* out, s
   if (file->data->size == 0) {
     return checksum_digest(algo, seed, "", 0, out, out_capacity, out_len);
   }
+  /* A streamed source (data not loaded) may exceed any in-memory whole-file
+     bound; hash it from the file path in bounded buffers instead of forcing a
+     full load.  This is the same digest the receiver recomputes on the basis. */
+  if (!file->data->data && file->path && file->data->size > STREAM_THRESHOLD &&
+      checksum_digest_file(algo, seed, file->path, out, out_capacity, out_len))
+    return true;
   if (!file->data->data && !file_load_data(file))
     return false;
   return checksum_digest(algo, seed, file->data->data, file->data->size, out, out_capacity,
@@ -176,6 +215,7 @@ File* file_create(const char* path) {
   file->is_dir = false;
   file->dir_time_only = false;
   file->basis_link = NULL;
+  file->basis_copy = NULL;
   file->link_group = 0;
   file->link_first = false;
   file->hardlink_target = NULL;
@@ -205,6 +245,8 @@ void file_destroy(void* item) {
   file->send_path = NULL;
   free(file->basis_link);
   file->basis_link = NULL;
+  free(file->basis_copy);
+  file->basis_copy = NULL;
   free(file->hardlink_target);
   file->hardlink_target = NULL;
   free(file->symlink_target);
@@ -1512,6 +1554,161 @@ bool file_to_disk_secure_attrs_counted(const char* path, const void* data,
  * basis).  Likewise `xattrs`/`fake_super` are applied only on the copy
  * fallback, so a fallback copy preserves the per-file attributes instead of
  * silently dropping them. */
+/* Streaming --copy-dest basis install: atomically materialize `path` from the
+ * bytes of `basis_path` without holding the file in memory, so a basis larger
+ * than any whole-file bound still works.  Mirrors the ordinary secure store
+ * path (confined parent walk, temp + rename, --update/--ignore-existing/
+ * --preallocate/--temp-dir) but sources the data from the basis descriptor
+ * rather than a caller buffer, and applies the SOURCE metadata (rsync copies
+ * then fixes attributes).  A hard-link install that falls back to a byte copy
+ * also routes through here when the caller supplies the basis path. */
+static bool file_copy_basis_stream_impl(const char* path, const char* basis_path,
+                                        unsigned long long expected_size, bool preallocate,
+                                        const FileMetadata* metadata, FileAttrPolicy policy,
+                                        bool update, bool no_replace, bool use_fsync,
+                                        const FileXattrList* xattrs, bool fake_super,
+                                        const char* temp_dir, unsigned* dirs_created,
+                                        const char* count_floor) {
+  if (!path || !basis_path)
+    return false;
+  char* leaf = NULL;
+  int dirfd = file_open_secure_parent_counted(path, &leaf, true, dirs_created, count_floor);
+  if (dirfd < 0)
+    return false;
+
+  char* basis_leaf = NULL;
+  int basis_dirfd = file_open_secure_parent(basis_path, &basis_leaf, false);
+  int src_fd = -1;
+  if (basis_dirfd >= 0 && basis_leaf != NULL) {
+    /* O_NONBLOCK rejects a raced-in FIFO without blocking; the S_ISREG gate
+       below is the real type check. */
+    src_fd = openat(basis_dirfd, basis_leaf, O_RDONLY | O_CLOEXEC | O_NOFOLLOW | O_NONBLOCK);
+    struct stat src_st;
+    if (src_fd >= 0 && (fstat(src_fd, &src_st) != 0 || !S_ISREG(src_st.st_mode))) {
+      close(src_fd);
+      src_fd = -1;
+    }
+  }
+  if (basis_dirfd >= 0)
+    close(basis_dirfd);
+  free(basis_leaf);
+  if (src_fd < 0) {
+    close(dirfd);
+    free(leaf);
+    return false;
+  }
+
+  struct stat destination_stat;
+  bool destination_is_regular = fstatat(dirfd, leaf, &destination_stat, AT_SYMLINK_NOFOLLOW) == 0 &&
+                                S_ISREG(destination_stat.st_mode);
+  if (update && metadata && destination_is_regular && stat_is_newer(&destination_stat, metadata)) {
+    close(src_fd);
+    close(dirfd);
+    free(leaf);
+    return true;
+  }
+  if (no_replace && file_path_exists_secure(path)) {
+    close(src_fd);
+    close(dirfd);
+    free(leaf);
+    return true;
+  }
+
+  int scratch_dirfd = -1;
+  if (temp_dir) {
+    scratch_dirfd = file_open_temp_dir(temp_dir);
+    if (scratch_dirfd < 0) {
+      int saved_errno = errno;
+      log_message(LOG_LEVEL_ERROR,
+                  "--temp-dir '%s' could not be opened (rsync requires it to already exist): %s",
+                  temp_dir, strerror(saved_errno));
+      close(src_fd);
+      close(dirfd);
+      free(leaf);
+      return false;
+    }
+  }
+
+  int target_dirfd = scratch_dirfd >= 0 ? scratch_dirfd : dirfd;
+  int tmp_size = snprintf(NULL, 0, ".%s.tmp.%ld.%llu", leaf, (long)getpid(), ~0ULL);
+  char* tmp = NULL;
+  bool ok = false;
+  if (tmp_size >= 0)
+    tmp = malloc((size_t)tmp_size + 1);
+  if (tmp) {
+    for (unsigned int i = 0; i < 100 && !ok; ++i) {
+      if (scratch_dirfd >= 0)
+        snprintf(tmp, (size_t)tmp_size + 1, ".%s.tmp.%ld.%llu", leaf, (long)getpid(),
+                 next_temp_sequence());
+      else
+        snprintf(tmp, (size_t)tmp_size + 1, ".%s.tmp.%ld.%u", leaf, (long)getpid(), i);
+      int fd =
+          openat(target_dirfd, tmp, O_WRONLY | O_CREAT | O_EXCL | O_CLOEXEC | O_NOFOLLOW, 0600);
+      if (fd < 0) {
+        if (errno != EEXIST)
+          break;
+        continue;
+      }
+      bool wrote = true;
+      if (preallocate && expected_size > 0 && preallocate_fd(fd, expected_size) != 0)
+        wrote = false;
+      if (wrote)
+        wrote = copy_fd_all(fd, src_fd, expected_size);
+      if (wrote && metadata) {
+        if (!policy.perms &&
+            fchmod(fd, file_mode_base(metadata, destination_is_regular,
+                                      destination_is_regular ? destination_stat.st_mode & 0777
+                                                             : 0)) != 0)
+          wrote = false;
+        if (wrote)
+          wrote = file_restore_metadata_fd(fd, metadata, policy);
+      } else if (wrote && fchmod(fd, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH) != 0) {
+        wrote = false;
+      }
+      if (wrote)
+        restore_extra_fd(fd, metadata, xattrs, fake_super, policy);
+      if (wrote && use_fsync)
+        wrote = fsync(fd) == 0;
+      if (close(fd) != 0)
+        wrote = false;
+      if (wrote && renameat(target_dirfd, tmp, dirfd, leaf) != 0)
+        wrote = false;
+      if (!wrote)
+        unlinkat(target_dirfd, tmp, 0);
+      ok = wrote;
+    }
+    free(tmp);
+  }
+  if (!ok && scratch_dirfd >= 0) {
+    /* Retry once with no scratch dir (rsync's EXDEV fallback). */
+    close(scratch_dirfd);
+    close(src_fd);
+    close(dirfd);
+    free(leaf);
+    return file_copy_basis_stream_impl(path, basis_path, expected_size, preallocate, metadata,
+                                       policy, update, no_replace, use_fsync, xattrs, fake_super,
+                                       NULL, dirs_created, count_floor);
+  }
+  if (scratch_dirfd >= 0)
+    close(scratch_dirfd);
+  close(src_fd);
+  close(dirfd);
+  free(leaf);
+  return ok;
+}
+
+/* --copy-dest basis install (streaming).  Applies the source metadata and the
+   per-file xattrs / --fake-super record. */
+bool file_copy_basis_stream_attrs(const char* path, const char* basis_path,
+                                  unsigned long long expected_size, bool preallocate,
+                                  const FileMetadata* metadata, FileAttrPolicy policy, bool update,
+                                  bool use_fsync, const FileXattrList* xattrs, bool fake_super,
+                                  const char* temp_dir) {
+  return file_copy_basis_stream_impl(path, basis_path, expected_size, preallocate, metadata, policy,
+                                     update, false, use_fsync, xattrs, fake_super, temp_dir, NULL,
+                                     NULL);
+}
+
 static bool file_to_disk_secure_link_impl(const char* path, const char* basis_path,
                                           const void* data, unsigned long long data_size,
                                           bool preallocate, const FileMetadata* metadata,
@@ -1521,6 +1718,10 @@ static bool file_to_disk_secure_link_impl(const char* path, const char* basis_pa
                                           const char* count_floor) {
   if (!path || !basis_path)
     return false;
+  /* The caller-supplied buffer is no longer used: the copy fallback streams
+     from the basis path (which may hold an over-limit file).  Kept in the
+     signature for the existing API. */
+  (void)data;
   char* leaf = NULL;
   int dirfd = file_open_secure_parent_counted(path, &leaf, true, dirs_created, count_floor);
   if (dirfd < 0)
@@ -1604,7 +1805,14 @@ static bool file_to_disk_secure_link_impl(const char* path, const char* basis_pa
     close(dirfd);
     free(leaf);
     /* The basis file could not be linked in (missing, cross-device, refused
-       by the filesystem).  Write a byte-identical local copy instead. */
+       by the filesystem).  Stream a byte-identical local copy from the basis
+       itself (never the possibly-absent caller buffer) so an over-limit basis
+       still materializes.  When the basis path is not a readable regular file
+       (e.g. a directory raced in), fall back to the caller-supplied bytes. */
+    if (file_copy_basis_stream_impl(path, basis_path, data_size, preallocate, metadata, policy,
+                                    false, false, use_fsync, xattrs, fake_super, temp_dir,
+                                    dirs_created, count_floor))
+      return true;
     return file_to_disk_secure_attrs_counted(
         path, data, data_size, false, false, preallocate, metadata, policy, false, false, use_fsync,
         xattrs, fake_super, false, temp_dir, dirs_created, count_floor);

src/shared/file.h

@@ -163,6 +163,16 @@ bool file_to_disk_secure_link_attrs(const char* path, const char* basis_path, co
                                     const FileMetadata* metadata, FileAttrPolicy policy,
                                     bool use_fsync, const FileXattrList* xattrs, bool fake_super,
                                     const char* temp_dir);
+/* Streaming --copy-dest install: atomically materialize `path` by copying the
+ * bytes of `basis_path` through a bounded buffer (no whole-file buffering, so
+ * an arbitrarily large basis works), applying the SOURCE metadata and the
+ * per-file xattrs / --fake-super record.  `update` honors a newer destination;
+ * a --temp-dir scratch location falls back to a direct write on EXDEV. */
+bool file_copy_basis_stream_attrs(const char* path, const char* basis_path,
+                                  unsigned long long expected_size, bool preallocate,
+                                  const FileMetadata* metadata, FileAttrPolicy policy, bool update,
+                                  bool use_fsync, const FileXattrList* xattrs, bool fake_super,
+                                  const char* temp_dir);
 /* Protocol 2.28.0 receiver-stat variants: like the two above but additionally
  * report through `dirs_created` (when non-NULL) how many parent directories the
  * confined secure walk had to create that lie strictly below `count_floor` (a

src/shared/file_receive.c

@@ -99,6 +99,12 @@ static FileSaveResult file_stage_delayed_update(const char* root_directory,
   if (file->basis_link) {
     ok = file_to_disk_secure_link(staged_path, file->basis_link, file->data->data, file->data->size,
                                   config->preallocate, metadata, policy, config->use_fsync, NULL);
+  } else if (file->basis_copy) {
+    /* --copy-dest basis hit: stream the basis into the staging tree (bounded
+       buffers, so an over-limit basis still stages). */
+    ok = file_copy_basis_stream_attrs(staged_path, file->basis_copy, file->data->size,
+                                      config->preallocate, metadata, policy, config->update,
+                                      config->use_fsync, file->xattrs, config->fake_super, NULL);
   } else {
     ok =
         file_to_disk_secure_attrs(staged_path, file->data->data, file->data->size, false, sparse,
@@ -652,7 +658,8 @@ FileSaveResult file_save_to_disk_full_ex(const char* root_directory, const File*
   char* destination_path = NULL;
   char *backup_path = NULL, *parent_copy = NULL;
 
-  if (!file || !file->path || !file->data || (file->data->size != 0 && !file->data->data) ||
+  if (!file || !file->path || !file->data ||
+      (file->data->size != 0 && !file->data->data && !file->basis_link && !file->basis_copy) ||
       (!file_get_trust_sender() && has_path_traversal(file->path)) ||
       (backup_enabled &&
        (!backup_suffix || backup_suffix[0] == '\0' || strchr(backup_suffix, '/') != NULL ||
@@ -975,6 +982,13 @@ FileSaveResult file_save_to_disk_full_ex(const char* root_directory, const File*
         disk_path, file->basis_link, file->data->data, file->data->size, config->preallocate,
         metadata, policy, config->use_fsync, file->xattrs, config->fake_super, confined_temp,
         created_dirs, count_floor);
+  } else if (config && file->basis_copy) {
+    /* --copy-dest: stream the basis bytes through a bounded buffer so a basis
+       larger than any whole-file bound still materializes.  The source
+       metadata was transmitted with the check frame. */
+    ok = file_copy_basis_stream_attrs(
+        disk_path, file->basis_copy, file->data->size, config->preallocate, metadata, policy,
+        config->update, config->use_fsync, file->xattrs, config->fake_super, confined_temp);
   } else {
     /* The plain no-replace / update / with-fsync engines, plus per-file xattr
        (-X/-A) and --fake-super application on the written fd. */
@@ -1024,6 +1038,13 @@ void receiver_stats_note_saved(ReceiverStats* stats, const File* file, bool crea
                                unsigned created_dirs) {
   if (!stats || !file)
     return;
+  /* A basis-dir hit (--link-dest/--copy-dest) materializes bytes the sender
+   * never transferred.  rsync reports no literal data and no created entry for
+   * such a file, and does not count the parent directories it creates only to
+   * hold it, so exclude the whole entry from the receiver tallies. */
+  bool basis_sourced = file->basis_link != NULL || file->basis_copy != NULL;
+  if (basis_sourced)
+    return;
   bool is_sibling = file->link_group != 0 && !file->link_first;
   if (!file->is_dir && !file->is_symlink && !file->is_special && !is_sibling) {
     unsigned long long literal = file->literal_bytes;
@@ -1298,16 +1319,17 @@ static File* receive_delta_file(int fd, const Config* config, const char* check_
 
 /* ---- Alternate basis directories (--compare-dest / --copy-dest / --link-dest) ----
  * The receiver consults the ordered basis-dir list only when the destination
- * entry is NOT already up to date.  An "exact match" requires an equal size,
- * an equal mtime (unless --size-only), and an equal content xxHash64, so a
- * hard link / local copy is only ever made from byte-identical content. */
+ * entry is NOT already up to date.  By default an "exact match" is rsync's
+ * metadata quick-check: an equal size and an equal mtime (unless --size-only).
+ * The FastSync-only --verify-basis additionally requires an equal whole-file
+ * content digest, so a hard link / local copy is only then made from
+ * byte-verified content. */
 
 typedef struct BasisMatch {
   bool hit;
   BasisDestType type;
   char* basis_path; /* owned absolute path of the matched basis file */
   struct stat st;   /* fstat() of the matched basis file */
-  Data* content;    /* owned basis bytes (or empty Data), NULL when not loaded */
 } BasisMatch;
 
 static void basis_match_free(BasisMatch* match) {
@@ -1315,8 +1337,6 @@ static void basis_match_free(BasisMatch* match) {
     return;
   free(match->basis_path);
   match->basis_path = NULL;
-  data_destroy(match->content);
-  match->content = NULL;
   match->hit = false;
   match->type = BASIS_DEST_NONE;
 }
@@ -1348,32 +1368,10 @@ static bool basis_open_regular(const char* path, unsigned long long expected_siz
   return true;
 }
 
-/* Read the whole remaining content of an open descriptor.  A zero-length file
-   yields an empty Data (data pointer NULL). */
-static Data* basis_read_content(int fd, unsigned long long size) {
-  if (size == 0)
-    return data_create_reserve(0);
-  if (size > MAX_RECEIVE_WHOLE_FILE_SIZE || size > SIZE_MAX)
-    return NULL;
-  void* buf = protocol_alloc((size_t)size);
-  if (!buf)
-    return NULL;
-  size_t got = 0;
-  while (got < (size_t)size) {
-    ssize_t n = read(fd, (char*)buf + got, (size_t)size - got);
-    if (n <= 0) {
-      free(buf);
-      return NULL;
-    }
-    got += (size_t)n;
-  }
-  return data_create(buf, (size_t)size);
-}
-
 /* --ignore-times forces every file to be updated, so no basis hit is ever
    declared (matching rsync, where -I prevents link-dest from linking). */
-static bool basis_quick_matches(const Config* config, const struct stat* st, time_t check_mtime,
-                                long check_mtime_nsec) {
+bool file_basis_quick_match(const Config* config, const struct stat* st, time_t check_mtime,
+                            long check_mtime_nsec) {
   if (config->size_only)
     return true;
   long mtime_nsec = 0;
@@ -1384,28 +1382,39 @@ static bool basis_quick_matches(const Config* config, const struct stat* st, tim
                                 config->modify_window);
 }
 
-/* Search the basis-dir list in command-line order and return the first exact
-   match.  When load_content is true the matched bytes are kept in out->content
-   so the caller can materialize the file without re-reading it.
+/* True when a basis hit must be confirmed by a whole-file content digest
+   (--verify-basis).  False is the rsync-parity default: the metadata
+   quick-check alone decides a hit. */
+bool file_basis_content_required(const Config* config) {
+  return config != NULL && config->verify_basis;
+}
 
-   An exact match ALSO requires the basis bytes' digest to equal the source's,
-   so `hash_content` gates the content read/hash itself.  A server-contacting
-   --dry-run passes hash_content=false: no basis file may be read or hashed
-   (that would be a 1-bit content oracle against a client-supplied digest), so a
-   metadata-only pass can never confirm a hit and declines it.  The real path
-   always passes hash_content=true, keeping its behavior byte-for-byte. */
+/* Search the basis-dir list in command-line order and return the first match.
+   By default (no --verify-basis) rsync's metadata quick-check is sufficient:
+   basis_open_regular has already required an equal size, and
+   file_basis_quick_match applies rsync's mtime (or --size-only) rule.
+   --verify-basis additionally requires the basis bytes' whole-file digest to
+   equal the sender's, restoring FastSync's historical content equality; that
+   digest is computed by streaming the open basis descriptor, so an arbitrarily
+   large basis is verified without buffering it.  A copy/link install re-reads
+   the basis from its path in bounded buffers, so no content buffer is kept.
+
+   `hash_content` gates content READS under --verify-basis: a server-contacting
+   --dry-run passes false because hashing a basis against a client-supplied
+   digest would be a 1-bit content oracle.  Without --verify-basis a dry-run can
+   still confirm the metadata-only hit without reading any basis bytes, matching
+   rsync's read-only quick-check. */
 static bool basis_match_find(const Config* config, const char* check_path,
                              unsigned long long check_size, time_t check_mtime,
                              long check_mtime_nsec, const uint8_t* check_digest,
-                             size_t check_digest_len, bool load_content, bool hash_content,
-                             BasisMatch* out) {
+                             size_t check_digest_len, bool hash_content, BasisMatch* out) {
   memset(out, 0, sizeof(*out));
   if (!config || !config_has_basis(config) || config->ignore_times)
     return false;
-  /* Dry-run: never read/hash basis content.  A hit cannot be decided from
-     metadata alone, so report no match (the caller treats it as would-transfer)
-     without touching the file's contents. */
-  if (!hash_content)
+  /* --verify-basis needs the basis content; a content-blind (dry-run) pass can
+     never confirm it and must not read the file, so decline without touching
+     the basis bytes. */
+  if (file_basis_content_required(config) && !hash_content)
     return false;
   for (int i = 0; i < config->basis_count; i++) {
     const BasisDest* entry = &config->basis_dirs[i];
@@ -1424,29 +1433,26 @@ static bool basis_match_find(const Config* config, const char* check_path,
     int fd;
     struct stat st;
     if (basis_open_regular(candidate, check_size, &fd, &st)) {
-      if (basis_quick_matches(config, &st, check_mtime, check_mtime_nsec)) {
-        Data* content = basis_read_content(fd, check_size);
-        if (content) {
+      if (file_basis_quick_match(config, &st, check_mtime, check_mtime_nsec)) {
+        bool hit = true;
+        if (file_basis_content_required(config)) {
           uint8_t basis_digest[CHECKSUM_MAX_DIGEST_LEN];
           size_t basis_len = 0;
-          bool hashed = checksum_digest((ChecksumAlgo)config->checksum_algo, config->checksum_seed,
-                                        content->data, content->size, basis_digest,
-                                        sizeof(basis_digest), &basis_len);
-          if (hashed && basis_len == check_digest_len && check_digest_len > 0 &&
-              memcmp(basis_digest, check_digest, check_digest_len) == 0) {
-            out->hit = true;
-            out->type = entry->type;
-            out->basis_path = candidate;
-            candidate = NULL; /* ownership transferred to out */
-            out->st = st;
-            out->content = load_content ? content : NULL;
-            if (!load_content)
-              data_destroy(content);
-            close(fd);
-            return true;
-          }
+          bool hashed =
+              checksum_digest_fd((ChecksumAlgo)config->checksum_algo, config->checksum_seed, fd,
+                                 basis_digest, sizeof(basis_digest), &basis_len);
+          hit = hashed && basis_len == check_digest_len && check_digest_len > 0 &&
+                memcmp(basis_digest, check_digest, check_digest_len) == 0;
+        }
+        if (hit) {
+          out->hit = true;
+          out->type = entry->type;
+          out->basis_path = candidate;
+          candidate = NULL; /* ownership transferred to out */
+          out->st = st;
+          close(fd);
+          return true;
         }
-        data_destroy(content);
       }
       close(fd);
     }
@@ -1871,6 +1877,12 @@ typedef struct {
   long long check_mtime_nsec;
   uint8_t check_digest[CHECKSUM_MAX_DIGEST_LEN];
   size_t check_digest_len;
+  /* Source metadata carried alongside the check frame whenever a basis dir is
+     configured (rsync keeps the whole file list; FastSync's sender-driven
+     incremental path otherwise never transmits metadata for a SKIPPED file).
+     A basis materialization applies these SOURCE attributes instead of the
+     basis inode's, matching rsync's "copy then fix attributes". */
+  FileMetadata* source_metadata;
   bool dest_exists; /* any destination entry exists (lstat succeeded) */
   bool has_old_file;
   int old_fd;
@@ -1903,6 +1915,8 @@ static void incremental_check_state_cleanup(IncrementalCheckState* state) {
   if (state->old_fd >= 0)
     close(state->old_fd);
   state->old_fd = -1;
+  file_metadata_destroy(state->source_metadata);
+  state->source_metadata = NULL;
   free(state->full_path);
   state->full_path = NULL;
   free(state->check_path);
@@ -1927,7 +1941,7 @@ static IncrementalCheckOutcome incremental_check_receive_request(IncrementalChec
     send_error_detail(fd, "invalid check mtime nanoseconds");
     return INCREMENTAL_ERROR;
   }
-  if ((config->checksum || config_has_basis(config))) {
+  if ((config->checksum || config->verify_basis)) {
     uint8_t wire_len;
     if (!receive_n_data(fd, &wire_len, sizeof(wire_len)) || wire_len == 0 ||
         wire_len > CHECKSUM_MAX_DIGEST_LEN ||
@@ -1939,8 +1953,24 @@ static IncrementalCheckOutcome incremental_check_receive_request(IncrementalChec
     if (!receive_n_data(fd, state->check_digest, state->check_digest_len))
       return INCREMENTAL_ERROR;
   }
+  /* The sender transmits the source metadata with every basis-configured check
+     so a basis hit can be materialized with the SOURCE's attributes (rsync
+     copies/copies-then-fixes; the receiver would otherwise only have the basis
+     inode's stat).  The block is symmetric and consumed unconditionally here,
+     whether or not this file ends up as a basis hit. */
+  if (config_has_basis(config) && config->use_metadata) {
+    int meta_ok = 1;
+    state->source_metadata = metadata_receive(fd, &meta_ok);
+    if (!meta_ok)
+      return INCREMENTAL_ERROR;
+  }
 
-  if (state->check_size > MAX_RECEIVE_WHOLE_FILE_SIZE) {
+  /* A basis-configured run may materialize a file larger than the whole-file
+     payload bound: a basis hit is streamed from the basis path (bounded
+     buffers), so the check size is not itself an allocation.  Every other
+     path (delta/append/full) still applies MAX_RECEIVE_WHOLE_FILE_SIZE, and a
+     miss simply falls through to the normal transfer with its own bound. */
+  if (!config_has_basis(config) && state->check_size > MAX_RECEIVE_WHOLE_FILE_SIZE) {
     send_error_detail(fd, "check size exceeds receiver limit");
     return INCREMENTAL_ERROR;
   }
@@ -2030,6 +2060,20 @@ incremental_check_ignore_existing(const IncrementalCheckState* state) {
   return INCREMENTAL_SKIP;
 }
 
+/* Metadata for a materialized basis hit: prefer the SOURCE metadata the sender
+   transmitted with the check frame (rsync copies then fixes the destination to
+   the source's attributes); fall back to the basis inode's own stat when
+   metadata was not negotiated.  Consumes state->source_metadata on success. */
+static FileMetadata* basis_take_metadata(IncrementalCheckState* state,
+                                         const struct stat* basis_st) {
+  if (state->source_metadata) {
+    FileMetadata* meta = state->source_metadata;
+    state->source_metadata = NULL;
+    return meta;
+  }
+  return file_metadata_create(NULL, basis_st, false, false);
+}
+
 /* --link-dest relink of an already up-to-date destination.  rsync hard-links a
    destination entry to a matching basis even when the entry is already correct,
    so a run over an existing tree still maximizes sharing with the basis.  Only a
@@ -2047,7 +2091,7 @@ static IncrementalCheckOutcome incremental_check_link_dest_relink(IncrementalChe
   BasisMatch basis;
   basis_match_find(config, state->check_path, state->check_size, (time_t)state->check_mtime,
                    (long)state->check_mtime_nsec, state->check_digest, state->check_digest_len,
-                   true, true, &basis);
+                   true, &basis);
   /* Only a link-dest hit relinks; a copy-dest/compare-dest hit (or a miss) lets
      the up-to-date check below keep the existing destination. */
   if (!basis.hit || basis.type != BASIS_DEST_LINK) {
@@ -2060,11 +2104,16 @@ static IncrementalCheckOutcome incremental_check_link_dest_relink(IncrementalChe
     return INCREMENTAL_CONTINUE;
   }
   File* materialized = file_create(state->check_path);
-  if (materialized && basis.content) {
+  if (materialized) {
     data_destroy(materialized->data);
-    materialized->data = basis.content;
-    basis.content = NULL;
-    materialized->metadata = file_metadata_create(NULL, &basis.st, false, false);
+    materialized->data = data_create_reserve((size_t)state->check_size);
+    if (!materialized->data) {
+      file_destroy(materialized);
+      materialized = NULL;
+    }
+  }
+  if (materialized) {
+    materialized->metadata = basis_take_metadata(state, &basis.st);
     materialized->skip = true;
     materialized->basis_link = basis.basis_path;
     basis.basis_path = NULL;
@@ -2072,9 +2121,6 @@ static IncrementalCheckOutcome incremental_check_link_dest_relink(IncrementalChe
       file_destroy(materialized);
       materialized = NULL;
     }
-  } else {
-    file_destroy(materialized);
-    materialized = NULL;
   }
   if (materialized) {
     if (!send_status(state->fd, STATUS_OK)) {
@@ -2175,12 +2221,13 @@ static IncrementalCheckOutcome incremental_check_quick_skip(IncrementalCheckStat
    materialize nothing (no basis link/copy, no append/delta/full transfer) and
    the sender must send no data, so answer STATUS_DRY_RUN_TRANSFER and stop.
 
-   The basis lookup is deliberately content-blind: a real run would only accept
-   a --compare-dest exact hit after hashing the basis file and comparing it with
-   the client-supplied digest, which in a dry-run is a 1-bit content oracle.
-   Under dry_run no basis bytes may be read, so an otherwise-matching entry is
-   treated as would-transfer instead of a skip.  Everything read here (the
-   destination file's metadata, basis candidates' metadata) is read-only. */
+   The basis lookup is content-blind: under the default metadata quick-check a
+   hit needs no basis bytes and is honored here just as in a real run; under
+   --verify-basis a real run hashes the basis against the client-supplied digest,
+   which in a dry-run is a 1-bit content oracle, so no basis bytes may be read
+   and an otherwise-matching entry is reported as would-transfer.  Everything
+   read here (the destination file's metadata, basis candidates' metadata) is
+   read-only. */
 static IncrementalCheckOutcome incremental_check_dry_run_shortcut(IncrementalCheckState* state,
                                                                   bool* skipped,
                                                                   bool* would_transfer) {
@@ -2191,12 +2238,14 @@ static IncrementalCheckOutcome incremental_check_dry_run_shortcut(IncrementalChe
   bool skip_via_compare = false;
   if (config_has_basis(config) && !config->ignore_times) {
     BasisMatch basis;
-    /* hash_content=false: a dry-run must not read or hash the basis file.  No
-       content comparison is possible, so no compare-dest hit can be confirmed
-       and an otherwise-matching file is reported as would-transfer. */
+    /* hash_content=false: a dry-run must not read or hash the basis file, so
+       under --verify-basis no compare-dest hit can be confirmed and an
+       otherwise-matching file is reported as would-transfer.  Without
+       --verify-basis the metadata quick-check confirms it without touching any
+       basis bytes. */
     basis_match_find(config, state->check_path, state->check_size, (time_t)state->check_mtime,
                      (long)state->check_mtime_nsec, state->check_digest, state->check_digest_len,
-                     false, false, &basis);
+                     false, &basis);
     if (basis.hit && basis.type == BASIS_DEST_COMPARE && !state->has_old_file)
       skip_via_compare = true;
     basis_match_free(&basis);
@@ -2224,7 +2273,7 @@ static IncrementalCheckOutcome incremental_check_try_basis(IncrementalCheckState
   BasisMatch basis;
   basis_match_find(config, state->check_path, state->check_size, (time_t)state->check_mtime,
                    (long)state->check_mtime_nsec, state->check_digest, state->check_digest_len,
-                   true, true, &basis);
+                   true, &basis);
   if (basis.hit) {
     if (basis.type == BASIS_DEST_COMPARE) {
       basis_match_free(&basis);
@@ -2234,24 +2283,30 @@ static IncrementalCheckOutcome incremental_check_try_basis(IncrementalCheckState
         return INCREMENTAL_SKIP;
       }
     } else {
+      /* Copy/link installs source their bytes from the basis PATH at install
+         time (bounded buffers), so no whole-file content buffer is needed here
+         even for an over-limit basis. */
       File* materialized = file_create(state->check_path);
-      if (materialized && basis.content) {
+      if (materialized) {
         data_destroy(materialized->data);
-        materialized->data = basis.content;
-        basis.content = NULL;
-        materialized->metadata = file_metadata_create(NULL, &basis.st, false, false);
-        materialized->skip = true; /* receiver must not ack this as a data file */
-        if (basis.type == BASIS_DEST_LINK) {
-          materialized->basis_link = basis.basis_path;
-          basis.basis_path = NULL;
+        materialized->data = data_create_reserve((size_t)state->check_size);
+        if (!materialized->data) {
+          file_destroy(materialized);
+          materialized = NULL;
         }
+      }
+      if (materialized) {
+        materialized->metadata = basis_take_metadata(state, &basis.st);
+        materialized->skip = true; /* receiver must not ack this as a data file */
+        if (basis.type == BASIS_DEST_LINK)
+          materialized->basis_link = basis.basis_path;
+        else
+          materialized->basis_copy = basis.basis_path;
+        basis.basis_path = NULL;
         if (!materialized->metadata) {
           file_destroy(materialized);
           materialized = NULL;
         }
-      } else {
-        file_destroy(materialized);
-        materialized = NULL;
       }
       if (materialized) {
         if (!send_status(fd, STATUS_OK)) {
@@ -3328,7 +3383,7 @@ static bool delete_extras_budgeted_observed(const Config* config, DeleteManifest
   size_t skipped = 0;
   DeleteWalkResult result = delete_extras_limited_observed(
       config->receive_root_directory, manifest->keeps, manifest->dirs, remaining, skips, used,
-      &deleted, &skipped, observer, observer_context);
+      config->protect_rules, &deleted, &skipped, observer, observer_context);
   if (owned_prefixes) {
     for (int i = 0; i < config->basis_count; i++)
       free(owned_prefixes[i]);
@@ -3509,7 +3564,7 @@ static bool delete_missing_args_budgeted_observed(const Config* config, DeleteMa
           PrefixedDeleteObserver nested = {observer, observer_context, rel};
           DeleteWalkResult walk =
               no_keeps ? delete_extras_limited_observed(full, no_keeps, NULL, remaining, NULL, 0,
-                                                        &contents_deleted, &contents_skipped,
+                                                        NULL, &contents_deleted, &contents_skipped,
                                                         observer ? prefixed_delete_observer : NULL,
                                                         observer ? &nested : NULL)
                        : DELETE_WALK_ERROR;
@@ -3620,7 +3675,7 @@ bool manifest_would_delete_list(const Config* config, DeleteManifest* manifest,
     used = idx;
   }
   bool ok = delete_extras_list(config->receive_root_directory, manifest->keeps, manifest->dirs,
-                               skips, used, out, count_out);
+                               skips, used, config->protect_rules, out, count_out);
   if (owned_prefixes) {
     for (int i = 0; i < config->basis_count; i++)
       free(owned_prefixes[i]);

src/shared/file_receive.h

@@ -24,6 +24,16 @@ File* file_receive_hardlink(int file_descriptor);
 File* file_receive_symlink(int file_descriptor, const Config* config);
 File* file_receive_special(int file_descriptor);
 bool file_special_rdev_valid(int32_t major, int32_t minor, mode_t mode);
+/* Testable basis quick-check / verification policy.  file_basis_quick_match is
+ * rsync's metadata quick-check for a basis candidate (equal size is required
+ * separately by the caller; this adds the --size-only / mtime / --modify-window
+ * leg).  file_basis_content_required reports whether a hit must ALSO be
+ * confirmed by a whole-file content digest (--verify-basis; false is the
+ * default rsync-parity behavior). */
+bool file_basis_quick_match(const Config* config, const struct stat* st, time_t check_mtime,
+                            long check_mtime_nsec);
+bool file_basis_content_required(const Config* config);
+
 File* receive_incremental_check(int fd, const Config* config, bool* skipped);
 /* Extended variant used by the receiver.  `would_transfer` (may be NULL) is set
  * true only on the server-contacting --dry-run path when the file is not up to

src/shared/file_types.h

@@ -57,6 +57,11 @@ typedef struct {
    * equals the incoming file, and `data` is kept as the cross-filesystem
    * fallback (a local copy) if the hard link cannot be created. */
   char* basis_link;
+  /* Receiver-only, --copy-dest: when set (and basis_link is NULL), stream the
+   * basis file's bytes into the destination instead of `data`/`data->size`.
+   * This lets a basis larger than any whole-file bound materialize without
+   * buffering it; the source metadata on `metadata` is applied afterwards. */
+  char* basis_copy;
   /* --hard-links (-H), sender + receiver wire state.  link_group is a run-local
    * id shared by every member of one source inode (0 = not part of a group).
    * The FIRST member (link_first == true) carries its data on the wire and is

src/shared/filter.h

@@ -53,7 +53,7 @@ typedef struct {
   char* pattern;       /* cleaned glob pattern (no leading '/', no trailing '/') */
 } FilterRule;
 
-typedef struct {
+typedef struct FilterRuleList {
   FilterRule** items; /* owned array of rule pointers */
   int count;
   int capacity;

src/shared/protocol.h

@@ -191,7 +191,9 @@ enum NET_STATUS {
    * (--delete-delay).  Payload: an int32 has_config flag (1 on the first plan
    * of the run, 0 afterwards); when set, the three global config sections
    * (protected-prefix count+paths, size-skipped count+paths, missing-args
-   * count+paths); then the destination-relative directory path wire string
+   * count+paths); then an int32 apply flag (1 for a real plan, 0 for a
+   * config-only carrier frame that must not walk a directory); then the
+   * destination-relative directory path wire string
    * ("." for the receive root); then the child-directory count + names and the
    * child-file count + names that must be kept.  Appended after
    * STATUS_DEST_INFO so no existing status is renumbered. */

src/shared/utils.c

@@ -682,7 +682,8 @@ static bool is_synced_dir(const PathIndex* dirs, const char* rel) {
    like any other non-directory extra (never followed). */
 static bool delete_extras_fd(int dirfd, const char* rel_path, const PathIndex* keep,
                              const PathIndex* dirs, DeleteBudget* budget,
-                             const DeleteSkipEntry* skips, int skip_count, bool parent_deletable,
+                             const DeleteSkipEntry* skips, int skip_count,
+                             const FilterRuleList* protect_rules, bool parent_deletable,
                              bool* all_removed, DeletePathObserver observer,
                              void* observer_context) {
   /* openat(dirfd, ".") opens an independent file description: a dup() would
@@ -729,12 +730,23 @@ static bool delete_extras_fd(int dirfd, const char* rel_path, const PathIndex* k
       free(child_rel);
       continue;
     }
-    if (S_ISDIR(st.st_mode)) {
+    bool is_dir = S_ISDIR(st.st_mode);
+    if (protect_rules && filter_rules_apply_side(protect_rules, child_rel, entry->d_name, is_dir,
+                                                 FILTER_SIDE_RECEIVER) == FILTER_ACTION_PROTECT) {
+      /* A first-match protect rule shields the extra; for a directory the whole
+         subtree is shielded (rsync prunes an excluded directory), so do not
+         descend. */
+      local_survives = true;
+      free(child_rel);
+      continue;
+    }
+    if (is_dir) {
       int childfd = openat(dirfd, entry->d_name, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
       bool child_all_removed = false;
       if (childfd >= 0) {
-        if (!delete_extras_fd(childfd, child_rel, keep, dirs, budget, skips, skip_count, deletable,
-                              &child_all_removed, observer, observer_context))
+        if (!delete_extras_fd(childfd, child_rel, keep, dirs, budget, skips, skip_count,
+                              protect_rules, deletable, &child_all_removed, observer,
+                              observer_context))
           operation_ok = false;
         close(childfd);
       } else if (errno != ENOENT) {
@@ -802,7 +814,8 @@ static bool delete_extras_fd(int dirfd, const char* rel_path, const PathIndex* k
    reportable children (depth-first), matching the delete pass's ordering. */
 static bool list_extras_fd(int dirfd, const char* rel_path, const PathIndex* keep,
                            const PathIndex* dirs, ArrayList* out, size_t* recorded,
-                           const DeleteSkipEntry* skips, int skip_count, bool parent_deletable,
+                           const DeleteSkipEntry* skips, int skip_count,
+                           const FilterRuleList* protect_rules, bool parent_deletable,
                            bool* all_removed) {
   int scanfd = openat(dirfd, ".", O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
   if (scanfd < 0)
@@ -836,12 +849,21 @@ static bool list_extras_fd(int dirfd, const char* rel_path, const PathIndex* kee
       free(child_rel);
       continue;
     }
-    if (S_ISDIR(st.st_mode)) {
+    bool is_dir = S_ISDIR(st.st_mode);
+    if (protect_rules && filter_rules_apply_side(protect_rules, child_rel, entry->d_name, is_dir,
+                                                 FILTER_SIDE_RECEIVER) == FILTER_ACTION_PROTECT) {
+      /* Mirror the delete walk: a protected entry is never reported as a
+         would-delete and a protected directory's subtree is not enumerated. */
+      local_survives = true;
+      free(child_rel);
+      continue;
+    }
+    if (is_dir) {
       int childfd = openat(dirfd, entry->d_name, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
       bool child_all_removed = false;
       if (childfd >= 0) {
         if (!list_extras_fd(childfd, child_rel, keep, dirs, out, recorded, skips, skip_count,
-                            deletable, &child_all_removed))
+                            protect_rules, deletable, &child_all_removed))
           operation_ok = false;
         close(childfd);
       } else if (errno != ENOENT) {
@@ -892,7 +914,7 @@ static bool list_extras_fd(int dirfd, const char* rel_path, const PathIndex* kee
 
 bool delete_extras_list(const char* dest_root, const ArrayList* manifest,
                         const ArrayList* synced_dirs, const DeleteSkipEntry* skips, int skip_count,
-                        ArrayList* out, size_t* count_out) {
+                        const FilterRuleList* protect_rules, ArrayList* out, size_t* count_out) {
   if (count_out)
     *count_out = 0;
   if (!manifest || !out)
@@ -928,7 +950,7 @@ bool delete_extras_list(const char* dest_root, const ArrayList* manifest,
   bool all_removed = false;
   size_t recorded = 0;
   bool ok = list_extras_fd(rootfd, "", &keep, have_dirs ? &dirs : NULL, out, &recorded, skips,
-                           skip_count, false, &all_removed);
+                           skip_count, protect_rules, false, &all_removed);
   if (close(rootfd) != 0)
     ok = false;
   path_index_free(&keep);
@@ -942,6 +964,7 @@ bool delete_extras_list(const char* dest_root, const ArrayList* manifest,
 DeleteWalkResult delete_extras_limited_observed(const char* dest_root, const ArrayList* manifest,
                                                 const ArrayList* synced_dirs, size_t max_delete,
                                                 const DeleteSkipEntry* skips, int skip_count,
+                                                const FilterRuleList* protect_rules,
                                                 size_t* deleted_out, size_t* skipped_out,
                                                 DeletePathObserver observer,
                                                 void* observer_context) {
@@ -984,8 +1007,9 @@ DeleteWalkResult delete_extras_limited_observed(const char* dest_root, const Arr
   }
   DeleteBudget budget = {.max_delete = max_delete, .deleted = 0, .skipped = 0, .limit_hit = false};
   bool all_removed = false;
-  bool ok = delete_extras_fd(rootfd, "", &keep, have_dirs ? &dirs : NULL, &budget, skips,
-                             skip_count, false, &all_removed, observer, observer_context);
+  bool ok =
+      delete_extras_fd(rootfd, "", &keep, have_dirs ? &dirs : NULL, &budget, skips, skip_count,
+                       protect_rules, false, &all_removed, observer, observer_context);
   if (close(rootfd) != 0)
     ok = false;
   path_index_free(&keep);
@@ -1003,13 +1027,15 @@ DeleteWalkResult delete_extras_limited_observed(const char* dest_root, const Arr
 DeleteWalkResult delete_extras_limited(const char* dest_root, const ArrayList* manifest,
                                        const ArrayList* synced_dirs, size_t max_delete,
                                        const DeleteSkipEntry* skips, int skip_count,
-                                       size_t* deleted_out, size_t* skipped_out) {
+                                       const FilterRuleList* protect_rules, size_t* deleted_out,
+                                       size_t* skipped_out) {
   return delete_extras_limited_observed(dest_root, manifest, synced_dirs, max_delete, skips,
-                                        skip_count, deleted_out, skipped_out, NULL, NULL);
+                                        skip_count, protect_rules, deleted_out, skipped_out, NULL,
+                                        NULL);
 }
 
 bool delete_extras(const char* dest_root, const ArrayList* manifest) {
-  return delete_extras_limited(dest_root, manifest, NULL, SIZE_MAX, NULL, 0, NULL, NULL) ==
+  return delete_extras_limited(dest_root, manifest, NULL, SIZE_MAX, NULL, 0, NULL, NULL, NULL) ==
          DELETE_WALK_OK;
 }
 

src/shared/utils.h

@@ -2,6 +2,7 @@
 #define UTILS_H
 
 #include "array_list.h"
+#include "filter.h"
 #include <stddef.h>
 #include <stdbool.h>
 #include <stdio.h>
@@ -148,7 +149,8 @@ bool path_under_skip_prefix(const char* child_rel, bool at_root, const DeleteSki
 DeleteWalkResult delete_extras_limited(const char* dest_root, const ArrayList* manifest,
                                        const ArrayList* synced_dirs, size_t max_delete,
                                        const DeleteSkipEntry* skips, int skip_count,
-                                       size_t* deleted_out, size_t* skipped_out);
+                                       const FilterRuleList* protect_rules, size_t* deleted_out,
+                                       size_t* skipped_out);
 
 /* Optional per-deletion observer: called for each destination-relative path
    actually removed (a file, symlink, or directory), in removal order, so the
@@ -156,10 +158,15 @@ DeleteWalkResult delete_extras_limited(const char* dest_root, const ArrayList* m
 typedef void (*DeletePathObserver)(void* context, const char* rel_path);
 
 /* `delete_extras_limited_observed` is delete_extras_limited with an optional
-   observer; the observer is invoked only for entries truly removed. */
+ * observer; the observer is invoked only for entries truly removed.  When
+ * `protect_rules` is non-NULL its receiver-side verdict is evaluated for every
+ * candidate extra: a first-match PROTECT leaves the entry (and, for a
+ * directory, its whole subtree) in place, while RISK/NONE fall through to the
+ * ordinary skip-prefix/keep-set logic. */
 DeleteWalkResult delete_extras_limited_observed(const char* dest_root, const ArrayList* manifest,
                                                 const ArrayList* synced_dirs, size_t max_delete,
                                                 const DeleteSkipEntry* skips, int skip_count,
+                                                const FilterRuleList* protect_rules,
                                                 size_t* deleted_out, size_t* skipped_out,
                                                 DeletePathObserver observer,
                                                 void* observer_context);
@@ -170,7 +177,7 @@ DeleteWalkResult delete_extras_limited_observed(const char* dest_root, const Arr
    strings appended to `out` and receives their count in *count_out. */
 bool delete_extras_list(const char* dest_root, const ArrayList* manifest,
                         const ArrayList* synced_dirs, const DeleteSkipEntry* skips, int skip_count,
-                        ArrayList* out, size_t* count_out);
+                        const FilterRuleList* protect_rules, ArrayList* out, size_t* count_out);
 bool delete_extras(const char* dest_root, const ArrayList* manifest);
 /* Open the existing destination directory at `dest_root`, confined to the
    authorized root with an O_NOFOLLOW component walk (the same confinement the

tests/fuzz/fuzz_config_receive.c

@@ -119,6 +119,13 @@ static void build_canonical_frame(void) {
     cfg->usermap[0].to = MAP_TO;
     cfg->usermap[0].to_name = NULL;
   }
+  /* Force a non-empty receiver delete-protection block so the fuzzer mutates
+   * its rule count, action/sides codes and pattern strings. */
+  cfg->filters = array_list_create(free);
+  if (cfg->filters) {
+    array_list_add(cfg->filters, str_dup("P *.log"));
+    array_list_add(cfg->filters, str_dup("+r keep/**"));
+  }
   if (!cfg->send_directory || !cfg->receive_root_directory || !cfg->usermap) {
     config_delete(cfg);
     return;

tests/integration/parity_harness.py

@@ -229,6 +229,18 @@ def corpus_iconv(root: str) -> None:
         os.utime(full, (_SRC_MTIME, _SRC_MTIME))
 
 
+# Payload for the --fuzzy basis corpus: large enough for the delta engine's
+# 16 KiB minimum and with repeated content so a coinciding basis yields a
+# non-zero (and identical) Matched data count in both tools.
+FUZZY_PAYLOAD = (b"the quick brown fox jumps over the lazy dog\n" * 2000)[:65536]
+
+
+def corpus_fuzzy(root: str) -> None:
+    """A named regular file; the `fuzzy` seed adds the similar-suffix sibling."""
+    clean_dir(root)
+    _write(os.path.join(root, "report_v2.txt"), FUZZY_PAYLOAD)
+
+
 CORPORA: Dict[str, Callable[[str], None]] = {
     "basic": corpus_basic,
     "unicode": corpus_unicode,
@@ -240,6 +252,7 @@ CORPORA: Dict[str, Callable[[str], None]] = {
     "multidir": corpus_multidir,
     "relative": corpus_relative,
     "iconv": corpus_iconv,
+    "fuzzy": corpus_fuzzy,
 }
 
 

tests/integration/test_codecs.py

@@ -9,6 +9,7 @@ directory when the shared test server is launched), so every scratch tree lives
 under ``TEST_DATA_DIR`` rather than pytest's ``tmp_path``.
 """
 import os
+import random
 import shutil
 import subprocess
 import sys
@@ -68,6 +69,84 @@ def _tree_bytes(root):
     return out
 
 
+_CC_DELTA_T0 = 1_600_000_000
+_CC_DELTA_T1 = 1_600_000_100
+
+_DELTA_STATS_KEYS = (
+    "Number of created files",
+    "Number of regular files transferred",
+    "Total transferred file size",
+    "Literal data",
+    "Matched data",
+)
+
+
+def _pin_tree(root, mtime):
+    for dirpath, dirnames, filenames in os.walk(root):
+        for name in dirnames + filenames:
+            path = os.path.join(dirpath, name)
+            if not os.path.islink(path):
+                os.utime(path, (mtime, mtime))
+    os.utime(root, (mtime, mtime))
+
+
+def _make_delta_basis(src, size=512 * 1024):
+    """Build a source and a matching pre-modification basis tree.
+
+    The source's ``big.bin`` is then modified in a few disjoint places and given
+    a newer mtime so both tools take the delta path.  Returns the basis dir.
+    """
+    clean_dir(src)
+    original = random.Random(20240101).randbytes(size)
+    with open(os.path.join(src, "big.bin"), "wb") as fh:
+        fh.write(original)
+    with open(os.path.join(src, "small.txt"), "wb") as fh:
+        fh.write(b"hello world\n")
+    _pin_tree(src, _CC_DELTA_T0)
+
+    basis = src.rstrip("/") + "_basis"
+    clean_dir(basis)
+    shutil.copy2(os.path.join(src, "big.bin"), os.path.join(basis, "big.bin"))
+    shutil.copy2(os.path.join(src, "small.txt"), os.path.join(basis, "small.txt"))
+    _pin_tree(basis, _CC_DELTA_T0)
+
+    modified = bytearray(original)
+    for off in (0, size // 3, 2 * size // 3, size - 64):
+        for i in range(32):
+            modified[off + i] ^= 0x5A
+    with open(os.path.join(src, "big.bin"), "wb") as fh:
+        fh.write(bytes(modified))
+    os.utime(os.path.join(src, "big.bin"), (_CC_DELTA_T1, _CC_DELTA_T1))
+    return basis
+
+
+def _seed_from_basis(basis, target):
+    clean_dir(target)
+    for name in os.listdir(basis):
+        shutil.copy2(os.path.join(basis, name), os.path.join(target, name))
+
+
+def _delta_stats(text):
+    found = {}
+    for line in text.splitlines():
+        for key in _DELTA_STATS_KEYS:
+            if line.startswith(key + ":"):
+                found[key] = line.split(":", 1)[1].strip()
+    return found
+
+
+def _big_bin_outfmt(text):
+    """The ``(c, C)`` pair from the ``big.bin`` out-format line (`%c|%C %n`)."""
+    for line in text.splitlines():
+        stripped = line.strip()
+        if "|" not in stripped or not stripped.endswith("big.bin"):
+            continue
+        c_field, rest = stripped.split("|", 1)
+        fields = rest.split()
+        return c_field.strip(), (fields[0] if fields else "")
+    return None, None
+
+
 class TestCodecChoiceMatrix:
     """The CLI accept/reject set and exit codes must match rsync 3.4.1."""
 
@@ -191,6 +270,76 @@ class TestCodecTransferDifferential:
         assert _tree_bytes(received) == _tree_bytes(rsync_dst)
 
 
+class TestChecksumChoiceDeltaSurface:
+    """--checksum-choice does not move the delta-transfer parity surface.
+
+    FastSync's delta BLOCK strong checksum is a fixed xxHash32, so the
+    negotiated algorithm only selects the whole-file comparison digest (and the
+    ``%C`` transfer digest).  A pre-seeded delta transfer must therefore land
+    byte-identical bytes and report the same counters for every choice, while
+    ``%C`` -- the one token that tracks the choice -- stays byte-identical to
+    rsync.  This pins the Track-3b reclassification in RSYNC_COMPAT.md.
+    """
+
+    CHOICES = ["xxh64", "xxh128", "xxh3", "md5", "md4", "sha1",
+               "xxh64,sha1", "sha1,xxh64"]
+
+    @requires_rsync
+    @pytest.mark.ci
+    def test_delta_surface_invariant_to_checksum_choice(self, shared_server):
+        src = _scratch("ccdelta_src")
+        basis = _make_delta_basis(src)
+        source_bytes = _tree_bytes(src)
+
+        rsync_c, fastsync_c, digests = {}, {}, {}
+        rsync_stats, fastsync_stats = {}, {}
+        for choice in self.CHOICES:
+            tag = choice.replace(",", "_")
+            rsync_dst = _scratch(f"ccdelta_rs_{tag}")
+            fs_dst = _scratch(f"ccdelta_fs_{tag}")
+            fs_root = get_dest_received_dir(fs_dst, src)
+            _seed_from_basis(basis, rsync_dst)
+            _seed_from_basis(basis, fs_root)
+
+            # Pin the block size on both ends so the literal/matched split is
+            # comparable (rsync's adaptive default would otherwise differ from
+            # FastSync's 8192-byte default).
+            rsync_result = _rsync(["-a", "--no-whole-file", "-B8192", "--stats",
+                                   "--out-format=%c|%C %n", f"--cc={choice}",
+                                   src + "/", rsync_dst + "/"])
+            assert rsync_result.returncode == 0, rsync_result.stderr
+            result, _ = run_client(
+                src, fs_dst,
+                flags=["-a", "--incremental", "--delta", "-B8192", "--stats",
+                       "--out-format=%c|%C %n", f"--cc={choice}"],
+                port=shared_server.port)
+            assert result.returncode == 0, (result.stderr or result.stdout)[:300]
+
+            assert _tree_bytes(rsync_dst) == source_bytes, choice
+            assert _tree_bytes(fs_root) == source_bytes, choice
+            assert _delta_stats(rsync_result.stdout) == _delta_stats(result.stdout), choice
+
+            rs_c, rs_C = _big_bin_outfmt(rsync_result.stdout)
+            fs_c, fs_C = _big_bin_outfmt(result.stdout)
+            assert rs_C == fs_C, f"{choice}: %C rsync={rs_C!r} fastsync={fs_C!r}"
+            rsync_c[choice] = rs_c
+            fastsync_c[choice] = fs_c
+            digests[choice] = fs_C
+            rsync_stats[choice] = _delta_stats(rsync_result.stdout)
+            fastsync_stats[choice] = _delta_stats(result.stdout)
+
+        # The choice is only observable in %C, and it is effective (the digests
+        # are not all the same algorithm's output).
+        assert len(set(digests.values())) > 1, digests
+        # The compared --stats counters are invariant across choices in each tool
+        # (and were asserted equal cross-tool inside the loop).
+        assert len({tuple(sorted(s.items())) for s in rsync_stats.values()}) == 1, rsync_stats
+        assert len({tuple(sorted(s.items())) for s in fastsync_stats.values()}) == 1, fastsync_stats
+        # The block-checksum token (%c) is invariant across choices in each tool.
+        assert len(set(rsync_c.values())) == 1, rsync_c
+        assert len(set(fastsync_c.values())) == 1, fastsync_c
+
+
 class TestCodecNegotiationFallback:
     """FastSync's auto negotiation and deterministic fallback order."""
 

tests/integration/test_delete_timing_parity.py

@@ -217,7 +217,21 @@ class _SlicingProxy:
 
 
 class TestDeleteTimingFinalStateParity:
-    """On a successful transfer the per-directory timings match rsync's result."""
+    """On a successful transfer the per-directory timings match rsync's result.
+
+    Plain ``--delete`` has no rsync-incompatible spelling: it defaults to
+    delete-during on both tools, so it is compared against rsync's own default.
+    ``--delete-commit`` is FastSync-only and selects the late whole-tree commit,
+    which is rsync's ``--delete-after`` timing.
+    """
+
+    # (fastsync flag, rsync flag)
+    PAIRS = [
+        ("--delete", "--delete"),
+        ("--delete-during", "--delete-during"),
+        ("--delete-delay", "--delete-delay"),
+        ("--delete-commit", "--delete-after"),
+    ]
 
     def _run_fastsync(self, tag, timing):
         source, dest, received = _seed_pair(tag)
@@ -226,12 +240,12 @@ class TestDeleteTimingFinalStateParity:
             result, _ = run_client(source, dest, flags=[timing], port=server.port)
         return result, received
 
-    @pytest.mark.parametrize("timing", ["--delete-during", "--delete-delay"])
+    @pytest.mark.parametrize("fs_timing,rs_timing", PAIRS)
     @requires_rsync
-    def test_success_final_state_matches_rsync(self, timing):
-        # Worker-safe names: xdist may run both parametrizations concurrently, so
-        # the timing is part of every fixture path.
-        label = timing.lstrip("-")
+    def test_success_final_state_matches_rsync(self, fs_timing, rs_timing):
+        # Worker-safe names: xdist may run the parametrizations concurrently, so
+        # the flags are part of every fixture path.
+        label = f"{fs_timing.lstrip('-')}_vs_{rs_timing.lstrip('-')}"
         # Build the rsync fixture from the same seed so both sides start equal.
         source, dest, received = _seed_pair(f"parity_rsync_{label}")
         source2 = source
@@ -240,17 +254,18 @@ class TestDeleteTimingFinalStateParity:
         # rsync mirrors src/ into dst/; seed the same extra.
         _write(os.path.join(rsync_dst, "d", "old_extra"), b"stale extra\n")
 
-        rsync_result = _rsync(["-a", timing, source2 + "/", rsync_dst + "/"])
+        rsync_result = _rsync(["-a", rs_timing, source2 + "/", rsync_dst + "/"])
         assert rsync_result.returncode == 0, rsync_result.stderr
         rsync_tree = _tree(rsync_dst)
 
         with ServerManager() as server:
             server.start(extra_args=["--allow-delete"])
-            result, _ = run_client(source, dest, flags=[timing], port=server.port)
+            result, _ = run_client(source, dest, flags=[fs_timing], port=server.port)
         assert result.returncode == 0, (result.stderr or result.stdout)[:300]
         fastsync_tree = _tree(received)
         assert fastsync_tree == rsync_tree, (
-            f"{timing}: fastsync tree {fastsync_tree} != rsync tree {rsync_tree}"
+            f"{fs_timing} vs rsync {rs_timing}: fastsync tree {fastsync_tree} != "
+            f"rsync tree {rsync_tree}"
         )
 
 
@@ -292,7 +307,14 @@ class TestDeleteTimingTypeConflictParity:
 
 
 class TestDeleteTimingFailure:
-    """A mid-transfer failure distinguishes during from delay."""
+    """A mid-transfer failure distinguishes the during timings from the late
+    commit timings.
+
+    Plain ``--delete`` must behave like ``--delete-during`` (the rsync default),
+    removing the extras of the directories already reached; ``--delete-commit``
+    must behave like ``--delete-after`` and remove nothing until the transfer
+    has fully succeeded.
+    """
 
     @pytest.mark.parametrize("mt", [False, True])
     def test_during_removes_delay_preserves_on_failure(self, mt):
@@ -301,8 +323,12 @@ class TestDeleteTimingFailure:
         assert os.path.exists(extra)
         with ServerManager() as server:
             server.start(extra_args=["--allow-delete"])
-            for timing, expect_removed in (("--delete-during", True),
-                                           ("--delete-delay", False)):
+            for timing, expect_removed in (
+                    ("--delete-during", True),
+                    ("--delete", True),
+                    ("--delete-delay", False),
+                    ("--delete-commit", False),
+                    ("--delete-after", False)):
                 # Re-seed the extra before each run.
                 _write(extra, b"stale extra\n")
                 proxy = _SlicingProxy(server.port, forward_limit=MID_TRANSFER_BYTES, throttle=PROXY_THROTTLE)
@@ -449,12 +475,13 @@ class TestDeleteDelayVsAfterSnapshot:
 
 
 class TestDeleteAfterThreadsKeepSet:
-    """Regression: -m/--threads with the default delete-after timing (plain
-    --delete) must still transmit the keep-set manifest and remove destination
-    extras.  PipelineContextSender.delete_suppressed was left uninitialized, so a
-    garbage true silently skipped the manifest under --threads."""
+    """Regression: -j/--threads must still transmit the delete keep-set in every
+    timing.  PipelineContextSender.delete_suppressed was left uninitialized, so a
+    garbage true silently skipped the late keep-set manifest under --threads.
+    Plain --delete now uses the per-directory plans, while --delete-commit /
+    --delete-after keep exercising the late whole-tree manifest."""
 
-    @pytest.mark.parametrize("delete_flag", ["--delete", "--delete-after"])
+    @pytest.mark.parametrize("delete_flag", ["--delete", "--delete-commit", "--delete-after"])
     def test_threads_delete_after_sends_keep_set(self, delete_flag):
         source, dest, received = _seed_pair("mtkeep")
         extra = os.path.join(received, "d", "old_extra")
@@ -465,7 +492,7 @@ class TestDeleteAfterThreadsKeepSet:
                                    port=server.port)
         assert result.returncode == 0, (result.stderr or result.stdout)[:300]
         assert not os.path.exists(extra), (
-            f"{delete_flag} --threads did not remove an extra: keep-set manifest was suppressed"
+            f"{delete_flag} --threads did not remove an extra: delete keep-set was suppressed"
         )
 
 class TestDeleteDelayMaxDeleteRefilledDir:

tests/integration/test_differential_parity.py

@@ -28,6 +28,7 @@ from common import (  # noqa: E402
     ServerManager,
     TEST_DATA_DIR,
     clean_dir,
+    get_dest_received_dir,
 )
 from parity_caveats import ASPECTS, caveat_for  # noqa: E402
 import parity_harness as H  # noqa: E402
@@ -116,12 +117,32 @@ def seed_delete_excluded(_src, rroot, froot):
         _mk(os.path.join(root, "keep.txt"), b"keep\n", _OLD_MTIME)
 
 
+def seed_filter_protect(_src, rroot, froot):
+    """Destination-only entries, including nested ones, for the receiver-side
+    `protect` rule: the `.log` extras must survive --delete, the rest go."""
+    for root in (rroot, froot):
+        _mk(os.path.join(root, "extra.log"), b"dest-only log\n", _OLD_MTIME)
+        _mk(os.path.join(root, "other.txt"), b"dest-only other\n", _OLD_MTIME)
+        _mk(os.path.join(root, "sub", "extra2.log"), b"nested dest-only log\n", _OLD_MTIME)
+        _mk(os.path.join(root, "sub", "other2.txt"), b"nested dest-only other\n", _OLD_MTIME)
+
+
 def seed_max_delete(_src, rroot, froot):
     for root in (rroot, froot):
         _mk(os.path.join(root, "extra1.txt"), b"e1\n", _OLD_MTIME)
         _mk(os.path.join(root, "extra2.txt"), b"e2\n", _OLD_MTIME)
 
 
+def fuzzy_basis_seed(_src, rroot, froot):
+    """Seed a same-suffix sibling whose name is one edit from the source and
+    whose content matches it, with a DIFFERENT mtime so rsync's exact
+    size+mtime pass cannot fire: both tools must select it via the
+    name-distance pass.  Where the two tools' basis choices coincide the
+    block-level results are identical when the block size is pinned."""
+    for root in (rroot, froot):
+        _mk(os.path.join(root, "report_v1.txt"), H.FUZZY_PAYLOAD, _OLD_MTIME)
+
+
 def max_delete_count_check(_src, rroot, froot, _rs, _fs):
     """The exact survivor set is order-dependent; the count must still match."""
     r = H.snapshot(rroot)
@@ -197,6 +218,18 @@ _CASES = [
     H.Case("chmod", "basic", ["-a", "--chmod=Fu+rwx"], compare_modes=True,
            ci=True, ref="--chmod"),
 
+    # --- delta / similar-file basis (--fuzzy) -----------------------------
+    # Basis choices coincide here (same-suffix sibling, name distance one edit,
+    # content identical); with the block size pinned both tools report the same
+    # Matched/Literal/transferred counters.  The residual (FastSync's narrower
+    # delta size window) is covered by TestFuzzy in test_parity_quickwins.py.
+    H.Case("fuzzy_basis", "fuzzy",
+           ["-a", "--no-whole-file", "--fuzzy", "--stats", "-B8192"],
+           fastsync_flags=["-a", "--incremental", "--delta", "--fuzzy",
+                           "--stats", "--delta-block=8192"],
+           seed=fuzzy_basis_seed, stdout=H.STDOUT_STATS, ci=True,
+           ref="-y/--fuzzy similar-file basis"),
+
     # --- deletion ---------------------------------------------------------
     H.Case("delete", "basic", ["-a", "--delete"], seed=seed_extras,
            server_args=DELETE, ci=True, ref="--delete"),
@@ -208,13 +241,36 @@ _CASES = [
            server_args=DELETE, ref="--delete-delay"),
     H.Case("delete_after", "basic", ["-a", "--delete-after"], seed=seed_extras,
            server_args=DELETE, ref="--delete-after"),
+    H.Case("delete_commit", "basic", ["-a", "--delete-after"], seed=seed_extras,
+           fastsync_flags=["-a", "--delete-commit"], server_args=DELETE,
+           ref="FastSync-only --delete-commit == rsync --delete-after"),
     H.Case("delete_excluded", "filters",
            ["-a", "--delete", "--delete-excluded", "--exclude=*.log"],
            seed=seed_delete_excluded, server_args=DELETE, ref="--delete-excluded"),
+    H.Case("exclude_protect_dest_only", "filters",
+           ["-a", "--delete", "--exclude=*.log"],
+           seed=seed_delete_excluded, server_args=DELETE, ci=True,
+           ref="--delete protects a destination-only excluded entry like rsync"),
     H.Case("max_delete", "basic", ["-a", "--delete", "--max-delete=1"],
            seed=seed_max_delete, server_args=DELETE,
            extra_check=max_delete_count_check, compare_tree=False,
            ref="--max-delete"),
+    H.Case("filter_protect", "filters",
+           ["-a", "--delete", "--filter=P *.log"],
+           seed=seed_filter_protect, server_args=DELETE, ci=True,
+           ref="--filter P/--protect receiver-side delete protection (default during)"),
+    H.Case("filter_protect_during", "filters",
+           ["-a", "--delete-during", "--filter=P *.log"],
+           seed=seed_filter_protect, server_args=DELETE, ci=True,
+           ref="--filter P/--protect under --delete-during"),
+    H.Case("filter_protect_delay", "filters",
+           ["-a", "--delete-delay", "--filter=P *.log"],
+           seed=seed_filter_protect, server_args=DELETE, ci=True,
+           ref="--filter P/--protect under --delete-delay"),
+    H.Case("filter_protect_after", "filters",
+           ["-a", "--delete-after", "--filter=P *.log"],
+           seed=seed_filter_protect, server_args=DELETE, ci=True,
+           ref="--filter P/--protect under the whole-tree --delete-after commit"),
 
     # --- relative / dirs --------------------------------------------------
     H.Case("relative_general", "basic", ["-a", "-R"], layout=H.MIRROR_ABS,
@@ -324,7 +380,11 @@ def _result_aspects(result):
 _STANDALONE_REFS = {
     "incremental_modified": "-i/--itemize-changes + incremental second run",
     "compare_dest": "--compare-dest",
+    "copy_dest": "--copy-dest",
     "link_dest": "--link-dest",
+    "link_dest_stats": "--link-dest + --stats",
+    "verify_basis": "--verify-basis (FastSync-only)",
+    "verify_basis_default": "--verify-basis (default quick-check vs rsync)",
     "added_and_deleted": "--delete across two runs",
     "added_and_deleted_seed": "--delete across two runs",
     "one_file_system": "-x/--one-file-system",
@@ -385,14 +445,17 @@ def test_compare_dest_skips_basis(parity_server_factory):
     fdst = os.path.join(TEST_DATA_DIR, "parity_cmpd_fdst")
     clean_dir(src)
     _mk(os.path.join(src, "f.txt"), b"basis-content\n")
+    _pin(os.path.join(src, "f.txt"), _OLD_MTIME)
     server = parity_server_factory(SUPER)
     rel = os.path.abspath(src).lstrip(os.sep)
 
     # rsync resolves --compare-dest relative to the destination dir; FastSync
     # resolves it under the receive root and appends the mirrored source path.
+    # Both rely on rsync's size+mtime quick-check, so the basis mtime is pinned
+    # to the source's to keep the match deterministic across a second boundary.
     def seed(_src, rroot, froot):
-        _mk(os.path.join(rroot, "basis", "f.txt"), b"basis-content\n")
-        _mk(os.path.join(fdst, "basis", rel, "f.txt"), b"basis-content\n")
+        _mk(os.path.join(rroot, "basis", "f.txt"), b"basis-content\n", _OLD_MTIME)
+        _mk(os.path.join(fdst, "basis", rel, "f.txt"), b"basis-content\n", _OLD_MTIME)
 
     def extra(_src, rroot, froot, _rs, _fs):
         out = []
@@ -420,12 +483,13 @@ def test_link_dest_hardlinks_basis(parity_server_factory):
     fdst = os.path.join(TEST_DATA_DIR, "parity_linkd_fdst")
     clean_dir(src)
     _mk(os.path.join(src, "f.txt"), b"link-basis-content\n")
+    _pin(os.path.join(src, "f.txt"), _OLD_MTIME)
     server = parity_server_factory(SUPER)
     rel = os.path.abspath(src).lstrip(os.sep)
 
     def seed(_src, rroot, froot):
-        _mk(os.path.join(rroot, "basis", "f.txt"), b"link-basis-content\n")
-        _mk(os.path.join(fdst, "basis", rel, "f.txt"), b"link-basis-content\n")
+        _mk(os.path.join(rroot, "basis", "f.txt"), b"link-basis-content\n", _OLD_MTIME)
+        _mk(os.path.join(fdst, "basis", rel, "f.txt"), b"link-basis-content\n", _OLD_MTIME)
 
     def extra(_src, rroot, froot, _rs, _fs):
         r_basis = os.stat(os.path.join(rroot, "basis", "f.txt")).st_ino
@@ -448,6 +512,134 @@ def test_link_dest_hardlinks_basis(parity_server_factory):
     _run_and_check(case_id, result)
 
 
+@requires_rsync
+@parity
+def test_link_dest_stats_matches_rsync(parity_server_factory):
+    """A basis hit must not be counted as created or literal data: rsync reports
+    zero for both, so FastSync's receiver tallies must too (regression for the
+    basis materialization over-report)."""
+    case_id = "link_dest_stats"
+    src = os.path.join(TEST_DATA_DIR, "parity_linkds_src")
+    rdst = os.path.join(TEST_DATA_DIR, "parity_linkds_rdst")
+    fdst = os.path.join(TEST_DATA_DIR, "parity_linkds_fdst")
+    clean_dir(src)
+    _mk(os.path.join(src, "f.txt"), b"link-basis-content\n")
+    _pin(os.path.join(src, "f.txt"), _OLD_MTIME)
+    server = parity_server_factory(SUPER)
+    rel = os.path.abspath(src).lstrip(os.sep)
+
+    def seed(_src, rroot, froot):
+        _mk(os.path.join(rroot, "basis", "f.txt"), b"link-basis-content\n", _OLD_MTIME)
+        _mk(os.path.join(fdst, "basis", rel, "f.txt"), b"link-basis-content\n", _OLD_MTIME)
+
+    result = H.run_differential(
+        src, rdst, fdst,
+        ["-a", "--link-dest=basis", "--stats"],
+        ["-a", f"--link-dest={os.path.join(fdst, 'basis')}", "--incremental", "--stats"],
+        server, seed=seed, ignore_paths=("basis",), stdout=H.STDOUT_STATS)
+    _run_and_check(case_id, result, ref="--link-dest + --stats")
+
+
+@requires_rsync
+@parity
+def test_copy_dest_copies_basis(parity_server_factory):
+    """--copy-dest: a basis match is materialized as an independent copy with the
+    source's attributes, matching rsync (copy then fix attributes)."""
+    case_id = "copy_dest"
+    src = os.path.join(TEST_DATA_DIR, "parity_copyd_src")
+    rdst = os.path.join(TEST_DATA_DIR, "parity_copyd_rdst")
+    fdst = os.path.join(TEST_DATA_DIR, "parity_copyd_fdst")
+    clean_dir(src)
+    _mk(os.path.join(src, "f.txt"), b"copy-basis-content\n")
+    _pin(os.path.join(src, "f.txt"), 1_600_000_000)
+    os.chmod(os.path.join(src, "f.txt"), 0o755)
+    server = parity_server_factory(SUPER)
+    rel = os.path.abspath(src).lstrip(os.sep)
+
+    def seed(_src, rroot, froot):
+        # Basis content matches the source; give the basis a different mode so a
+        # wrong "keep basis attributes" implementation is visible.
+        _mk(os.path.join(rroot, "basis", "f.txt"), b"copy-basis-content\n",
+            1_600_000_000)
+        os.chmod(os.path.join(rroot, "basis", "f.txt"), 0o644)
+        _mk(os.path.join(fdst, "basis", rel, "f.txt"), b"copy-basis-content\n",
+            1_600_000_000)
+        os.chmod(os.path.join(fdst, "basis", rel, "f.txt"), 0o644)
+
+    def extra(_src, rroot, froot, _rs, _fs):
+        out = []
+        bases = {"rsync": os.path.join(rroot, "basis", "f.txt"),
+                 "fastsync": os.path.join(fdst, "basis", rel, "f.txt")}
+        for label, root in (("rsync", rroot), ("fastsync", froot)):
+            target = os.path.join(root, "f.txt")
+            if not os.path.exists(target):
+                out.append(f"{label}: f.txt missing")
+                continue
+            if os.stat(target).st_ino == os.stat(bases[label]).st_ino:
+                out.append(f"{label}: f.txt is hard-linked, not copied")
+            if (os.stat(target).st_mode & 0o777) != 0o755:
+                out.append(f"{label}: f.txt mode "
+                           f"{oct(os.stat(target).st_mode & 0o777)} != 0o755")
+        return out
+
+    result = H.run_differential(
+        src, rdst, fdst,
+        ["-a", "--copy-dest=basis"],
+        ["-a", f"--copy-dest={os.path.join(fdst, 'basis')}", "--incremental"],
+        server, seed=seed, ignore_paths=("basis",), extra_check=extra,
+        compare_modes=True)
+    _run_and_check(case_id, result)
+
+
+@requires_rsync
+@parity
+def test_verify_basis_restores_strict_content(parity_server_factory):
+    """Default matches rsync's metadata quick-check; FastSync-only
+    `--verify-basis` restores strict content equality and transfers the source
+    when a same-size/different-content basis would otherwise be trusted."""
+    case_id = "verify_basis"
+    src = os.path.join(TEST_DATA_DIR, "parity_vbasis_src")
+    rdst = os.path.join(TEST_DATA_DIR, "parity_vbasis_rdst")
+    fdst = os.path.join(TEST_DATA_DIR, "parity_vbasis_fdst")
+    clean_dir(src)
+    _mk(os.path.join(src, "f.txt"), b"AAAA\n")
+    _pin(os.path.join(src, "f.txt"), _OLD_MTIME)
+    server = parity_server_factory(SUPER)
+    rel = os.path.abspath(src).lstrip(os.sep)
+
+    def seed(_src, rroot, froot):
+        # Same size and mtime as the source, different bytes: a metadata
+        # quick-check trusts it; --verify-basis must not.
+        for root, basis_rel in ((rroot, os.path.join("basis", "f.txt")),
+                                (fdst, os.path.join("basis", rel, "f.txt"))):
+            _mk(os.path.join(root, basis_rel), b"BBBB\n", _OLD_MTIME)
+
+    # Default: both tools trust the basis (rsync's quick check), so the
+    # destination carries the basis bytes and the trees match.
+    result = H.run_differential(
+        src, rdst, fdst,
+        ["-a", "--link-dest=basis"],
+        ["-a", f"--link-dest={os.path.join(fdst, 'basis')}", "--incremental"],
+        server, seed=seed, ignore_paths=("basis",))
+    _run_and_check(case_id + "_default", result)
+
+    # --verify-basis (FastSync only): the digest mismatch rejects the basis and
+    # the source is transferred, so the destination is the source bytes.  rsync
+    # has no such flag; assert the FastSync outcome directly against the source.
+    fdst2 = os.path.join(TEST_DATA_DIR, "parity_vbasis_fdst2")
+    clean_dir(fdst2)
+    for root, basis_rel in ((fdst2, os.path.join("basis", rel, "f.txt")),):
+        _mk(os.path.join(root, basis_rel), b"BBBB\n", _OLD_MTIME)
+    result, _ = H.run_fastsync(src, fdst2,
+                               ["-a", f"--link-dest={os.path.join(fdst2, 'basis')}",
+                                "--incremental", "--verify-basis"], server.port)
+    assert result.returncode == 0, (result.stderr or result.stdout)[:300]
+    target = os.path.join(get_dest_received_dir(fdst2, src), "f.txt")
+    with open(target, "rb") as fh:
+        assert fh.read() == b"AAAA\n", \
+            "--verify-basis must reject the same-size/different-content basis"
+
+
 @requires_rsync
 @parity
 def test_added_and_deleted_between_runs(parity_server_factory):

tests/integration/test_features.py

@@ -589,11 +589,10 @@ class TestRemoteDryRun:
 
         Covers the three cases that a real run protects: the file being updated
         (in the keep set), a filter-excluded source entry (protected prefix), and
-        a --max-size-pruned source entry (always-protected prefix).  Only the
-        genuine destination-only extras may appear.  Residual: a destination-only
-        entry matching an exclude pattern is still removed (FastSync derives
-        delete protection from the source scan, not a receiver filter engine);
-        that divergence is pinned by TestOptionParity.
+        a --max-size-pruned source entry (always-protected prefix).  Track 4a
+        adds a fourth: a destination-only entry matching the exclude rule is
+        re-derived on the receiver and also protected, so only the genuine
+        destination-only `extra.txt` appears.
         """
         source = os.path.join(TEST_DATA_DIR, "dryrep_src")
         rdst = os.path.join(TEST_DATA_DIR, "dryrep_rdst")
@@ -610,7 +609,8 @@ class TestRemoteDryRun:
         os.makedirs(received, exist_ok=True)
         for root in (rdst, received):
             for name, data in (("a.txt", b"old\n"), ("keep.log", b"log\n"),
-                               ("big.bin", b"B" * 2000), ("extra.txt", b"extra\n")):
+                               ("big.bin", b"B" * 2000), ("extra.txt", b"extra\n"),
+                               ("stray.log", b"dest only\n")):
                 with open(os.path.join(root, name), "wb") as fh:
                     fh.write(data)
                 os.utime(os.path.join(root, name), (1_500_000_000, 1_500_000_000))
@@ -631,6 +631,8 @@ class TestRemoteDryRun:
         fs_del = sorted(l for l in (result.stdout or "").splitlines()
                         if l.startswith("*deleting"))
         assert fs_del == rsync_del, f"rsync={rsync_del}\nfastsync={fs_del}"
+        assert os.path.exists(os.path.join(received, "stray.log")), \
+            "destination-only exclude match must be protected in the dry-run report"
 
     @pytest.mark.ci
     def test_remote_dry_run_quiet_is_silent(self, shared_server):
@@ -3980,15 +3982,16 @@ class TestDeleteTiming:
             assert _read_file(os.path.join(received, "sub", "deep.txt")) == b"deeply nested file\n", \
                 f"{flag}: nested file was not written after the early deletion"
 
-    @pytest.mark.parametrize("flag", ["--delete", "--delete-after"])
+    @pytest.mark.parametrize("flag", ["--delete-commit", "--delete-after"])
     @pytest.mark.parametrize("mt", [False, True])
     def test_late_flags_commit_only_after_success(self, flag, mt):
-        """Plain --delete/--delete-after defer deletion until the whole transfer
+        """--delete-commit/--delete-after defer deletion until the whole transfer
         succeeds: a mid-transfer write failure must leave every extra in place
-        (commit-style safety).  The -m receiver must also keep the extras: the
-        deferred keep-set is committed by the server only after the disk-writer
-        thread has finished, and a failing writer means the manifest is freed,
-        never applied."""
+        (commit-style safety).  Plain --delete no longer defers (it defaults to
+        delete-during), so only the explicitly late timings are exercised here.
+        The --threads receiver must also keep the extras: the deferred keep-set is
+        committed by the server only after the disk-writer thread has finished,
+        and a failing writer means the manifest is freed, never applied."""
         source = self._seed("late")
         dest = os.path.join(TEST_DATA_DIR, "deltiming_late_dst")
         clean_dir(dest)
@@ -4693,11 +4696,11 @@ class TestDeletePolicy:
             finally:
                 os.chmod(source, 0o755)
 
-    def test_delete_excluded_protection_is_sender_derived(self):
+    def test_delete_protection_reapplied_on_receiver(self):
         """Plain --delete protects destination mirrors of files the SOURCE scan
-        excluded, but a destination-only file that merely matches an exclude
-        rule is still an extra and is removed (protection never re-applies rules
-        to the destination)."""
+        excluded, and (track 4a) also protects a destination-only file matching
+        an exclude rule because the compiled rule set is re-applied on the
+        receiver, matching rsync."""
         source = os.path.join(TEST_DATA_DIR, "senderderived_src")
         clean_dir(source)
         self._write(os.path.join(source, "keep.txt"), b"kept\n")
@@ -4717,8 +4720,8 @@ class TestDeletePolicy:
                 f"delete sync failed: {(result.stderr or result.stdout)[:300]}"
             assert os.path.exists(os.path.join(received, "secret.log")), \
                 "source-excluded mirror was deleted under plain --delete"
-            assert not os.path.exists(os.path.join(received, "stray.log")), \
-                "destination-only file matching the exclude rule was left (should be deleted)"
+            assert os.path.exists(os.path.join(received, "stray.log")), \
+                "destination-only file matching the exclude rule must be protected like rsync"
 
 
 def _pin_mtime(path, ts):
@@ -4738,11 +4741,12 @@ class TestBasisDestDirs:
     STAGING = ".fastsync-stage"
     TS = 1577836800  # 2020-01-01 00:00:00 UTC, used to pin matching mtimes
 
-    # fixture files: source and basis share the mtime pin, so a basis "match"
-    # is decided purely by content (xxHash).  unchanged.txt is byte-identical;
-    # changed.txt is byte-DIFFERENT but has the SAME SIZE as the source (and
-    # the same pinned mtime), which is what forces the content-hash gate;
-    # added.txt does not exist in the basis at all.
+    # fixture files: source and basis share the mtime pin, so the DEFAULT
+    # (rsync-parity) quick-check is a size+mtime match and trusts the basis even
+    # when the body differs.  unchanged.txt is byte-identical; changed.txt is
+    # byte-DIFFERENT but has the SAME SIZE as the source (and the same pinned
+    # mtime), which is what the FastSync-only --verify-basis content gate
+    # rejects; added.txt does not exist in the basis at all.
     UNCHANGED = "unchanged.txt"
     CHANGED = "changed.txt"
     ADDED = "added.txt"
@@ -4782,18 +4786,19 @@ class TestBasisDestDirs:
         }
 
     def _basis_tree(self, prefix):
-        # unchanged.txt is identical to the source; changed.txt has the SAME
-        # byte size and pinned mtime but a different body (equal size forces
-        # the xxHash gate); added.txt is missing from the basis.
+        # unchanged.txt is identical to the source; changed.txt has a DIFFERENT
+        # size (and body) so the size leg of the quick-check fails and it is
+        # transferred normally; added.txt is missing from the basis.
         return {
             self.UNCHANGED: b"stable content v1\n",
-            self.CHANGED: b"CHANGED CONTENT NOW\n",
+            self.CHANGED: b"CHANGED CONTENT NOW AND LONGER\n",
         }
 
-    def test_same_size_different_content_is_not_a_basis_match(self, shared_server):
-        # Core safety property: equal size + pinned mtime but different content
-        # must NEVER be hard-linked or copied from the basis -- the xxHash gate
-        # rejects it and the sender's data is transferred instead.
+    def test_same_size_different_content_default_trusts_quick_check(self, shared_server):
+        # Default rsync-parity behavior: equal size + pinned mtime is a basis
+        # match, so the basis body is materialized/linked without reading it.
+        # This mirrors rsync 3.4.1's quick check (differential-tested in
+        # test_differential_parity.py::test_verify_basis_restores_strict_content).
         for flag, basis_dir in (("--link-dest", "szlb"), ("--copy-dest", "szcp"),
                                 ("--compare-dest", "szcmp")):
             source = self._make_source("basis_same_size_src",
@@ -4805,7 +4810,36 @@ class TestBasisDestDirs:
             result, _ = run_client(source, dest, flags=[f"{flag}={basis_dir}"],
                                    port=shared_server.port)
             assert result.returncode == 0, \
-                f"{flag} same-size mismatch failed: {result.stderr[:300]}"
+                f"{flag} same-size quick-check failed: {result.stderr[:300]}"
+            received = get_dest_received_dir(dest, source)
+            dest_file = os.path.join(received, self.UNCHANGED)
+            if flag == "--compare-dest":
+                assert not os.path.exists(dest_file), \
+                    f"{flag}: compare-dest must leave a matching file sparse"
+            else:
+                assert _read_file(dest_file) == b"SAME LENGTH BODY!", \
+                    f"{flag}: default quick-check did not trust the basis body"
+                if flag == "--link-dest":
+                    assert os.stat(dest_file).st_ino == os.stat(basis_file).st_ino, \
+                        f"{flag}: basis was not hard-linked"
+
+    def test_verify_basis_rejects_same_size_different_content(self, shared_server):
+        # FastSync-only --verify-basis: the whole-file digest gate rejects the
+        # same-size/different-content basis, so the source data is transferred
+        # instead of the wrong basis bytes.
+        for flag, basis_dir in (("--link-dest", "vszlb"), ("--copy-dest", "vszcp"),
+                                ("--compare-dest", "vszcmp")):
+            source = self._make_source("basis_verify_src",
+                                       {self.UNCHANGED: b"same length body\n"})
+            dest = os.path.join(TEST_DATA_DIR, f"basis_verify_dst_{basis_dir}")
+            clean_dir(dest)
+            basis_file = self._seed_basis_file(dest, source, basis_dir, self.UNCHANGED,
+                                               b"SAME LENGTH BODY!")
+            result, _ = run_client(source, dest,
+                                   flags=[f"{flag}={basis_dir}", "--verify-basis"],
+                                   port=shared_server.port)
+            assert result.returncode == 0, \
+                f"{flag} --verify-basis failed: {result.stderr[:300]}"
             received = get_dest_received_dir(dest, source)
             dest_file = os.path.join(received, self.UNCHANGED)
             assert _read_file(dest_file) == b"same length body\n", \
@@ -4837,11 +4871,13 @@ class TestBasisDestDirs:
             self._source_tree("c")[self.ADDED], "added file not transferred"
 
     @pytest.mark.ci
-    def test_dry_run_compare_dest_does_not_read_basis(self, shared_server):
-        # A dry-run --compare-dest must never read/hash the basis file: doing so
-        # is a 1-bit content oracle against the client-supplied digest.  Even a
-        # byte-identical basis with a matching size+mtime is therefore reported
-        # as would-transfer, and nothing is created.
+    def test_dry_run_compare_dest_quick_check_does_not_read_basis(self, shared_server):
+        # A dry-run --compare-dest must never read/hash the basis file.  Under
+        # the default metadata quick-check a matching basis is reported as a
+        # skip (matching rsync) without reading it; nothing is created.  Under
+        # --verify-basis, which would require hashing, the dry-run cannot
+        # confirm the hit (that would be a 1-bit content oracle) and reports
+        # would-transfer instead.
         source = self._make_source("basis_dry_src", {self.UNCHANGED: b"stable content v1\n"})
         dest = os.path.join(TEST_DATA_DIR, "basis_dry_dst")
         clean_dir(dest)
@@ -4852,11 +4888,30 @@ class TestBasisDestDirs:
                                port=shared_server.port)
         assert result.returncode == 0, \
             f"dry-run compare-dest failed: {result.stderr[:300]}"
-        assert self.UNCHANGED in result.stdout, (
-            "dry-run compare-dest silently skipped: receiver read the basis content"
+        assert self.UNCHANGED not in result.stdout, (
+            "dry-run compare-dest did not honor the metadata quick-check "
+            "(reported would-transfer for a matching basis)"
         )
         assert _snapshot_tree(dest) == before, "dry-run compare-dest mutated the destination"
 
+        # --verify-basis: the hit needs the basis content, which a dry-run must
+        # not read, so the file is reported as would-transfer.
+        dest2 = os.path.join(TEST_DATA_DIR, "basis_dry_verify_dst")
+        clean_dir(dest2)
+        self._seed_basis(dest2, source, "drybasis", {self.UNCHANGED: b"stable content v1\n"})
+        before2 = _snapshot_tree(dest2)
+        result, _ = run_client(source, dest2,
+                               flags=["--compare-dest=drybasis", "--dry-run",
+                                      "--verify-basis"],
+                               port=shared_server.port)
+        assert result.returncode == 0, \
+            f"dry-run --verify-basis compare-dest failed: {result.stderr[:300]}"
+        assert self.UNCHANGED in result.stdout, (
+            "dry-run --verify-basis must not read the basis to confirm a hit"
+        )
+        assert _snapshot_tree(dest2) == before2, \
+            "dry-run --verify-basis compare-dest mutated the destination"
+
     def test_compare_dest_content_mismatch_forces_transfer(self, shared_server):
         # The basis holds a file with a DIFFERENT body: even though it shares
         # the mtime pin, the xxHash check fails and the data must be sent.
@@ -5095,27 +5150,36 @@ class TestBasisDestDirs:
         assert os.stat(dest_file).st_ino != os.stat(basis_file).st_ino, \
             "--ignore-times must not hard-link to a basis file"
 
-    def test_basis_refuses_file_above_whole_file_limit(self, shared_server):
-        # Every whole-file payload path in FastSync (basis dirs included) is
-        # bounded by MAX_RECEIVE_WHOLE_FILE_SIZE.  rsync supports basis dirs for
-        # arbitrary sizes; FastSync refuses such a run up front with a clear
-        # diagnostic instead of letting the receiver abort the whole transfer
-        # mid-stream with no client-side explanation.
+    def test_basis_handles_file_above_whole_file_limit(self, shared_server):
+        # Track 5a: a basis hit streams the copy (and the --verify-basis digest
+        # streams the basis), so a source larger than the whole-file payload
+        # bound is supported for basis dirs exactly like rsync.  A basis MISS
+        # still falls back to the normal transfer, which keeps its own bound.
         source = self._make_source("basis_oversize_src", {"small.txt": b"ok\n"})
         big = os.path.join(source, "huge.bin")
         with open(big, "wb") as fh:
             os.ftruncate(fh.fileno(), 256 * 1024 * 1024 + 4096)
         dest = os.path.join(TEST_DATA_DIR, "basis_oversize_dst")
         clean_dir(dest)
-        result, _ = run_client(source, dest, flags=["--link-dest=nope"],
-                               port=shared_server.port)
-        assert result.returncode != 0, \
-            "basis run with an over-limit file unexpectedly succeeded"
-        assert "larger than" in result.stderr, \
-            f"no clear over-limit diagnostic: {result.stderr[:300]}"
         received = get_dest_received_dir(dest, source)
-        assert not os.path.exists(received), \
-            "over-limit basis run transferred files before failing"
+        rel = os.path.relpath(received, dest)
+        basis_big = os.path.join(dest, "ob", rel, "huge.bin")
+        os.makedirs(os.path.dirname(basis_big), exist_ok=True)
+        shutil.copyfile(big, basis_big)
+        os.utime(basis_big, (self.TS, self.TS))
+        os.utime(big, (self.TS, self.TS))
+
+        result, _ = run_client(source, dest,
+                               flags=["--link-dest=ob", "--incremental"],
+                               port=shared_server.port)
+        assert result.returncode == 0, \
+            f"over-limit basis run failed: {result.stderr[:300]}"
+        dest_big = os.path.join(received, "huge.bin")
+        assert os.path.exists(dest_big), "over-limit basis hit was not materialized"
+        assert os.path.getsize(dest_big) == 256 * 1024 * 1024 + 4096
+        assert os.stat(dest_big).st_ino == os.stat(basis_big).st_ino, \
+            "over-limit --link-dest did not hard-link to the basis"
+        assert _read_file(os.path.join(received, "small.txt")) == b"ok\n"
 
 
 def _random_payloads(size=2 * 1024 * 1024, changed=64 * 1024, seed=1234):

tests/integration/test_option_parity.py

@@ -478,14 +478,14 @@ class TestRemoteOptionDaemon:
         assert "remote-option" in (result.stderr + result.stdout)
 
 
-class TestFilterProtectDivergence:
-    """Documented residual: a protect rule that matches only a destination-only
-    entry is not re-derived on the receiver (FastSync derives delete protection
-    from the source scan), so rsync protects the extra but FastSync removes it."""
+class TestFilterProtect:
+    """Receiver-derived delete protection: a `protect`/`P` rule is compiled by
+    the sender and sent on the config frame, so the receiver shields a
+    destination-only entry that never appeared on the sender, matching rsync."""
 
     @requires_rsync
     @pytest.mark.ci
-    def test_protect_dest_only_divergence(self, shared_server):
+    def test_protect_dest_only_matches_rsync(self, shared_server):
         source = os.path.join(TEST_DATA_DIR, "fpd_src")
         dest = os.path.join(TEST_DATA_DIR, "fpd_dst")
         rdst = os.path.join(TEST_DATA_DIR, "fpd_rdst")
@@ -498,6 +498,7 @@ class TestFilterProtectDivergence:
         rsync_result = _rsync(["-a", "--delete", "--filter=P *.log", source + "/", rdst + "/"])
         assert rsync_result.returncode == 0, rsync_result.stderr
         assert os.path.exists(os.path.join(rdst, "extra.log")), "rsync did not protect extra.log"
+        assert not os.path.exists(os.path.join(rdst, "other.txt")), "rsync did not delete other.txt"
 
         clean_dir(dest)
         received = get_dest_received_dir(dest, source)
@@ -509,9 +510,29 @@ class TestFilterProtectDivergence:
                                    flags=["-a", "--delete", "--filter=P *.log"],
                                    port=server.port)
         assert result.returncode == 0, (result.stderr or result.stdout)[:200]
-        # Pin the known divergence: FastSync deletes the destination-only file.
-        assert not os.path.exists(os.path.join(received, "extra.log")), (
-            "FastSync now protects destination-only P matches; the --filter row may be "
-            "upgradable to full parity"
-        )
+        assert os.path.exists(os.path.join(received, "extra.log")), (
+            "FastSync must protect a destination-only P match like rsync")
         assert not os.path.exists(os.path.join(received, "other.txt"))
+
+    @pytest.mark.ci
+    def test_protect_dest_only_dry_run_enumeration(self, shared_server):
+        source = os.path.join(TEST_DATA_DIR, "fpd_nd_src")
+        dest = os.path.join(TEST_DATA_DIR, "fpd_nd_dst")
+        clean_dir(source)
+        _write(os.path.join(source, "keep.txt"), b"keep\n")
+        received = get_dest_received_dir(dest, source)
+        clean_dir(received)
+        _write(os.path.join(received, "keep.txt"), b"keep\n")
+        _write(os.path.join(received, "extra.log"), b"extra\n")
+        _write(os.path.join(received, "other.txt"), b"other\n")
+        with ServerManager() as server:
+            server.start(extra_args=["--allow-delete"])
+            result, _ = run_client(source, dest,
+                                   flags=["-a", "-n", "--delete", "--out-format=%n",
+                                          "--filter=P *.log"],
+                                   port=server.port)
+        assert result.returncode == 0, (result.stderr or result.stdout)[:300]
+        assert "other.txt" in result.stdout, result.stdout
+        assert "extra.log" not in result.stdout, result.stdout
+        assert os.path.exists(os.path.join(received, "extra.log"))
+        assert os.path.exists(os.path.join(received, "other.txt"))

tests/integration/test_parity_quickwins.py

@@ -719,13 +719,18 @@ class TestVerifyAndFlip:
         source = self._src("cmpd")
         dest = self._dst("cmpd")
         rdst = self._dst("cmpd_r")
+        # Pin the mtime so rsync's size+mtime quick-check (and FastSync's
+        # default) matches deterministically across a second boundary.
+        OLD = 1_500_000_000
         with open(os.path.join(source, "f.txt"), "wb") as fh:
             fh.write(b"basis-content\n")
+        os.utime(os.path.join(source, "f.txt"), (OLD, OLD))
         # rsync resolves --compare-dest relative to the destination dir; its
         # basis file sits at the transfer-relative path.
         os.makedirs(os.path.join(rdst, "basis"), exist_ok=True)
         with open(os.path.join(rdst, "basis", "f.txt"), "wb") as fh:
             fh.write(b"basis-content\n")
+        os.utime(os.path.join(rdst, "basis", "f.txt"), (OLD, OLD))
         rs = _rsync(["-a", "--compare-dest=basis", source + "/", rdst + "/"])
         assert rs.returncode == 0, rs.stderr
         assert not os.path.exists(os.path.join(rdst, "f.txt")), \
@@ -738,6 +743,7 @@ class TestVerifyAndFlip:
         os.makedirs(basis, exist_ok=True)
         with open(os.path.join(basis, "f.txt"), "wb") as fh:
             fh.write(b"basis-content\n")
+        os.utime(os.path.join(basis, "f.txt"), (OLD, OLD))
         received = get_dest_received_dir(dest, source)
         result, _ = run_client(source, dest,
                                flags=["--compare-dest=basis", "--incremental"],
@@ -751,14 +757,17 @@ class TestVerifyAndFlip:
     def test_link_dest_hardlinks_matches_rsync(self, shared_server):
         source = self._src("linkd")
         dest = self._dst("linkd")
+        OLD = 1_500_000_000
         with open(os.path.join(source, "f.txt"), "wb") as fh:
             fh.write(b"link-basis-content\n")
+        os.utime(os.path.join(source, "f.txt"), (OLD, OLD))
         rel = os.path.abspath(source).lstrip(os.sep)
         basis = os.path.join(dest, "basis", rel)
         os.makedirs(basis, exist_ok=True)
         basis_file = os.path.join(basis, "f.txt")
         with open(basis_file, "wb") as fh:
             fh.write(b"link-basis-content\n")
+        os.utime(basis_file, (OLD, OLD))
         received = get_dest_received_dir(dest, source)
         result, _ = run_client(source, dest,
                                flags=["--link-dest=basis", "--incremental"],
@@ -771,12 +780,11 @@ class TestVerifyAndFlip:
 
     @requires_rsync
     def test_basis_dir_size_only_content_residual(self, shared_server):
-        """Documented residual (RSYNC_COMPAT.md basis-dir rows): FastSync
-        xxHash-verifies a basis hit, while rsync's `--size-only` quick check
-        trusts the size alone.  With a same-size, different-content basis,
-        rsync links/copies the wrong basis content while FastSync transfers the
-        source.  This test pins both observed behaviors (FastSync is stricter,
-        so the rows are reclassified Divergent)."""
+        """rsync parity (default): a basis hit is decided by the metadata
+        quick-check alone.  With `--size-only`, a same-size, different-content
+        basis is trusted, so rsync links the basis content and FastSync must now
+        do the same instead of xxHash-verifying it.  `--verify-basis` restores
+        the stricter content equality (covered by the differential test)."""
         source = self._src("basissz")
         rdest = self._dst("basissz_r")
         fdest = self._dst("basissz_f")
@@ -806,9 +814,123 @@ class TestVerifyAndFlip:
                                flags=["-a", "--size-only", "--link-dest=basis", "--incremental"],
                                port=shared_server.port)
         assert result.returncode == 0, result.stderr[:300]
+        with open(os.path.join(received, "f.txt"), "rb") as fh:
+            assert fh.read() == b"BBBB\n", \
+                "FastSync must trust the metadata quick-check exactly like rsync"
+
+    @requires_rsync
+    def test_verify_basis_restores_content_check(self, shared_server):
+        """FastSync-only `--verify-basis`: a same-size, same-mtime basis with
+        different content is rejected by the whole-file digest, so the source is
+        transferred instead of installing the wrong basis bytes.  The default
+        (no flag) installs the basis content, matching rsync."""
+        source = self._src("vbasis")
+        fdest = self._dst("vbasis_f")
+        with open(os.path.join(source, "f.txt"), "wb") as fh:
+            fh.write(b"AAAA\n")
+        OLD = 1_400_000_000
+        os.utime(os.path.join(source, "f.txt"), (OLD, OLD))
+        rel = os.path.abspath(source).lstrip(os.sep)
+        basis = os.path.join(fdest, "basis", rel)
+        os.makedirs(basis, exist_ok=True)
+        with open(os.path.join(basis, "f.txt"), "wb") as fh:
+            fh.write(b"BBBB\n")
+        os.utime(os.path.join(basis, "f.txt"), (OLD, OLD))
+        received = get_dest_received_dir(fdest, source)
+        result, _ = run_client(source, fdest,
+                               flags=["-a", "--link-dest=basis", "--incremental",
+                                      "--verify-basis"],
+                               port=shared_server.port)
+        assert result.returncode == 0, result.stderr[:300]
         with open(os.path.join(received, "f.txt"), "rb") as fh:
             assert fh.read() == b"AAAA\n", \
-                "FastSync must verify the basis content and transfer the source"
+                "--verify-basis must reject the same-size/different-content basis"
+
+
+def _stat_bytes(output, key):
+    """Parse a --stats byte counter (e.g. ``Matched data: 65,536 bytes``)."""
+    for line in output.splitlines():
+        if line.startswith(key + ":"):
+            raw = line.split(":", 1)[1].strip().split()[0]
+            return int(raw.replace(",", ""))
+    return None
+
+
+class TestFuzzy:
+    """Track 5b: `-y`/`--fuzzy` is an internal bandwidth optimization with a
+    byte-exact result.  FastSync ports rsync 3.4.1's weighted-Levenshtein name
+    heuristic, so where both delta engines admit the candidate the tools pick
+    the same basis (the ``fuzzy_basis`` differential asserts the tree and the
+    Matched/Literal counters match with the block size pinned).  The residual is
+    candidate ELIGIBILITY: FastSync's delta size gate (both files >= 16 KiB and
+    a <= 10x size ratio) is narrower than rsync's, which empirically uses a
+    fuzzy basis well beyond 10x and below 16 KiB.  These tests pin the window
+    boundary and prove the byte-exact fallback on both sides of it."""
+
+    _BASE = b"the quick brown fox jumps over the lazy dog\n" * 4000
+
+    def _src(self, tag):
+        source = os.path.join(TEST_DATA_DIR, f"fz_{tag}_src")
+        clean_dir(source)
+        return source
+
+    def _dst(self, tag):
+        d = os.path.join(TEST_DATA_DIR, f"fz_{tag}_dst")
+        clean_dir(d)
+        return d
+
+    def _run_both(self, shared_server, source, dest, rdst, payload, sibling,
+                  rs_extra=(), fs_extra=()):
+        with open(os.path.join(source, "report_v2.txt"), "wb") as fh:
+            fh.write(payload)
+        for root in (rdst, get_dest_received_dir(dest, source)):
+            os.makedirs(root, exist_ok=True)
+            with open(os.path.join(root, "report_v1.txt"), "wb") as fh:
+                fh.write(sibling)
+        rs = _rsync(["-a", "--no-whole-file", "--fuzzy", "--stats"] +
+                    list(rs_extra) + [source + "/", rdst + "/"])
+        assert rs.returncode == 0, rs.stderr[:300]
+        result, _ = run_client(
+            source, dest,
+            flags=["-a", "--incremental", "--delta", "--fuzzy", "--stats"] +
+            list(fs_extra),
+            port=shared_server.port)
+        assert result.returncode == 0, result.stderr[:300]
+        _assert_same_tree(rdst, get_dest_received_dir(dest, source), "(--fuzzy)")
+        return rs, result
+
+    @requires_rsync
+    def test_fuzzy_above_size_window_declines_but_tree_exact(self, shared_server):
+        """A sibling >10x the source is used by rsync but declined by FastSync's
+        delta size-ratio gate; both destinations stay byte-identical."""
+        n = 65536
+        payload = (self._BASE * ((n // len(self._BASE)) + 1))[:n]
+        sibling = (self._BASE * 200)[: n * 20]
+        source, dest, rdst = (self._src("big"), self._dst("big"),
+                              self._dst("big_r"))
+        rs, result = self._run_both(shared_server, source, dest, rdst,
+                                    payload, sibling)
+        assert _stat_bytes(rs.stdout, "Matched data") > 0, \
+            "rsync should still use a >10x fuzzy basis"
+        assert _stat_bytes(result.stdout, "Matched data") == 0, \
+            "FastSync's 10x delta size-ratio gate must decline the oversized basis"
+        assert _stat_bytes(result.stdout, "Literal data") == n
+
+    @requires_rsync
+    def test_fuzzy_below_delta_minimum_declines_but_tree_exact(self, shared_server):
+        """A sibling below the 16 KiB delta minimum is used by rsync but never
+        enters FastSync's delta/fuzzy path; both trees stay byte-identical."""
+        n = 8192
+        payload = (self._BASE * ((n // len(self._BASE)) + 1))[:n]
+        source, dest, rdst = (self._src("small"), self._dst("small"),
+                              self._dst("small_r"))
+        rs, result = self._run_both(shared_server, source, dest, rdst,
+                                    payload, payload)
+        assert _stat_bytes(rs.stdout, "Matched data") > 0, \
+            "rsync applies --fuzzy below 16 KiB"
+        assert _stat_bytes(result.stdout, "Matched data") == 0, \
+            "FastSync's 16 KiB delta minimum must bypass the fuzzy basis"
+        assert _stat_bytes(result.stdout, "Literal data") == n
 
 
 class TestIgnoreExistingShortCircuit:

tests/integration/test_preflight.py

@@ -118,8 +118,8 @@ class TestProtocol:
         shutil.rmtree(dest, ignore_errors=True)
         os.makedirs(dest)
         _seed_protocol_source(source)
-        for bad in ("2.22.0", "2.21.0", "2.20.0", "2.19.0", "2.18.0", "2.17.0", "2.15.0", "2.16.0",
-                    "216", "31"):
+        for bad in ("2.27.0", "2.26.0", "2.25.0", "2.24.0", "2.23.0", "2.22.0", "2.21.0", "2.20.0",
+                    "2.19.0", "2.18.0", "2.17.0", "2.15.0", "2.16.0", "216", "31"):
             result, _ = run_client(source, dest, flags=[f"--protocol={bad}"],
                                    port=shared_server.port)
             assert result.returncode != 0, f"--protocol={bad} should be rejected"

tests/test_client_cli.c

@@ -340,6 +340,7 @@ static void test_parse_args_protocol_accept_current() {
 static void test_parse_args_protocol_rejects_other_versions() {
   static const char* const bad_versions[] = {"2.17",   "2.16",   "2.15.0", "2.16.0", "2.17.0",
                                              "2.18.0", "2.19.0", "2.20.0", "2.21.0", "2.22.0",
+                                             "2.23.0", "2.24.0", "2.25.0", "2.26.0", "2.27.0",
                                              "216",    "31",     "abc",    ""};
   for (size_t i = 0; i < sizeof(bad_versions) / sizeof(bad_versions[0]); i++) {
     Config* cfg = valid_client_config();
@@ -1045,6 +1046,23 @@ static void test_parse_args_basis_dirs() {
   config_delete(cfg);
 }
 
+/* --verify-basis (FastSync-only, long-only): default off; parses on as a plain
+   boolean and leaves the basis implications intact. */
+static void test_parse_args_verify_basis() {
+  Config* cfg = config_create();
+  EXPECT_FALSE(cfg->verify_basis);
+  config_delete(cfg);
+
+  cfg = config_create();
+  int positional_args[2];
+  int positional_count = 0;
+  char* argv[] = {"fastsync", "--link-dest=prior", "--verify-basis", "/src", "/dst"};
+  EXPECT_EQ_INT(parse_args(cfg, 5, argv, positional_args, &positional_count), 0);
+  EXPECT_TRUE(cfg->verify_basis);
+  EXPECT_TRUE(config_has_basis(cfg));
+  config_delete(cfg);
+}
+
 /* Escaping or degenerate basis-dir values must be rejected up front (they would
    resolve outside the destination root on the receiver); an absolute path is
    accepted (rsync parity) and canonicalized with its leading '/' preserved. */
@@ -1132,6 +1150,63 @@ static void test_parse_args_delete_timing_flags() {
   config_delete(cfg);
 }
 
+/* Plain --delete with no explicit timing defaults to delete-during, matching
+ * rsync's --del default (progressive deletion).  --delete-commit is the
+ * FastSync-only long spelling that selects rsync's --delete-after timing (the
+ * late whole-tree commit), and an explicit timing always wins over the default.
+ */
+static void test_parse_args_delete_default_timing_and_commit() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--delete", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+  EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), 0);
+  EXPECT_TRUE(cfg->use_delete);
+  EXPECT_TRUE(cfg->delete_during);
+  EXPECT_FALSE(cfg->delete_before);
+  EXPECT_FALSE(cfg->delete_delay);
+  EXPECT_FALSE(cfg->delete_after);
+  cfg->send_directory = str_dup("/src");
+  cfg->receive_root_directory = str_dup("/dst");
+  EXPECT_TRUE(validate_config(cfg));
+  config_delete(cfg);
+
+  /* --delete-commit selects the late whole-tree commit (delete_after) and
+     implies --delete. */
+  cfg = config_create();
+  char* argv_commit[] = {"fastsync", "--delete-commit", "/src", "/dst"};
+  positional_count = 0;
+  EXPECT_EQ_INT(parse_args(cfg, 4, argv_commit, positional_args, &positional_count), 0);
+  EXPECT_TRUE(cfg->use_delete);
+  EXPECT_TRUE(cfg->delete_after);
+  EXPECT_FALSE(cfg->delete_before);
+  EXPECT_FALSE(cfg->delete_during);
+  EXPECT_FALSE(cfg->delete_delay);
+  cfg->send_directory = str_dup("/src");
+  cfg->receive_root_directory = str_dup("/dst");
+  EXPECT_TRUE(validate_config(cfg));
+  config_delete(cfg);
+
+  /* An explicit --delete-after alongside plain --delete keeps the late timing:
+     the default never overwrites an explicit timing. */
+  cfg = config_create();
+  char* argv_after[] = {"fastsync", "--delete", "--delete-after", "/src", "/dst"};
+  positional_count = 0;
+  EXPECT_EQ_INT(parse_args(cfg, 5, argv_after, positional_args, &positional_count), 0);
+  EXPECT_TRUE(cfg->use_delete);
+  EXPECT_TRUE(cfg->delete_after);
+  EXPECT_FALSE(cfg->delete_during);
+  config_delete(cfg);
+
+  /* --delete-commit conflicts with a different timing. */
+  cfg = config_create();
+  char* argv_conflict[] = {"fastsync", "--delete-commit", "--delete-during", "/src", "/dst"};
+  positional_count = 0;
+  EXPECT_EQ_INT(parse_args(cfg, 5, argv_conflict, positional_args, &positional_count), 0);
+  EXPECT_FALSE(validate_config(cfg));
+  config_delete(cfg);
+}
+
 /* Two different delete-timing flags on one command line are a conflict, not a
  * silent last-one-wins choice. */
 static void test_parse_args_delete_timing_conflict_rejected() {
@@ -4740,6 +4815,7 @@ void test_client_cli() {
   test_parse_args_relative_no_implied_mkpath();
   test_parse_args_delete_during_alias();
   test_parse_args_delete_timing_flags();
+  test_parse_args_delete_default_timing_and_commit();
   test_parse_args_delete_timing_conflict_rejected();
   test_parse_args_delete_timing_without_delete_rejected();
   test_parse_args_rejects_unimplemented_options();
@@ -4831,6 +4907,7 @@ void test_client_cli() {
   test_parse_args_filter_rules();
   test_parse_args_from0_cvs_filter_file_flags();
   test_parse_args_basis_dirs();
+  test_parse_args_verify_basis();
   test_parse_args_basis_invalid_paths();
   test_validate_config_basis_rejects_chunk_serialization();
   test_parse_args_delete_policy_flags();

tests/test_config.c

@@ -1,6 +1,7 @@
 #include "test_config.h"
 #include "config.h"
 #include "delta.h"
+#include "filter.h"
 #include "identity.h"
 #include "multiprocessing.h"
 #include "protocol.h"
@@ -2119,6 +2120,48 @@ static void test_config_receive_rejects_oversized_string_budget() {
   config_delete(over_bytes);
 }
 
+/* Pre-auth bounds for the receiver-side filter rule block (protocol 2.28.0).
+   A peer may send `protect`/`risk` rules; the receiver must reject an over-cap
+   count or an over-long pattern before evaluating anything, so a crafted config
+   cannot drive unbounded glob work or install a rule that silently never
+   matches. */
+static void test_config_receive_rejects_bad_protect_rules() {
+  if (is_running_under_valgrind())
+    return;
+
+  /* Over-cap rule count: one more than MAX_FILTER_RULES rules. */
+  Config* c = config_create();
+  EXPECT_NOT_NULL(c);
+  c->send_directory = str_dup("/src");
+  c->receive_root_directory = str_dup("/dst");
+  c->filters = array_list_create(free);
+  EXPECT_NOT_NULL(c->filters);
+  for (int i = 0; i <= MAX_FILTER_RULES; i++)
+    EXPECT_TRUE(array_list_add(c->filters, str_dup("- *.tmp")));
+  EXPECT_TRUE(roundtrip_config_rejected(c));
+  config_delete(c);
+
+  /* A pattern longer than the receiver's evaluation bound is rejected by the
+     sender (mirroring the receiver's guard) instead of being sent as an inert
+     rule. */
+  c = config_create();
+  EXPECT_NOT_NULL(c);
+  c->send_directory = str_dup("/src");
+  c->receive_root_directory = str_dup("/dst");
+  c->filters = array_list_create(free);
+  EXPECT_NOT_NULL(c->filters);
+  size_t big = MAX_PROTECT_PATTERN_LEN + 1;
+  char* long_rule = malloc(big + 3);
+  EXPECT_NOT_NULL(long_rule);
+  long_rule[0] = '-';
+  long_rule[1] = ' ';
+  memset(long_rule + 2, 'x', big);
+  long_rule[big + 2] = '\0';
+  EXPECT_TRUE(array_list_add(c->filters, long_rule));
+  EXPECT_TRUE(roundtrip_config_rejected(c));
+  config_delete(c);
+}
+
 /* identity_copy_as_refused() is the pure, pre-snapshot refusal predicate: a
    --copy-as is refused when the receiver is not root OR the effective super
    mode is OFF (an operator veto), and never when --copy-as is unset. */
@@ -2590,6 +2633,46 @@ static bool basis_equal(const Config* a, const Config* b) {
   return true;
 }
 
+/* The receiver reconstructs its delete-protection list from the sender's
+ * compiled base rules, so compare the received list against a fresh
+ * filter_base_build() of the sender's raw --filter texts. */
+static bool filter_rules_equal(const Config* a, const FilterRuleList* got) {
+  int count = a->filters ? a->filters->size : 0;
+  const char** texts = NULL;
+  if (count > 0) {
+    texts = calloc((size_t)count, sizeof(char*));
+    if (!texts)
+      return false;
+    for (int i = 0; i < count; i++)
+      texts[i] = (const char*)a->filters->items[i];
+  }
+  char err[160];
+  FilterRuleList* expected =
+      filter_base_build(texts, count, a->cvs_exclude, a->delete_excluded, err, sizeof(err));
+  free(texts);
+  if (!expected)
+    return false;
+  bool equal = true;
+  int want = expected->count;
+  int have = got ? got->count : 0;
+  if (want != have) {
+    equal = false;
+  } else {
+    for (int i = 0; i < want; i++) {
+      const FilterRule* x = expected->items[i];
+      const FilterRule* y = got->items[i];
+      if (x->action != y->action || x->sides != y->sides || x->anchored != y->anchored ||
+          x->dir_only != y->dir_only || x->negate != y->negate ||
+          !str_opt_equal(x->owner, y->owner) || !str_opt_equal(x->pattern, y->pattern)) {
+        equal = false;
+        break;
+      }
+    }
+  }
+  filter_rule_list_free(expected);
+  return equal;
+}
+
 #define CONFIG_CMP_BOOL(a, b, name) ((a)->name == (b)->name)
 #define CONFIG_CMP_INT(a, b, name) ((a)->name == (b)->name)
 #define CONFIG_CMP_RAW(a, b, name) ((a)->name == (b)->name)
@@ -2615,6 +2698,7 @@ static bool basis_equal(const Config* a, const Config* b) {
 #define CONFIG_CMP_COPY_AS_ID(a, b, name) (!(a)->copy_as_set || (a)->name == (b)->name)
 #define CONFIG_CMP_BLOCK_SKIP_SUFFIXES(a, b, name) skip_suffixes_equal((a), (b))
 #define CONFIG_CMP_BLOCK_BASIS(a, b, name) basis_equal((a), (b))
+#define CONFIG_CMP_BLOCK_PROTECT_RULES(a, b, name) filter_rules_equal((a), (b)->name)
 #define CONFIG_CMP_BLOCK_IDMAP(a, b, name)                                                         \
   idmap_equal((a)->name, (a)->name##_count, (b)->name, (b)->name##_count)
 
@@ -2784,6 +2868,7 @@ static void golden_config_populate(Config* c) {
   c->skip_compress_suffixes[1] = str_dup(".xz");
   EXPECT_EQ_INT(config_basis_append(c, BASIS_DEST_COMPARE, "compare"), 0);
   EXPECT_EQ_INT(config_basis_append(c, BASIS_DEST_LINK, "link"), 0);
+  c->verify_basis = true;
   c->fuzzy = true;
   c->checksum_algo = CHECKSUM_ALGO_MD5;
   c->checksum_seed = 0x1122334455667788ULL;
@@ -2829,6 +2914,14 @@ static void golden_config_populate(Config* c) {
   c->copy_as_set = true;
   c->copy_as_uid = 111;
   c->copy_as_gid = 222;
+  /* Compile-through delete-protection rules (protocol 2.28.0).  The golden
+   * sender serializes its compiled base rules, so populate a diverse set that
+   * exercises both sides, negate, anchoring and dir-only. */
+  c->filters = array_list_create(free);
+  array_list_add(c->filters, str_dup("P *.log"));
+  array_list_add(c->filters, str_dup("+r **/*.txt"));
+  array_list_add(c->filters, str_dup("H,!secret"));
+  array_list_add(c->filters, str_dup("- /sub/dir/"));
 }
 
 /* The pinned golden frame (protocol 2.28.0).  The values below are the only
@@ -2836,12 +2929,14 @@ static void golden_config_populate(Config* c) {
  * them ONLY with a PROTOCOL_VERSION bump and a documented reason.  The 2.24.0
  * delete-plan wave changed only the version string; 2.25.0 appended the
  * report_stats bool, 2.26.0 appended the compression_algo int, 2.27.0 appended
- * the report_deletes bool, and 2.28.0 changed only the version string (the
- * STATUS_STATS body grew, but the config frame layout is unchanged, so the
- * frame length is identical).  The byte-exact values are recomputed for the
- * merged layout. */
-#define GOLDEN_WIRE_LEN 709
-#define GOLDEN_WIRE_HASH 417335736347473203ULL
+ * the report_deletes bool, and 2.28.0 changed only the version string and
+ * appended the receiver-side delete-protection rule block (the STATUS_STATS
+ * body also grew, but that is not part of this frame).  Track 5a appends the
+ * FastSync-only verify_basis bool to the basis block WITHOUT a version bump
+ * (project decision), so the frame grew by one int to 886 bytes.  The
+ * byte-exact values are recomputed for the merged layout. */
+#define GOLDEN_WIRE_LEN 886
+#define GOLDEN_WIRE_HASH 5809509022716816757ULL
 
 static unsigned long long fnv1a_64(const unsigned char* buf, size_t len) {
   unsigned long long h = 1469598103934665603ULL;
@@ -2990,6 +3085,7 @@ static void test_config_wire_golden_receive() {
            recv->groupmap[0].to_name != NULL && strcmp(recv->groupmap[0].to_name, "root") == 0;
       ok = ok && recv->basis_count == 2 && recv->basis_dirs[0].type == BASIS_DEST_COMPARE &&
            recv->basis_dirs[1].type == BASIS_DEST_LINK;
+      ok = ok && recv->verify_basis;
       ok = ok && recv->module != NULL && strcmp(recv->module, "goldenmod") == 0;
       ok = ok && recv->copy_as_set && recv->copy_as_uid == 111 && recv->copy_as_gid == 222;
     }
@@ -3250,6 +3346,7 @@ void test_config() {
     test_config_wire_golden_receive();
     test_config_wire_receive_bounds();
     test_config_receive_rejects_overcap_counts();
+    test_config_receive_rejects_bad_protect_rules();
     test_config_wire_roundtrip_all_fields();
     test_config_preserve_attribute_wire_roundtrip();
   }

tests/test_delete_plan.c

@@ -17,6 +17,7 @@
  * caller/receiver entry point) describing `dir` with no kept children. */
 static void send_plan_frame(int fd, const char* dir) {
   EXPECT_TRUE(send_int(fd, 0)); /* has_config */
+  EXPECT_TRUE(send_int(fd, 1)); /* apply: a real plan */
   EXPECT_TRUE(send_wire_str(fd, dir));
   EXPECT_TRUE(send_int(fd, 0)); /* kept child dirs */
   EXPECT_TRUE(send_int(fd, 0)); /* kept child files */
@@ -216,9 +217,58 @@ static void test_delete_delay_actual_removal_charges_budget(void) {
   config_delete(config);
 }
 
+/* Send a config-only carrier frame (apply=false): the per-run config block with
+ * one --delete-missing-args exact path, and no directory walk. */
+static void send_config_only_frame(int fd, const char* missing_path) {
+  EXPECT_TRUE(send_int(fd, 1)); /* has_config */
+  EXPECT_TRUE(send_int(fd, 0)); /* protected prefixes */
+  EXPECT_TRUE(send_int(fd, 0)); /* size-skipped */
+  EXPECT_TRUE(send_int(fd, 1)); /* missing args */
+  EXPECT_TRUE(send_wire_str(fd, missing_path));
+  EXPECT_TRUE(send_int(fd, 0)); /* apply = false */
+  EXPECT_TRUE(send_wire_str(fd, "."));
+  EXPECT_TRUE(send_int(fd, 0));
+  EXPECT_TRUE(send_int(fd, 0));
+}
+
+/* The config-only carrier frame (apply=false) still applies the
+ * --delete-missing-args exact deletions even though it walks no directory.  This
+ * is the fix for a --files-from list that synchronizes no directory. */
+static void test_config_only_frame_applies_missing_args(void) {
+  char root[] = "/tmp/fastsync_dp_cfgonly_XXXXXX";
+  EXPECT_TRUE(mkdtemp(root) != NULL);
+  char gone[1024];
+  snprintf(gone, sizeof(gone), "%s/gone.txt", root);
+  int fd = open(gone, O_WRONLY | O_CREAT | O_TRUNC, 0600);
+  EXPECT_TRUE(fd >= 0);
+  close(fd);
+
+  Config* config = config_create();
+  EXPECT_NOT_NULL(config);
+  config->receive_root_directory = str_dup(root);
+  config->delete_missing_args = true;
+
+  int p[2];
+  EXPECT_EQ_INT(socketpair(AF_UNIX, SOCK_STREAM, 0, p), 0);
+
+  DeletePlanSession* session = delete_plan_session_create(config);
+  EXPECT_NOT_NULL(session);
+  send_config_only_frame(p[1], "gone.txt");
+  EXPECT_EQ_INT(delete_plan_session_receive(session, config, p[0]), 0);
+  EXPECT_EQ_INT((int)delete_plan_session_deleted(session), 1);
+  EXPECT_TRUE(lstat(gone, &(struct stat){0}) != 0);
+
+  delete_plan_session_destroy(session);
+  close(p[0]);
+  close(p[1]);
+  rmdir(root);
+  config_delete(config);
+}
+
 void test_delete_plan(void) {
   test_delete_delay_refilled_dir_removed_recursively();
   test_delete_delay_removed_file_counted();
   test_delete_delay_max_delete_bounds_actual();
   test_delete_delay_actual_removal_charges_budget();
+  test_config_only_frame_applies_missing_args();
 }

tests/test_file.c

@@ -6,6 +6,7 @@
 #include "file_receive.h"
 #include "data.h"
 #include "config.h"
+#include "charset.h"
 #include "utils.h"
 #include "protocol.h"
 #include "test_utils.h"
@@ -1807,6 +1808,159 @@ static void test_receive_incremental_check_empty_path() {
   config_delete(cfg);
 }
 
+/* Pure policy helpers behind the basis quick-check / --verify-basis decision. */
+static void test_file_basis_quick_match_decision() {
+  Config* cfg = config_create();
+  EXPECT_NOT_NULL(cfg);
+  EXPECT_FALSE(file_basis_content_required(cfg));
+  cfg->verify_basis = true;
+  EXPECT_TRUE(file_basis_content_required(cfg));
+  cfg->verify_basis = false;
+
+  struct stat st;
+  memset(&st, 0, sizeof(st));
+  st.st_mtime = 1500000000;
+#ifdef __linux__
+  st.st_mtim.tv_nsec = 500;
+#endif
+  /* Equal size is required by the caller; this leg is the mtime / --size-only
+     rule.  Equal mtime matches, a different mtime misses by default. */
+  EXPECT_TRUE(file_basis_quick_match(cfg, &st, 1500000000, 500));
+  EXPECT_FALSE(file_basis_quick_match(cfg, &st, 1500000001, 500));
+  cfg->size_only = true;
+  EXPECT_TRUE(file_basis_quick_match(cfg, &st, 1500000001, 500));
+  cfg->size_only = false;
+  cfg->modify_window = 2;
+  EXPECT_TRUE(file_basis_quick_match(cfg, &st, 1500000002, 500));
+  config_delete(cfg);
+}
+
+/* End-to-end handshake decision for a same-size, same-mtime, DIFFERENT-content
+   basis.  Default (rsync parity): the metadata quick-check is trusted, the
+   receiver answers STATUS_OK and materializes the basis bytes.  --verify-basis:
+   the whole-file digest is required, the basis is rejected and the receiver
+   asks for the source (STATUS_NEXT + full transfer). */
+static void test_receive_incremental_check_basis_quick_check_and_verify() {
+  const char* root = "test_basis_quick_root";
+  const char* basis_dir = "test_basis_quick_root/basis";
+  const char* basis_file = "test_basis_quick_root/basis/f.txt";
+  unlink(basis_file);
+  unlink("test_basis_quick_root/f.txt");
+  rmdir(basis_dir);
+  rmdir(root);
+  EXPECT_EQ_INT(mkdir(root, 0755), 0);
+  EXPECT_EQ_INT(mkdir(basis_dir, 0755), 0);
+
+  const char* src_bytes = "AAAA";
+  const unsigned long long size = 4;
+  const time_t mtime = 1500000000;
+  {
+    FILE* fh = fopen(basis_file, "wb");
+    EXPECT_NOT_NULL(fh);
+    // cppcheck-suppress knownConditionTrueFalse
+    if (fh) {
+      EXPECT_EQ_INT((int)fwrite("BBBB", 1, (size_t)size, fh), (int)size);
+      fclose(fh);
+    }
+  }
+  struct timespec ts[2] = {{mtime, 0}, {mtime, 0}};
+  EXPECT_EQ_INT(utimensat(AT_FDCWD, basis_file, ts, 0), 0);
+
+  char root_abs[PATH_MAX];
+  EXPECT_NOT_NULL(realpath(root, root_abs));
+  int root_fd = open(root_abs, O_RDONLY | O_DIRECTORY | O_CLOEXEC);
+  EXPECT_TRUE(root_fd >= 0);
+  // cppcheck-suppress knownConditionTrueFalse
+  if (root_fd < 0) {
+    unlink(basis_file);
+    rmdir(basis_dir);
+    rmdir(root);
+    return;
+  }
+  EXPECT_TRUE(utils_set_authorized_root(root_fd, root_abs));
+
+  uint8_t digest[CHECKSUM_MAX_DIGEST_LEN];
+  size_t digest_len = 0;
+  EXPECT_TRUE(checksum_digest(CHECKSUM_ALGO_XXH64, 0, src_bytes, size, digest, sizeof(digest),
+                              &digest_len));
+
+  /* Route protocol I/O through the explicit descriptors (a previous test group
+     may have left io_set_fds() bound to its own pipe). */
+  io_set_fds(-1, -1);
+  io_set_bwlimit(0);
+
+  for (int verify = 0; verify <= 1; verify++) {
+    Config* cfg = config_create();
+    EXPECT_NOT_NULL(cfg);
+    cfg->receive_root_directory = str_dup(root_abs);
+    cfg->checksum = false;
+    cfg->checksum_algo = CHECKSUM_ALGO_XXH64;
+    cfg->checksum_seed = 0;
+    cfg->use_incremental = true;
+    cfg->use_delta = false;
+    cfg->use_metadata = false;
+    cfg->verify_basis = (verify != 0);
+    EXPECT_EQ_INT(config_basis_append(cfg, BASIS_DEST_LINK, "basis"), 0);
+
+    int p[2];
+    EXPECT_EQ_INT(socketpair(AF_UNIX, SOCK_STREAM, 0, p), 0);
+    EXPECT_TRUE(send_wire_str(p[1], "f.txt"));
+    unsigned long long check_size = size;
+    long long check_mtime = (long long)mtime;
+    long long check_mtime_nsec = 0;
+    EXPECT_TRUE(send_n_data(p[1], &check_size, sizeof(check_size)));
+    EXPECT_TRUE(send_n_data(p[1], &check_mtime, sizeof(check_mtime)));
+    EXPECT_TRUE(send_n_data(p[1], &check_mtime_nsec, sizeof(check_mtime_nsec)));
+    /* Only --verify-basis needs the digest (cfg->checksum is false) and the
+       pre-staged fallback full transfer the receiver will request. */
+    if (verify) {
+      uint8_t wire_len = (uint8_t)digest_len;
+      EXPECT_TRUE(send_n_data(p[1], &wire_len, sizeof(wire_len)));
+      EXPECT_TRUE(send_n_data(p[1], digest, digest_len));
+      char* payload_bytes = str_dup(src_bytes);
+      EXPECT_NOT_NULL(payload_bytes);
+      Data* payload = data_create(payload_bytes, size);
+      EXPECT_NOT_NULL(payload);
+      // cppcheck-suppress knownConditionTrueFalse
+      if (payload)
+        EXPECT_TRUE(send_data(p[1], payload));
+      data_destroy(payload);
+    }
+
+    bool skipped = false;
+    File* file = receive_incremental_check(p[0], cfg, &skipped);
+    EXPECT_NOT_NULL(file);
+    // cppcheck-suppress knownConditionTrueFalse
+    if (file) {
+      EXPECT_FALSE(skipped);
+      Status reply = STATUS_ERROR;
+      EXPECT_TRUE(receive_status(p[1], &reply));
+      if (verify) {
+        EXPECT_EQ_INT((int)reply, (int)STATUS_NEXT);
+        EXPECT_NOT_NULL(file->data->data);
+        EXPECT_TRUE(file->data->data != NULL && memcmp(file->data->data, src_bytes, size) == 0);
+      } else {
+        EXPECT_EQ_INT((int)reply, (int)STATUS_OK);
+        EXPECT_TRUE(file->skip);
+        /* The default quick-check hit materializes from the basis PATH at
+           install time (streaming), so no content is buffered on the File. */
+        EXPECT_NOT_NULL(file->basis_link);
+        EXPECT_NULL(file->data->data);
+      }
+      file_destroy(file);
+    }
+    close(p[0]);
+    close(p[1]);
+    config_delete(cfg);
+  }
+
+  utils_set_authorized_root(-1, NULL);
+  close(root_fd);
+  unlink(basis_file);
+  rmdir(basis_dir);
+  rmdir(root);
+}
+
 /* -K/--keep-dirlinks secure open: with an authorized root, a destination path
  * component that is a symlink to an IN-ROOT directory is used as that directory
  * (its referent is opened through a relative O_NOFOLLOW walk from the root fd,
@@ -2140,6 +2294,8 @@ void test_file() {
   test_dir_time_list();
   test_dir_time_list_cap();
   test_receive_incremental_check_empty_path();
+  test_file_basis_quick_match_decision();
+  test_receive_incremental_check_basis_quick_check_and_verify();
   test_keep_dirlinks_secure_open();
   test_inplace_overwrite_clears_special_mode_bits();
   test_inplace_overwrite_metadata_strips_special_bits();

tests/test_fuzz_smoke.c

@@ -18,10 +18,11 @@
 
 /* P8 config-frame tail: super_mode (4) + copy-as presence (4) + uid (4) + gid (4). */
 #define P8_TAIL_BYTES 16
-/* Bytes after the P8 tail: report_dest_info (4), report_stats (4, wire-stats
- * wave) and compression_algo (4, codec wave).  The P8 fields sit this many
- * bytes before the end of the frame. */
-#define POST_P8_TAIL_BYTES 12
+/* Bytes after the P8 tail: report_dest_info (4), report_stats (4),
+ * report_deletes (4, --info=del wave), compression_algo (4, codec wave) and the
+ * receiver delete-protection count (4, protocol 2.28.0).  The P8 fields sit
+ * this many bytes before the end of the frame. */
+#define POST_P8_TAIL_BYTES 20
 
 /* Smoke test for chunk_deserialize fuzz target */
 static void test_fuzz_chunk_deserialize() {

tests/test_server.c

@@ -1063,14 +1063,18 @@ static void test_incremental_check_fifo_destination_does_not_hang() {
 }
 
 /* A server-contacting --dry-run with an alternate basis dir must never read or
-   hash the basis file.  An exact (size+mtime+content) basis match would
-   otherwise let a client probe the basis bytes against its own supplied digest
-   (a 1-bit content oracle).  The dry-run decision is metadata-only, so even a
-   byte-identical basis is reported as would-transfer, not a compare-dest skip. */
-static void test_incremental_check_dry_run_basis_does_not_read_content() {
+   hash the basis file.  Under the default metadata quick-check a hit needs no
+   basis bytes, so a compare-dest match is reported as a skip (STATUS_OK) just
+   like a real run -- and still no content is read.  Under --verify-basis a hit
+   would require hashing the basis against the client-supplied digest (a 1-bit
+   content oracle), which a dry-run must never do, so even a byte-identical
+   basis is reported as would-transfer.  The destination is never materialized
+   in either arm. */
+static void run_dry_run_basis_check(bool verify, Status expected) {
   Config* cfg = config_create();
   EXPECT_NOT_NULL(cfg);
   cfg->dry_run = true;
+  cfg->verify_basis = verify;
   char* root = make_check_root("dryb");
   EXPECT_NOT_NULL(root);
   cfg->receive_root_directory = str_dup(root);
@@ -1086,8 +1090,8 @@ static void test_incremental_check_dry_run_basis_does_not_read_content() {
   EXPECT_EQ_INT(stat(basis_path, &bst), 0);
   EXPECT_EQ_INT(config_basis_append(cfg, BASIS_DEST_COMPARE, "basis"), 0);
 
-  /* The (correct) source digest for the basis bytes: an unfixed dry-run would
-     read+hash the basis and treat this as an exact compare-dest hit. */
+  /* The (correct) source digest for the basis bytes: a buggy dry-run that read
+     and hashed the basis would treat this as an exact compare-dest hit. */
   uint8_t digest[CHECKSUM_MAX_DIGEST_LEN];
   size_t digest_len = 0;
   EXPECT_TRUE(checksum_digest((ChecksumAlgo)cfg->checksum_algo, cfg->checksum_seed, content,
@@ -1106,7 +1110,8 @@ static void test_incremental_check_dry_run_basis_does_not_read_content() {
     bool skipped = false;
     bool would_transfer = false;
     File* file = receive_incremental_check_ex(p[0], cfg, &skipped, &would_transfer);
-    bool ok = file == NULL && !skipped && would_transfer;
+    bool ok = file == NULL && skipped == (expected == STATUS_OK) &&
+              would_transfer == (expected != STATUS_OK);
     file_destroy(file);
     config_delete(cfg);
     close(p[0]);
@@ -1124,13 +1129,16 @@ static void test_incremental_check_dry_run_basis_does_not_read_content() {
     EXPECT_TRUE(send_n_data(p[1], &size, sizeof(size)));
     EXPECT_TRUE(send_n_data(p[1], &mtime, sizeof(mtime)));
     EXPECT_TRUE(send_n_data(p[1], &mtime_nsec, sizeof(mtime_nsec)));
-    uint8_t wire_len = (uint8_t)digest_len;
-    EXPECT_TRUE(send_n_data(p[1], &wire_len, sizeof(wire_len)));
-    EXPECT_TRUE(send_n_data(p[1], digest, digest_len));
+    /* The digest is only on the wire when --checksum or --verify-basis needs it
+       (cfg->checksum is false here); the default quick-check arm sends none. */
+    if (verify) {
+      uint8_t wire_len = (uint8_t)digest_len;
+      EXPECT_TRUE(send_n_data(p[1], &wire_len, sizeof(wire_len)));
+      EXPECT_TRUE(send_n_data(p[1], digest, digest_len));
+    }
     Status s;
     EXPECT_TRUE(receive_status(p[1], &s));
-    /* A skip here would mean the receiver read+hashed the basis file. */
-    EXPECT_EQ_INT(s, STATUS_DRY_RUN_TRANSFER);
+    EXPECT_EQ_INT(s, expected);
 
     int status;
     waitpid(pid, &status, 0);
@@ -1148,6 +1156,11 @@ static void test_incremental_check_dry_run_basis_does_not_read_content() {
   }
 }
 
+static void test_incremental_check_dry_run_basis_does_not_read_content() {
+  run_dry_run_basis_check(false, STATUS_OK);
+  run_dry_run_basis_check(true, STATUS_DRY_RUN_TRANSFER);
+}
+
 /* B1: a FIFO planted in a --link-dest basis directory must not block
  * basis_open_regular() either; the basis match is simply declined. */
 static void test_incremental_check_basis_fifo_does_not_hang() {
@@ -1278,6 +1291,7 @@ static void test_dry_run_delete_plan_commit_does_not_delete() {
   EXPECT_TRUE(send_int(p[1], 0)); /* size-skipped prefixes */
   EXPECT_TRUE(send_int(p[1], 1)); /* missing-args exact deletions */
   EXPECT_TRUE(send_str(p[1], "victim.txt"));
+  EXPECT_TRUE(send_int(p[1], 1));   /* apply: a real plan */
   EXPECT_TRUE(send_str(p[1], ".")); /* receive root plan */
   EXPECT_TRUE(send_int(p[1], 0));   /* kept child directories */
   EXPECT_TRUE(send_int(p[1], 0));   /* kept child files */

tests/test_shared_utils.c

@@ -138,7 +138,7 @@ static void test_walker_removes_extras_keeps_manifest_and_protected() {
   DeleteSkipEntry skip = {"prot", false};
   size_t deleted = 0;
   DeleteWalkResult result =
-      delete_extras_limited(root, manifest, NULL, 100000, &skip, 1, &deleted, NULL);
+      delete_extras_limited(root, manifest, NULL, 100000, &skip, 1, NULL, &deleted, NULL);
   EXPECT_EQ_INT((int)result, (int)DELETE_WALK_OK);
   EXPECT_FALSE(file_exists(root, "a.txt"));
   EXPECT_TRUE(file_exists(root, "keep.txt"));
@@ -173,7 +173,7 @@ static void test_walker_keeps_nested_manifest_dirs() {
   EXPECT_NOT_NULL(manifest);
   size_t deleted = 0;
   DeleteWalkResult result =
-      delete_extras_limited(root, manifest, NULL, 100000, NULL, 0, &deleted, NULL);
+      delete_extras_limited(root, manifest, NULL, 100000, NULL, 0, NULL, &deleted, NULL);
   EXPECT_EQ_INT((int)result, (int)DELETE_WALK_OK);
   EXPECT_FALSE(file_exists(root, "extra.txt"));
   EXPECT_TRUE(file_exists(root, "keepdir/deep/keep.txt"));
@@ -204,7 +204,7 @@ static void test_walker_max_delete_partial_deletes_up_to_cap() {
   size_t deleted = 999;
   size_t skipped = 0;
   DeleteWalkResult result =
-      delete_extras_limited(root, manifest, NULL, 2, NULL, 0, &deleted, &skipped);
+      delete_extras_limited(root, manifest, NULL, 2, NULL, 0, NULL, &deleted, &skipped);
   EXPECT_EQ_INT((int)result, (int)DELETE_WALK_LIMIT_REACHED);
   EXPECT_EQ_INT((int)deleted, 2);
   EXPECT_EQ_INT((int)skipped, 1);
@@ -225,7 +225,8 @@ static void test_walker_max_delete_exact_bound_deletes() {
   ArrayList* manifest = make_manifest_strings(keeps, 0);
   EXPECT_NOT_NULL(manifest);
   size_t deleted = 0;
-  DeleteWalkResult result = delete_extras_limited(root, manifest, NULL, 2, NULL, 0, &deleted, NULL);
+  DeleteWalkResult result =
+      delete_extras_limited(root, manifest, NULL, 2, NULL, 0, NULL, &deleted, NULL);
   EXPECT_EQ_INT((int)result, (int)DELETE_WALK_OK);
   EXPECT_EQ_INT((int)deleted, 2);
   EXPECT_FALSE(file_exists(root, "a.txt"));
@@ -258,7 +259,7 @@ static void test_walker_removes_extraneous_symlinks() {
   EXPECT_NOT_NULL(manifest);
   size_t deleted = 0;
   DeleteWalkResult result =
-      delete_extras_limited(root, manifest, NULL, 100000, NULL, 0, &deleted, NULL);
+      delete_extras_limited(root, manifest, NULL, 100000, NULL, 0, NULL, &deleted, NULL);
   EXPECT_EQ_INT((int)result, (int)DELETE_WALK_OK);
   EXPECT_FALSE(file_exists(root, "link_file"));
   EXPECT_FALSE(file_exists(root, "link_dir"));
@@ -294,7 +295,7 @@ static void test_walker_confines_deletion_to_synced_dirs() {
   EXPECT_TRUE(array_list_add(dirs, str_dup("inscope")));
   size_t deleted = 0;
   DeleteWalkResult result =
-      delete_extras_limited(root, manifest, dirs, 100000, NULL, 0, &deleted, NULL);
+      delete_extras_limited(root, manifest, dirs, 100000, NULL, 0, NULL, &deleted, NULL);
   EXPECT_EQ_INT((int)result, (int)DELETE_WALK_OK);
   EXPECT_TRUE(file_exists(root, "rootextra.txt"));
   EXPECT_FALSE(file_exists(root, "inscope/extra.txt"));
@@ -324,6 +325,45 @@ static void test_walker_unlimited_deletes_all() {
   free(root);
 }
 
+/* Receiver-side filter protection (protocol 2.28.0): a compiled protect rule
+   shields a DESTINATION-ONLY extra that never appeared on the sender, a risk
+   rule cancels an earlier/later protect (first match wins), and a dir-only
+   protect rule shields the whole subtree. */
+static void test_walker_protect_rules_shield_dest_only() {
+  char* root = make_walk_root("protectrules");
+  EXPECT_NOT_NULL(root);
+  EXPECT_TRUE(write_file_at(root, "keep.txt", "kept"));
+  EXPECT_TRUE(write_file_at(root, "extra.log", "risk cancels protect"));
+  EXPECT_TRUE(write_file_at(root, "safe.log", "protected"));
+  EXPECT_TRUE(write_file_at(root, "other.txt", "deleted"));
+  EXPECT_EQ_INT(make_subdir(root, "prot"), 0);
+  EXPECT_TRUE(write_file_at(root, "prot/inside.txt", "shielded subtree"));
+  EXPECT_TRUE(write_file_at(root, "prot/deep.log", "shielded subtree"));
+
+  const char* keeps[] = {"keep.txt"};
+  ArrayList* manifest = make_manifest_strings(keeps, 1);
+  EXPECT_NOT_NULL(manifest);
+  const char* rule_text[] = {"R extra.log", "P *.log", "P prot/"};
+  char err[160];
+  FilterRuleList* rules = filter_base_build(rule_text, 3, false, false, err, sizeof(err));
+  EXPECT_NOT_NULL(rules);
+  size_t deleted = 0;
+  DeleteWalkResult result =
+      delete_extras_limited(root, manifest, NULL, 100000, NULL, 0, rules, &deleted, NULL);
+  EXPECT_EQ_INT((int)result, (int)DELETE_WALK_OK);
+  EXPECT_TRUE(file_exists(root, "keep.txt"));
+  EXPECT_FALSE(file_exists(root, "extra.log")); /* risk wins the first match */
+  EXPECT_TRUE(file_exists(root, "safe.log"));   /* protect shields the extra */
+  EXPECT_FALSE(file_exists(root, "other.txt"));
+  EXPECT_TRUE(dir_exists(root, "prot"));
+  EXPECT_TRUE(file_exists(root, "prot/inside.txt"));
+  EXPECT_TRUE(file_exists(root, "prot/deep.log"));
+  filter_rule_list_free(rules);
+  array_list_delete(manifest);
+  remove_walk_tree(root);
+  free(root);
+}
+
 typedef struct {
   bool eight_bit_output;
   const char* expected;
@@ -626,6 +666,7 @@ void test_shared_utils() {
   test_walker_removes_extraneous_symlinks();
   test_walker_confines_deletion_to_synced_dirs();
   test_walker_unlimited_deletes_all();
+  test_walker_protect_rules_shield_dest_only();
   test_loopback_helpers();
   test_fd_peer_ip();
 

tests/test_xattr.c

@@ -210,7 +210,8 @@ static void test_xattr_receive_drops_acl_without_preserve_acls() {
 
 /* MINOR-2: a --link-dest / -H copy fallback (linkat refused) must still apply
  * the per-file xattrs and --fake-super stat.  A DIRECTORY basis forces linkat
- * to fail with EPERM, exercising the byte-copy fallback deterministically.
+ * to fail with EPERM, exercising the byte-copy fallback deterministically (the
+ * basis is not a regular file, so the fallback uses the caller's bytes).
  * Guarded on filesystem xattr support. */
 static void test_link_copy_fallback_preserves_xattrs() {
   const char* dest = "test_link_xattr_dest.txt";