feat(progress): opt-in paths-only pre-count for rsync to-chk parity

- when --progress/--info=progress is requested, a metadata-only pre-scan
  builds the full file-list total and directory names so the to-chk
  denominator counts every regular/dir/link/special entry like rsync
- per-directory/symlink/special name lines emitted; sequential and --threads
- reuses the --delete-during/delay pre-scan when present; non-progress runs
  take no extra pass
- --progress stays a caveat (emission order still differs); single-file output
  remains byte-identical

RSYNC_COMPAT.md

@@ -39,6 +39,8 @@ 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 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 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
@@ -85,7 +87,7 @@ Every one of those has an entry below with its remaining caveats.
 | `--stats` | Give transfer stats | ⚠️ Caveat | Prints transfer statistics. Protocol 2.25.0 populates the receiver-only counters the sender cannot observe (`Matched data`, `Number of deleted files`) from the receiver's `STATUS_STATS` report; the sender tracks the scanned file list per type so `Number of files` carries rsync's `(reg: X, dir: Y, link: Z, special: W)` breakdown (directories come from the scanner's captured directory list, present for `-a`/`-t`/`-p`), `Number of regular files transferred` excludes symlinks/specials and up-to-date files, `Total file size` includes symlink target lengths, and `Total transferred file size` counts only transferred files. **Protocol 2.28.0 extends `STATUS_STATS`** with receiver-observed `literal_bytes` and the four `created_*` counters: `Number of created files` now carries rsync's `(reg/dir/link/special)` breakdown (the receiver reports which destination entries it newly created, including implicitly-created parent directories below the transfer root) and `Literal data` is exact for a delta transfer (the receiver counts the literal fragments it stored, not the whole source size) — all differential-tested in the sequential and `--threads` paths against rsync 3.4.1 for fresh-create, update and delta shapes. **Remaining divergences:** a recursive scan that preserves no directory attribute (`-r` without `-t`/`-p`) captures no directory entries, so the `dir:` category is then omitted from `Number of files`; rsync's per-type breakdown on `Number of deleted files` is not reproduced; and `Total bytes sent`/`received` are FastSync wire bytes framed differently from rsync's, so they are not numerically comparable |
 | `-h`, `--human-readable` | Human-readable numbers | ✅ Parity | Formats transfer byte and rate counts using rsync's **decimal** (base-1000) units, matching rsync `-h` (e.g. `1.23M`), not binary units. **A lone `-h` with no transfer arguments prints help instead** (protocol 2.26.0), matching the rsync idiom; `-h` alongside a transfer remains human-readable |
 | `-i`, `--itemize-changes` | Per-file change summary | ✅ Parity | Prints rsync-style `>f+++++++++` lines to stdout only for files actually sent (also under `-j`/`--threads`); unchanged files print nothing, matching single-`-i` behavior |
-| `--progress` | Show progress | ⚠️ Caveat | Protocol 2.25.0 prints rsync-style per-file progress blocks (percent, transferred/total bytes, rate, elapsed, `(xfr#N, to-chk=M/T)`) fed by the receiver's `STATUS_STATS`, in both the sequential and `--threads` send paths. FastSync now also prints rsync's leading `./` transfer-root line and counts that root entry in the `to-chk` denominator, so a **single-file transfer's name lines and deterministic frames are byte-identical to rsync** (differential test). **Remaining divergences:** for a multi-directory tree rsync prints a per-directory name line and its `to-chk` denominator includes every directory/symlink/special entry; FastSync's streaming scan emits only file-name lines and counts just the root plus transferred files (a full flist pre-count would be needed), and the rate/ETA are wall-clock dependent |
+| `--progress` | Show progress | ⚠️ Caveat | Protocol 2.25.0 prints rsync-style per-file progress blocks (percent, transferred/total bytes, rate, elapsed, `(xfr#N, to-chk=M/T)`) fed by the receiver's `STATUS_STATS`, in both the sequential and `--threads` send paths. FastSync also prints rsync's leading `./` transfer-root line and, when progress is requested (`--progress`/`-P`/`--info=progress`) and not `--quiet`, runs a **paths-only metadata pre-scan** (no file reads, no hashing) that supplies rsync's file-list total `T` for the `to-chk` denominator and the directory names; `--delete-during`/`--delete-delay` reuse their existing keep-set pre-scan instead of walking twice, and non-progress runs are untouched. Per-directory name lines are emitted (trailing `/`), and symlink (` -> target`) and special entries are named too, so a **fresh multi-directory tree's name set and `to-chk` denominator match rsync 3.4.1** (differential test, sequential and `--threads`) and a **single-file transfer's name lines and deterministic frames remain byte-identical** to rsync. **Remaining divergences:** rsync emits entries in sorted depth-first order while FastSync streams them in the scanner's readdir/BFS order, so the interleaving and the `to-chk` numerator differ (the denominator matches); the leading `./` root line is emitted unconditionally rather than keyed off rsync's root-attribute-change decision, and an ancestor directory line is emitted whenever a child transfers (rsync suppresses it when the directory itself is unchanged); on a re-run, entries without a quick-check (symlinks, empty directories) are still named where rsync stays silent; and the rate/ETA are wall-clock dependent |
 | `-P` | Same as --partial --progress | ✅ Parity | Parses to `--partial` + `--progress`. The independent `--partial` retention semantics are rsync parity: an interrupted write retains the already-written temp at the destination (best-effort) so a later `--append`/`--append-verify` can resume. Progress presentation is owned by the `--progress` row; there is no separate `-P` divergence |
 | `--out-format=FORMAT` | Custom output format | ❌ Divergent | Per-transfer template on stdout; tokens `%f` `%n` `%l` `%b` `%c` `%C` `%i` `%M` `%o` `%U` `%G` `%t` `%%`. `%C` now uses the negotiated transfer algorithm (`--checksum-choice`, default `xxh128`, seed 0) and renders every algorithm exactly 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. `%f`/`%n`/`%l`/`%i`/`%M`/`%U`/`%G`/`%B` also match. **Reclassified because `%b`/`%c` are protocol-specific and cannot match:** a differential against rsync 3.4.1 shows whole-file `%c = 16` for both, but rsync whole-file `%b = filesize + 27 + transfer-digest-bytes` (39 for a 0-byte file; 43/35/47 for xxh128/xxh64/sha1 on a 12-byte file) while FastSync `%b` counts its own framing; in delta mode rsync `%c = 16 + 6·ceil(filesize/block_size)` (verified at block sizes 512/700/1024/2048) while FastSync counts its own signature handshake, and rsync `%b` is its token stream. FastSync's wire bytes are a different quantity, so exact `%b`/delta-`%c` equality is impossible |
 | `--log-file=FILE` | Log to file | ✅ Parity | `log_file` config field |