Pure structural split of src/shared/file_receive.c into focused translation
units behind the unchanged file_receive.h facade:
- file_save.c : save-to-disk, special nodes, --delay-updates staging
- incremental_check.c : xattr/delta/basis/fuzzy receive + check state machine
- delete_commit.c : manifest receive + delete budget walkers
- file_receive.c : wire receive dispatch + deferred dir metadata
The shared receive_file_xattrs helper and MAX_FILE_DATA_SIZE are declared in
incremental_check.h. file_save_to_disk_full_ex is decomposed into static
helpers (validation, special dispatch, dir/symlink creation, path resolution,
pre-write policies, data install) routed through one cleanup epilogue.
No behavior change.
Move the filter rule-tree/context helpers and entry inspection into
scanner_filter.c, the parallel scanner into scanner_parallel.c, and keep
the sequential scanner in scanner.c. Shared internal declarations live in
the new scanner_internal.h; scanner.h stays the public façade.
Decompose directory_scanner_next into static helpers (skipped-entry,
selection-protection, mount/-x, directory-finish and per-entry handlers)
with no semantic change.
Move the stats/progress reporting, scanner-preparation/scan helpers and
manifest/list/dry-run senders out of the ~3.9k-line client_send.c into
client_report.c, client_scan.c and client_manifest.c, sharing declarations
through the new internal client_send_internal.h. client_send.c keeps the
transfer orchestration and is now ~2.1k lines.
Decompose the monolithic send_files into static phase helpers
(send_files_prepare/_prepare_delete/_run/_finalize/_cleanup) driven by a
single SendFilesState; ownership, ordering and exit codes are unchanged.
No behavior change.