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Align CLI supported options list with help#2020

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oferchen merged 1 commit into
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implement-missing-features-for-rsync-parity
Nov 7, 2025
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Align CLI supported options list with help#2020
oferchen merged 1 commit into
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implement-missing-features-for-rsync-parity

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@oferchen oferchen commented Nov 7, 2025

Summary

  • expand the CLI supported options list constant to enumerate the full set of flags advertised by the help text, including the new address and stop controls
  • add a regression test that parses the rendered help output and asserts every documented flag appears in the supported-options diagnostic

Testing

  • cargo test -p oc-rsync-cli

Codex Task

@oferchen oferchen merged commit 9fe451c into master Nov 7, 2025
@oferchen oferchen deleted the implement-missing-features-for-rsync-parity branch November 7, 2025 14:50
oferchen added a commit that referenced this pull request Apr 30, 2026
Audit of `crates/checksums/src/strong/` (excluding `strategy/`,
`md4_tests.rs`, `xxh64_tests.rs` per task scope). Production source files
are already well-documented from prior cleanup passes: every public type,
trait, function, and method carries rustdoc; upstream rsync references
(`upstream: checksum.c:get_checksum2()` and similar) are preserved on the
seed-handling paths in `md4.rs` and `md5.rs`; no decorative banners,
debug checkpoints, or commented-out code remain in scope.

The single substantive change in this pass adds a quirk comment to the
private `detect()` helper in `openssl_support.rs` that captures
non-obvious upstream behaviour: MD4 may be absent on OpenSSL builds
without the legacy provider, so the MD4 probe is best-effort and overall
detection succeeds as long as MD5 works. This explains the
otherwise-mysterious `if let Some(md4) = ...` whose result is
deliberately discarded.

No behaviour, signature, or import changes.
oferchen added a commit that referenced this pull request Apr 30, 2026
…) (#3469)

Audit of `crates/checksums/src/strong/` (excluding `strategy/`,
`md4_tests.rs`, `xxh64_tests.rs` per task scope). Production source files
are already well-documented from prior cleanup passes: every public type,
trait, function, and method carries rustdoc; upstream rsync references
(`upstream: checksum.c:get_checksum2()` and similar) are preserved on the
seed-handling paths in `md4.rs` and `md5.rs`; no decorative banners,
debug checkpoints, or commented-out code remain in scope.

The single substantive change in this pass adds a quirk comment to the
private `detect()` helper in `openssl_support.rs` that captures
non-obvious upstream behaviour: MD4 may be absent on OpenSSL builds
without the legacy provider, so the MD4 probe is best-effort and overall
detection succeeds as long as MD5 works. This explains the
otherwise-mysterious `if let Some(md4) = ...` whose result is
deliberately discarded.

No behaviour, signature, or import changes.
oferchen added a commit that referenced this pull request May 1, 2026
…3488)

* docs(fast_io): design session-level io_uring ring pool (#1409) (#3444)

* docs(fast_io): audit io_uring SQPOLL and DEFER_TASKRUN for socket I/O (#1267) (#3445)

* docs(ci): audit Windows ACL/xattr CI matrix gaps (#1869) (#3446)

* docs(fast_io): audit MADV_WILLNEED prefault for mmap'd basis files (#1662) (#3447)

* docs(batch): investigate zstd as batch-compatible compression alternative (#1685) (#3448)

* docs(fast_io): document mmap page-fault impact on io_uring SQPOLL (#1661) (#3449)

* docs: audit --delete-during ordering vs upstream rsync 3.4.1 (#3453)

Captures the audit findings from #1893 in
docs/architecture/delete-during.md and lays the groundwork for the
documentation work tracked in #1894. Contrasts upstream's per-directory
interleaved deletion (generator.c::recv_generator + delete_in_dir)
against oc-rsync's batched pre-transfer sweep
(crates/transfer/src/receiver/transfer.rs:532), enumerates the resulting
differences in phase ordering, determinism, filter evaluation, and error
semantics, and lists the follow-up actions: CHANGELOG / man-page note,
interop test for concurrent new+deleted entries, .rsync-filter
investigation, and a possible --delete-strict-order opt-in.

Refs #1893, #1894.

* feat: add --jump-host proxy-jump CLI flag (#3454)

Expose OpenSSH ProxyJump (-J) as --jump-host. Comma-separated
[user@]HOST[:PORT] hops are forwarded to the remote shell as
`ssh -J <value>` before the destination operand when the configured
remote shell is OpenSSH. Empty values are rejected at every layer.

Note: only the long form `--jump-host` is provided. Upstream rsync
3.4.1 binds `-J` to `--omit-link-times` (options.c:647), so reusing
the short flag would break wire compatibility.

Refs #1881

* docs: audit --iconv inert critical gap (#3455)

Document the parse-but-never-applied architectural dead-end where the
CLI accepts --iconv, validates and stores IconvSetting on ClientConfig,
and forwards the option to the remote peer over SSH, but the local
process never receives a FilenameConverter. ServerConfigBuilder::iconv()
exists with zero call sites; receiver and generator already pull a
converter from connection.iconv but always observe None.

Severity: critical. Filenames with non-ASCII bytes silently bypass
transcoding on every local-side path (file-list ingest, file-list emit,
filter matching, daemon module serving) when --iconv is supplied.

Companion to docs/audits/iconv-pipeline.md, narrowing on the single
missing IconvSetting -> FilenameConverter bridge that currently makes
every gap in that broader pipeline simultaneously unobservable.

Tracks tasks #1909, #1910, #1918. Remediation path enumerated against
existing #1911-#1919 task chain.

* fix: normalise Windows backslash to forward slash in wire-encoded paths (#3456)

A Windows oc-rsync sender that builds a `FileEntry` whose path was
constructed via `Path::join` / `PathBuf::push` (the normal case for
recursive transfers) emitted the native string with `\` separators
verbatim on the wire. A POSIX rsync receiver decoding those bytes
treated every `\` as part of a single filename, producing one literal
filename per source file instead of the expected directory hierarchy.

Upstream rsync 3.4.1 writes filename bytes verbatim in
`flist.c:send_file_entry()` (lines 534-570). The wire format remains
`/`-separated because every upstream build either runs on a POSIX
kernel or under Cygwin's POSIX layer, which presents `/`-separated
paths to the application before this code is reached. oc-rsync targets
native Win32 directly, so the sender must perform the separator
normalisation explicitly.

Before this fix on Windows:

    let mut path = PathBuf::from(\"subdir\");
    path.push(\"file.txt\");
    let entry = FileEntry::new_file(path, 1024, 0o644);
    entry.name_bytes() == b\"subdir\\\\file.txt\"   // wrong

After:

    entry.name_bytes() == b\"subdir/file.txt\"     // matches upstream

The fix introduces a single-purpose helper
`crates/protocol/src/flist/wire_path.rs::path_bytes_to_wire` that
mirrors the existing identity-on-Unix / convert-on-Windows pattern of
`wire_mode.rs`. The helper is applied at every wire-encode call site:

- `FileEntry::name_bytes()` (filename emission via `write_entry`)
- `write_symlink_target()` (symlink target emission)
- `strip_leading_slashes()` Windows branch trims both `/` and `\`

The `name_bytes()` accessor signature changes from `&[u8]` to
`Cow<'_, [u8]>` so the helper can borrow on Unix (zero allocation) and
own only when conversion is required on Windows. Sort comparators
borrow the inner slice via `Deref` and continue to work unchanged.

Tests added:
- `wire_path` module: 8 unit tests covering forward-slash identity,
  empty path, dot path, Unix borrow, Unix backslash preservation,
  Windows translation, mixed separators.
- `flist::write` regression tests: assert the wire-encoded filename
  contains no `\` byte and that a writer-then-reader roundtrip yields
  `subdir/file.txt` regardless of host platform.
- Symlink-target regression test asserting no `\` byte appears in the
  encoded target bytes.

Companion audit: docs/audits/windows-path.md cites upstream
flist.c:534-570 and util1.c:955-961.

Closes #1905
Refs #1939

* fix: validate IPv6 host with Ipv6Addr and support scoped zone ids (#3450)

* fix: validate IPv6 host with Ipv6Addr and support scoped zone ids

Closes #1879 and #1880.

The previous `host_contains_colon` heuristic in `SshCommand::target_argument`
treated any string containing `:` as IPv6 and wrapped it in brackets. That
silently accepted malformed input such as `2001:db8:::1` or `garbage:input`
and forwarded the unparseable literal to ssh.

Replace it with strict `Ipv6Addr::from_str` validation via a new
`parse_host_for_ssh` returning a `HostKind` enum (`Hostname` / `Ipv4` /
`Ipv6 { addr, zone }`). The parser also recognises RFC 4007 scoped zone
identifiers (e.g. `fe80::1%eth0`) and re-emits them inside the bracket
form (`[addr%zone]`) per upstream rsync convention. Zone ids are rejected
when empty or when they contain whitespace or `]`.

Before: `host_contains_colon("2001:db8:::1") == true` -> emits `[2001:db8:::1]`.
After:  `parse_host_for_ssh("2001:db8:::1")` returns `Err(InvalidIpv6)`, so
        the input is passed through unchanged and ssh surfaces the
        resolution failure instead of receiving a malformed bracketed
        literal.

Includes unit tests for: bare IPv4, bare hostname, bracketed IPv6, IPv6
with zone (`fe80::1%eth0` and `[fe80::1%en0]`), malformed multi-`::` IPv6,
zone with whitespace (rejected), and direct `parse_host_for_ssh`
classification across all `HostKind` and `BuildError` variants.

* style: apply cargo fmt to ssh ipv6 validation

* feat: add AppleDouble filter and optional xattr merge for macOS (#3457)

* feat: add AppleDouble filter for macOS sidecar exclusion (#1907)

Add the `--apple-double-skip` option which appends a perishable `._*`
exclusion to the filter chain. macOS writes AppleDouble sidecar files on
filesystems that cannot represent extended attributes natively (FAT,
exFAT, NFS, SMB) to carry FinderInfo, resource forks, and xattrs.
Replicating them across machines clutters destinations with stale
metadata.

The filter half of #1907 ships now. Upstream rsync 3.4.1 has no
equivalent flag, so the option uses the descriptive
`--apple-double-skip` name. The optional xattr merge half is deferred:
the existing `apple-fs` crate does not expose AppleDouble parsing or
xattr merging primitives, so a follow-up task will land that piece
alongside the required parser.

- New `filters::apple_double` module with the canonical `._*` pattern.
- `FilterSet::from_rules_with_apple_double` mirrors the
  `from_rules_with_cvs` convenience constructor.
- CLI plumbing through `ParsedArgs`, the command builder, the
  filter-rules collector, and the workflow runner.
- Integration tests under `crates/filters/tests/apple_double.rs`
  covering top-level/nested matching, perishable semantics, override
  precedence, and clear-rule interaction.
- Frontend tests cover argument parsing and an end-to-end transfer
  scenario that confirms `._foo` files are dropped while their parents
  copy through.
- Man page and `--help` text updated.

Refs #1907

* style: apply cargo fmt to apple-double filter

* refactor: use shell-words crate for ssh remote-shell parsing (#3451)

* refactor: use shell-words crate for ssh remote-shell parsing

Replace the bespoke byte-level state machine in `parse_remote_shell`
with `shell_words::split`, the well-supported POSIX shell tokenizer.

- Tokenization is delegated to the `shell-words` crate (1.1).
- The wrapper retains the three behaviours callers rely on:
  empty/whitespace input -> `Empty`, interior NUL -> `InteriorNull`,
  non-UTF-8 input -> `InvalidEncoding`.
- The historical `UnterminatedEscape`/`UnterminatedSingleQuote`/
  `UnterminatedDoubleQuote` variants collapse into a single
  `Parse(String)` variant carrying the `shell_words::ParseError`
  description. No external code matched on the removed variants.
- Adds a property test corpus (`crates/rsync_io/tests/parse_remote_shell.rs`)
  asserting parity with `shell_words::split` over arbitrary
  RSYNC_RSH-style inputs, plus explicit unit tests for the historical
  behaviours (quoting, escapes, whitespace, NUL byte, invalid Unicode).

Tasks: #1877, #1878.

* style: apply cargo fmt to ssh shell-words tokenizer tests

* chore: update Cargo.lock for shell-words dependency

Cargo.lock was not updated when shell-words = "1.1" was added to
crates/rsync_io/Cargo.toml in cc01bbc, causing the MSRV 1.88
workflow to fail with --locked.

* fix(ssh): reject trailing backslash escape in remote-shell tokenizer

shell_words::split silently accepts a dangling trailing backslash, but
upstream rsync (and the previous bespoke tokenizer) reject it. Add a
small validator that walks the string tracking single- and double-quote
regions so that backslashes inside single quotes are not flagged, and
returns true only when the input ends with an unescaped backslash that
has no character to escape.

This restores the test parser_rejects_trailing_escape that fails on the
shell-words crate alone.

* test: allow stricter Parse rejection vs shell_words in parity property

The bespoke remote-shell tokenizer rejects dangling trailing backslashes,
matching upstream rsync's `tokens = parse_arguments(...)`. The new
shell-words-based wrapper preserves that strictness via has_trailing_escape,
but `shell_words::split` silently absorbs the trailing backslash and returns
Ok. The parity property test was therefore failing on inputs ending in a
bare `\\` because parse_remote_shell returned Err(Parse) while shell_words
returned Ok.

The wrapper is intentionally a tightening, not a parity match in both
directions. Add an explicit (Err(Parse), Ok(_)) arm so the property test
encodes the contract: we may reject inputs shell_words accepts, but never
the other way around.

* chore: disable coverage workflow on push/pull_request (#3460)

Nightly llvm-cov 22.1 SIGSEGVs deterministically inside
llvm::coverage::CoverageMapping::getInstantiationGroups, breaking
both master and PR runs. Restrict the workflow to manual
workflow_dispatch until a known-good nightly is pinned via
RUSTUP_TOOLCHAIN.

* fix: avoid mmap basis when paired with io_uring writer (#3459)

* fix: avoid mmap basis when paired with io_uring writer

DeltaApplicator opened its basis file via MapFile::open_adaptive, which
selects mmap for files >= 1 MiB on Unix. The applicator has no
production caller today, but is the obvious next target for an
io_uring-output rewrite. Wiring an IoUringWriter to the applicator
without changing the basis path would submit mmap-backed pointers to
io_uring SQEs on block-ref copies >= the writer batch threshold,
exposing two failure modes:

1. Cold-page faults on the basis file are serviced under the SQE
   submission thread (worse, the SQPOLL kernel thread when SQPOLL is
   enabled), turning a "free" zero-copy write into a synchronous fault
   and stalling other in-flight SQEs on the same poller.
2. Concurrent truncation of the basis file raises SIGBUS while the
   kernel is dereferencing the page on our behalf - recovery from
   in-kernel SIGBUS is not signal-safe.

Upstream rsync 3.4.1 deliberately avoids mmap(2) for basis files for
the same truncation reason (fileio.c:214-217). Our BufferedMap matches
that decision.

Closes the F1 hazard from docs/audits/mmap-iouring-co-usage.md (#1660)
by introducing BasisWriterKind in DeltaApplyConfig: when the writer is
io_uring-backed, DeltaApplicator::new opens the basis via the new
MapFile::open_adaptive_buffered (forces AdaptiveMapStrategy::Buffered
regardless of size). Standard / std-write writers retain the existing
adaptive selection. Non-Unix is unaffected since BufferedMap is the
only basis strategy there.

Tests cover both directions: io_uring writer + 2 MiB basis stays on
BufferedMap, standard writer + 2 MiB basis still picks mmap on Unix.
docs/design/basis-file-io-policy.md updated with implementation status
noting that the io_uring-pairing axis is now wired; remaining hazard
columns (--inplace, --append, --copy-devices, sparse, network FS) are
future work tracked in the same doc.

Refs: #1906 (this task), #1660 (audit).

* fix: drop redundant Write import in applicator tests

The test module brings in `Write` via `use super::*;` which re-exports
the file-level `use std::io::{self, Read, Write};`. The explicit
`use std::io::Write as _;` is therefore unused and trips clippy under
`-D warnings`.

* feat: bridge IconvSetting to FilenameConverter (#3458)

Adds IconvSetting::resolve_converter() to map the CLI-side iconv
setting onto a transfer-side FilenameConverter, and wires the
converter through apply_common_server_flags so every SSH and daemon
ServerConfig builder populates ConnectionConfig.iconv when --iconv
is in effect. Without this bridge, the CLI parsed --iconv, validated
it, forwarded it to the remote peer over SSH, but the local file-list
reader and writer hooks always observed None and silently passed raw
bytes through.

Also rejects --iconv=LOCAL,REMOTE with a hard error when the iconv
cargo feature is compiled out, rather than silently no-opping.

Closes #1911
Closes #1915

* perf: wire IoUringDiskBatch into disk_commit hot path (#3452)

* perf: wire IoUringDiskBatch into disk_commit hot path

Task #1901. The disk-commit thread previously created an IoUringDiskBatch
via try_create_disk_batch() but bound it to `_disk_batch`, leaving every
write to fall through to the buffered path (thread.rs:127). All disk
writes therefore bypassed io_uring batching even when the policy was Auto
or Enabled on Linux 5.6+.

Introduce a Writer enum in disk_commit/writer.rs that dispatches between
ReusableBufWriter (existing 256 KB buffered path) and a new IoUring
variant that borrows the disk thread's persistent IoUringDiskBatch. The
IoUring variant is cfg-gated to all(target_os = "linux", feature =
"io_uring") so non-Linux builds never reference it.

In disk_commit/thread.rs, drop the underscore from the batch binding and
thread `disk_batch.as_mut()` into both process_file and process_whole_file
on every iteration of the message loop. The batch is created once per
thread and reused across all files via begin_file/commit_file.

In disk_commit/process.rs, replace the unconditional ReusableBufWriter
construction with a make_writer() helper that registers the file with
the batch when (a) the batch is present and (b) sparse mode is disabled.
Sparse writes require Seek, which IoUringDiskBatch does not implement,
so sparse mode keeps using the buffered writer via buffered_for_sparse().

Semantics preserved:
- Temp-file commit ordering: Writer::finish() calls commit_file(do_fsync)
  which flushes + fsyncs + detaches the file before commit_file() runs
  the rename. Buffered path drops the writer (closing the file) before
  rename, identical to prior behaviour.
- fsync: do_fsync flag flows through Writer::flush_and_sync (buffered)
  and Writer::finish (io_uring). The io_uring path makes flush_and_sync
  a no-op so commit_file performs both atomically in a single SQE.
- Error propagation: io::Result is preserved end-to-end with file_path
  context attached on fsync/commit errors.

* fix: gate unused Writer::finish parameters on non-Linux builds

The do_fsync and file_path parameters on Writer::finish are only
consumed by the io_uring arm. On non-Linux (or with the io_uring
feature disabled) the Buffered arm ignores them, which under
-D warnings escalates to a build failure.

* fix(disk_commit): force buffered writer for append mode

The IoUringDiskBatch writes via SQEs with absolute offsets starting at 0,
ignoring the file position set by `file.seek(append_offset)` in
open_output_file. This caused --append-mode transfers under io_uring to
overwrite the existing file prefix with zeros, surfacing as the
standalone:append interop test failing with NUL-byte corruption.

Gate Writer::IoUring off whenever begin.append_offset > 0 and route those
transfers through ReusableBufWriter, which honors the seek via standard
Write::write_all.

upstream: receiver.c:307-308 - file position is the source of truth in
append mode; any writer that ignores it cannot be used.

* docs(compress): convert restating comments to rustdoc in lz4 (#2026) (#3462)

Remove inline comments inside lz4 codec function bodies and tests
that simply echo the next statement. All public-item rustdoc and
upstream rsync references (token.c) remain intact.

* fix(filters): propagate P (protect) filter modifier in sender-side filter exchange (#3463)

oc-rsync was emitting `P pattern` directly on the wire while also
attaching the `r` (receiver-side) modifier derived from the rule's
`applies_to_receiver` flag. Upstream rsync rejects `Pr` because the
`P` prefix already specifies the side and `r` after a side-specifying
prefix triggers the "invalid modifier" error in exclude.c:1270-1271.

Upstream's `get_rule_prefix()` (exclude.c:1536-1572) only ever emits
`+`, `-`, or `:` as the leading character; `P` and `R` exist only as
parser sugar that lower to plain include/exclude rules carrying the
`FILTRULE_RECEIVER_SIDE` flag. The wire encoding for a P rule is
`-r pattern`; the wire encoding for an R rule is `+r pattern`.

Normalize Protect/Risk in `build_modern_prefix` so the wire stream
matches upstream byte-for-byte. The receiver-side flag is forced when
serializing Protect/Risk rule types so that hand-built
`FilterRuleWireFormat` values without `receiver_side=true` still
serialize correctly.

Reproduced and verified the fix against upstream rsync 3.4.1 daemon
in the rsync-profile podman container with
`--filter='P *.log'` push: protected files now survive `--delete`.

Removes `standalone:delete-filter-protect` from KNOWN_FAILURES and
DASHBOARD_ENTRIES.

upstream: exclude.c:1536-1542
upstream: exclude.c:1569-1572
upstream: exclude.c:1201-1206

* docs(checksums): convert restating comments to rustdoc in rolling (#2018) (#3461)

Cleans up the `crates/checksums/src/rolling/` test modules:

- Drop decorative banner divider in front of the golden-tests block; replace with a
  short paragraph that describes intent and references upstream checksum.c.
- Remove restating-the-code comments (e.g. "Verify it matches manual computation",
  "Verify rolling produces correct checksum after shift") whose information is
  already conveyed by the surrounding code or test name.
- Sharpen wire-format comments to call out their connection to upstream rsync's
  packed (s2 << 16) | s1 layout.

Production source files in `rolling/` already use proper rustdoc on every public
item, so no `///` conversions are required there. SAFETY comments and SIMD
weight-table explanations are preserved verbatim. No runtime behaviour changes.

* fix(checksums): apply checksum_seed to MD4 strong checksum (upstream parity) (#3465)

Upstream rsync's `get_checksum2()` (checksum.c:358-396) appends the negotiated
`checksum_seed` after the data when computing MD4 block strong sums:

    memcpy(buf1, buf, len);
    if (checksum_seed) {
        SIVAL(buf1, len, checksum_seed);
        len += 4;
    }

Our MD4 path was unconditionally calling `Md4::digest(data)` and ignoring the
seed, so block-level strong checksums diverged from upstream whenever the
session negotiated a non-zero seed. This silently hurt delta-transfer match
quality across rsync<->oc-rsync interop and inflated `hash_hits` /
`false_alarms` counters in delta-stats output.

Changes:

* Add `Md4::digest_with_seed(seed, data)` mirroring upstream's append-seed-
  after-data semantics. A zero seed is a no-op (matches upstream's
  `if (checksum_seed)` guard).
* Add `SignatureAlgorithm::Md4Seeded { seed }` variant. Introducing a new
  variant rather than mutating the unit `Md4` keeps the 30+ existing
  call-sites that match on `Md4` working.
* `ChecksumFactory::signature_algorithm()` now selects `Md4Seeded` when MD4
  (or the legacy `None`/protocol<27 default) runs with a non-zero seed, and
  keeps unit `Md4` for the seed=0 case so existing wire goldens stay byte-
  identical.
* Extend exhaustive matches in `signature::algorithm`, the parallel
  checksum executor, and the delta-transfer bench to cover `Md4Seeded`.

Tests:

* `md4_seeded_appends_seed_after_data` - verifies the byte layout matches
  building `(data || seed_le_bytes)` and hashing with plain MD4.
* `md4_seeded_zero_seed_matches_unseeded` - guards the upstream zero-seed
  short-circuit.
* `md4_seeded_negative_seed_is_le_two_complement` - confirms i32 wire
  encoding for negative seeds.
* `md4_seeded_signature_matches_upstream_format` - parity at the
  `SignatureAlgorithm` layer.
* Three `ChecksumFactory` tests covering MD4/None x seed=0/non-zero.

upstream: checksum.c:358-396 `get_checksum2()` MD4 branch

* fix(filters): correct R-before-P ordering in delete-filter-risk interop test (#3464)

* fix(filters): correct R-before-P ordering in delete-filter-risk interop test

The standalone:delete-filter-risk interop test had the filter rules in the
wrong order: --filter='P *.log' --filter='P *.sh' --filter='R *.log'.

Upstream rsync evaluates filter rules first-match-wins (exclude.c:1038-1065
check_filter()). For R (risk) to override P (protect) on *.log, it must be
listed BEFORE the P rule. With R last, the P rule matched first and the
*.log files were never deleted.

Verified that upstream rsync 3.4.1 itself produces the same "wrong"
outcome with the original P-first ordering, confirming the test
expectation - not the filter engine - was incorrect. oc-rsync's filter
engine already mirrors upstream semantics; the unit test
risk_rule_allows_deletion_before_protection in crates/filters/src/tests.rs
explicitly documents the required R-before-P order.

Reordered both directions (up->oc and oc->up) to use
--filter='R *.log' --filter='P *.log' --filter='P *.sh' and updated the
function-level comment to cite exclude.c:1201-1207 (R rflags) and
exclude.c:1038-1065 (first-match-wins). Verified end-to-end in the
rsync-profile container that both upstream->oc and oc->upstream daemon
pushes now produce the expected outcome:
  - source files transferred
  - risky.log + subdir/nested.log deleted (R overrides P)
  - keeper.sh preserved (P with no preceding R)
  - destonly.txt deleted (no protection)

Removed the entry from KNOWN_FAILURES and DASHBOARD_ENTRIES in
tools/ci/known_failures.conf.

upstream: exclude.c:1201-1207 'R' = FILTRULE_INCLUDE|FILTRULE_RECEIVER_SIDE
upstream: exclude.c:1038-1065 check_filter() first-match-wins

* fix(filters): suppress redundant r/s modifier on Risk/Protect wire prefix

The wire encoder unconditionally emitted `s`/`r` modifiers when the
sender_side/receiver_side flags were set on a FilterRuleWireFormat.
This produced output like `Rr *.log` for a Risk rule (which oc-rsync
internally tags as receiver-side). Upstream rsync's parser rejects
that with `invalid modifier 'r' at position 1 in filter rule`,
breaking the delete-filter-risk interop scenario in oc->upstream
direction with exit 12.

Upstream's filter parser (exclude.c:1180-1207) sets
prefix_specifies_side when the rule type char is R/P (and S/H), and
exclude.c:1269-1278 rejects an explicit `r`/`s` modifier in that case.
Match upstream's get_rule_prefix (exclude.c:1525-1587), which never
emits the redundant flag for those prefixes.

Suppress `s`/`r` emission when the rule type is Risk or Protect.
Add unit tests at the prefix builder level and wire-level tests
including a Risk roundtrip to lock in the format.

* docs(protocol): convert restating comments to rustdoc in varint (#1999) (#3466)

Remove decorative banner comments from the varint test module and
tighten internal comments in `read_varlong` to delete pure restatement
while preserving upstream rsync C source references (`io.c:read_varlong`,
`memcpy(u.b, b2+1, min_bytes-1)`).

No behaviour, signature, or import changes.

* docs(compress): convert restating comments to rustdoc in zlib (#2029) (#3467)

Remove decorative and restating-the-code comments from the zlib
module's tests, while preserving every upstream rsync C source
reference and comments that explain non-obvious test design
rationale. Non-test files (decoder.rs, encoder.rs, helpers.rs,
level.rs, mod.rs) already use proper rustdoc and required no
changes.

* docs: clean up comments in core::timeout (#2014) (#3471)

* docs(signature): convert restating comments to rustdoc (#2034) (#3474)

Drops inline comments that merely echo the immediately following code in
block_size.rs, pipelined_gen.rs, and async_gen.rs. Reworks the few that
remain to focus on the WHY (upstream-derived phase 2 short-circuit, sqrt
bound derivation, BATCH_SIZE cross-file consistency, disk I/O thread cap).
Comment-only change with no functional impact.

* docs(metadata): convert restating comments to rustdoc in chmod (#2022) (#3473)

Remove section-banner comments and pure-restatement comments from
chmod test modules. Convert a stranded `///` doc-comment in
`upstream_compatibility` to a proper `//!` module doc. Preserve all
comments that reference upstream rsync semantics or that explain the
non-obvious conditional-X / assign-empty-perms / octal-validation
rules. No functional code changes.

* feat(ci): add upstream rsync testsuite harness (#3470)

Adds tools/ci/run_upstream_testsuite.sh, which runs upstream rsync's
testsuite/*.test scripts against oc-rsync. Mirrors upstream's
runtests.sh contract: exports $RSYNC, $TOOLDIR, $srcdir, $suitedir,
$scratchdir, $TLS_ARGS, $POSIXLY_CORRECT, and $ECHO_* per test.

Difference vs upstream runtests.sh: $RSYNC points at oc-rsync, not
upstream. Upstream sources are still needed for helper tools (tls,
getgroups, lsh.sh) and config artefacts (config.h, shconfig); the
harness fetches and configures them on first run.

Known failures live in tools/ci/upstream_testsuite_known_failures.conf
and are grouped by category (lsh.sh-routed remote-shell tests,
daemon-mode tests, ACL/xattr, devices, chown, hardlinks INC_RECURSE,
atimes/crtimes, etc). Tests in this list are reported XFAIL on failure
and UPASS on unexpected success so the list stays self-curating.

Wires up risk area #4 from the audit: protocol edge-case compatibility
against upstream's own conformance suite.

Usage:
  tools/ci/run_upstream_testsuite.sh           # all tests
  WHICHTESTS=00-hello.test tools/ci/...        # one test
  PRESERVE_SCRATCH=yes tools/ci/...            # keep per-test dirs

* docs: clean up comments in protocol::error_recovery (#1985) (#3472)

Remove restatement and decorative banner comments that echo the code
without adding value. Replace two banner-style remarks with focused
notes that explain non-obvious behavior (over-receive handling, why
HashMap re-insert is the desired semantic, the conservative default
classification, and the resume-vs-retry policy on transient errors).

Scope is limited to crates/protocol/src/error_recovery/. No functional
changes; tests and public APIs are unchanged.

Refs #1985

* docs(checksums): convert restating comments to rustdoc in strong (#2020) (#3469)

Audit of `crates/checksums/src/strong/` (excluding `strategy/`,
`md4_tests.rs`, `xxh64_tests.rs` per task scope). Production source files
are already well-documented from prior cleanup passes: every public type,
trait, function, and method carries rustdoc; upstream rsync references
(`upstream: checksum.c:get_checksum2()` and similar) are preserved on the
seed-handling paths in `md4.rs` and `md5.rs`; no decorative banners,
debug checkpoints, or commented-out code remain in scope.

The single substantive change in this pass adds a quirk comment to the
private `detect()` helper in `openssl_support.rs` that captures
non-obvious upstream behaviour: MD4 may be absent on OpenSSL builds
without the legacy provider, so the MD4 probe is best-effort and overall
detection succeeds as long as MD5 works. This explains the
otherwise-mysterious `if let Some(md4) = ...` whose result is
deliberately discarded.

No behaviour, signature, or import changes.

* docs(compress): convert restating comments to rustdoc in strategy (#2028) (#3468)

Remove decorative banner/divider comments from the compress::strategy
module. The module's rustdoc was already comprehensive; this cleanup
removes the remaining `// ---- Section ----` test-grouping banners
that violate the no-decorative-divider rule from CLAUDE.md.

All upstream rsync C source references and load-bearing internal
comments are preserved verbatim. No production code, function bodies,
signatures, types, or imports were modified.

* docs: add v0.6 known limitations and security hardening notes

Adds a "Known Limitations / Architectural Trade-offs" section to README.md
covering PBUF_RING 5.19+ requirement, io_uring buffer pool ceiling, SSH
double-compression interaction, single-thread delta computation, daemon TLS
gap, and Windows IOCP wiring status (#1868).

Updates SECURITY.md supported-versions table to 0.6.x and adds a "Hardening
Notes" section covering recycle_buffer release-mode bounds-check gap, bgid
u16 namespace exhaustion, SSH double-compression amplification surface,
daemon TLS-in-front guidance (stunnel / SSH tunnel / reverse proxy), and
daemon module hardening defaults.

Cross-links the two documents so operators planning a deployment have a
single source of truth for the documented trade-offs.

* docs: comment cleanup in protocol::flist::hardlink

Remove restating-the-code comments from the hardlink test suite and
fix two malformed upstream references in types.rs that used `// upstream:`
inside rustdoc blocks (rendered literally in generated docs).

Preserved: all upstream rsync source references, non-obvious WHY
explanations (FxHash collision rationale, swapped-value asymmetry,
weak-mixing input categorisation), and module-level documentation.

* docs(filters): audit .rsync-filter per-directory inheritance (#2050)

Compare oc-rsync's per-directory merge file inheritance against
upstream rsync 3.4.1. Documents the push/pop lifecycle, modifier
semantics (n, e, p, s, r, !), and parent-dirscan behaviour. Identifies
three behavioural bugs in FilterChain (n modifier ignored, !/clear
not propagated to scopes, include-only scopes cannot override outer
excludes), one intentional divergence (parent_dirscan), and one
untested area (nested dir-merge declarations).
oferchen added a commit that referenced this pull request May 1, 2026
* docs(fast_io): design session-level io_uring ring pool (#1409) (#3444)

* docs(fast_io): audit io_uring SQPOLL and DEFER_TASKRUN for socket I/O (#1267) (#3445)

* docs(ci): audit Windows ACL/xattr CI matrix gaps (#1869) (#3446)

* docs(fast_io): audit MADV_WILLNEED prefault for mmap'd basis files (#1662) (#3447)

* docs(batch): investigate zstd as batch-compatible compression alternative (#1685) (#3448)

* docs(fast_io): document mmap page-fault impact on io_uring SQPOLL (#1661) (#3449)

* docs: audit --delete-during ordering vs upstream rsync 3.4.1 (#3453)

Captures the audit findings from #1893 in
docs/architecture/delete-during.md and lays the groundwork for the
documentation work tracked in #1894. Contrasts upstream's per-directory
interleaved deletion (generator.c::recv_generator + delete_in_dir)
against oc-rsync's batched pre-transfer sweep
(crates/transfer/src/receiver/transfer.rs:532), enumerates the resulting
differences in phase ordering, determinism, filter evaluation, and error
semantics, and lists the follow-up actions: CHANGELOG / man-page note,
interop test for concurrent new+deleted entries, .rsync-filter
investigation, and a possible --delete-strict-order opt-in.

Refs #1893, #1894.

* feat: add --jump-host proxy-jump CLI flag (#3454)

Expose OpenSSH ProxyJump (-J) as --jump-host. Comma-separated
[user@]HOST[:PORT] hops are forwarded to the remote shell as
`ssh -J <value>` before the destination operand when the configured
remote shell is OpenSSH. Empty values are rejected at every layer.

Note: only the long form `--jump-host` is provided. Upstream rsync
3.4.1 binds `-J` to `--omit-link-times` (options.c:647), so reusing
the short flag would break wire compatibility.

Refs #1881

* docs: audit --iconv inert critical gap (#3455)

Document the parse-but-never-applied architectural dead-end where the
CLI accepts --iconv, validates and stores IconvSetting on ClientConfig,
and forwards the option to the remote peer over SSH, but the local
process never receives a FilenameConverter. ServerConfigBuilder::iconv()
exists with zero call sites; receiver and generator already pull a
converter from connection.iconv but always observe None.

Severity: critical. Filenames with non-ASCII bytes silently bypass
transcoding on every local-side path (file-list ingest, file-list emit,
filter matching, daemon module serving) when --iconv is supplied.

Companion to docs/audits/iconv-pipeline.md, narrowing on the single
missing IconvSetting -> FilenameConverter bridge that currently makes
every gap in that broader pipeline simultaneously unobservable.

Tracks tasks #1909, #1910, #1918. Remediation path enumerated against
existing #1911-#1919 task chain.

* fix: normalise Windows backslash to forward slash in wire-encoded paths (#3456)

A Windows oc-rsync sender that builds a `FileEntry` whose path was
constructed via `Path::join` / `PathBuf::push` (the normal case for
recursive transfers) emitted the native string with `\` separators
verbatim on the wire. A POSIX rsync receiver decoding those bytes
treated every `\` as part of a single filename, producing one literal
filename per source file instead of the expected directory hierarchy.

Upstream rsync 3.4.1 writes filename bytes verbatim in
`flist.c:send_file_entry()` (lines 534-570). The wire format remains
`/`-separated because every upstream build either runs on a POSIX
kernel or under Cygwin's POSIX layer, which presents `/`-separated
paths to the application before this code is reached. oc-rsync targets
native Win32 directly, so the sender must perform the separator
normalisation explicitly.

Before this fix on Windows:

    let mut path = PathBuf::from(\"subdir\");
    path.push(\"file.txt\");
    let entry = FileEntry::new_file(path, 1024, 0o644);
    entry.name_bytes() == b\"subdir\\\\file.txt\"   // wrong

After:

    entry.name_bytes() == b\"subdir/file.txt\"     // matches upstream

The fix introduces a single-purpose helper
`crates/protocol/src/flist/wire_path.rs::path_bytes_to_wire` that
mirrors the existing identity-on-Unix / convert-on-Windows pattern of
`wire_mode.rs`. The helper is applied at every wire-encode call site:

- `FileEntry::name_bytes()` (filename emission via `write_entry`)
- `write_symlink_target()` (symlink target emission)
- `strip_leading_slashes()` Windows branch trims both `/` and `\`

The `name_bytes()` accessor signature changes from `&[u8]` to
`Cow<'_, [u8]>` so the helper can borrow on Unix (zero allocation) and
own only when conversion is required on Windows. Sort comparators
borrow the inner slice via `Deref` and continue to work unchanged.

Tests added:
- `wire_path` module: 8 unit tests covering forward-slash identity,
  empty path, dot path, Unix borrow, Unix backslash preservation,
  Windows translation, mixed separators.
- `flist::write` regression tests: assert the wire-encoded filename
  contains no `\` byte and that a writer-then-reader roundtrip yields
  `subdir/file.txt` regardless of host platform.
- Symlink-target regression test asserting no `\` byte appears in the
  encoded target bytes.

Companion audit: docs/audits/windows-path.md cites upstream
flist.c:534-570 and util1.c:955-961.

Closes #1905
Refs #1939

* fix: validate IPv6 host with Ipv6Addr and support scoped zone ids (#3450)

* fix: validate IPv6 host with Ipv6Addr and support scoped zone ids

Closes #1879 and #1880.

The previous `host_contains_colon` heuristic in `SshCommand::target_argument`
treated any string containing `:` as IPv6 and wrapped it in brackets. That
silently accepted malformed input such as `2001:db8:::1` or `garbage:input`
and forwarded the unparseable literal to ssh.

Replace it with strict `Ipv6Addr::from_str` validation via a new
`parse_host_for_ssh` returning a `HostKind` enum (`Hostname` / `Ipv4` /
`Ipv6 { addr, zone }`). The parser also recognises RFC 4007 scoped zone
identifiers (e.g. `fe80::1%eth0`) and re-emits them inside the bracket
form (`[addr%zone]`) per upstream rsync convention. Zone ids are rejected
when empty or when they contain whitespace or `]`.

Before: `host_contains_colon("2001:db8:::1") == true` -> emits `[2001:db8:::1]`.
After:  `parse_host_for_ssh("2001:db8:::1")` returns `Err(InvalidIpv6)`, so
        the input is passed through unchanged and ssh surfaces the
        resolution failure instead of receiving a malformed bracketed
        literal.

Includes unit tests for: bare IPv4, bare hostname, bracketed IPv6, IPv6
with zone (`fe80::1%eth0` and `[fe80::1%en0]`), malformed multi-`::` IPv6,
zone with whitespace (rejected), and direct `parse_host_for_ssh`
classification across all `HostKind` and `BuildError` variants.

* style: apply cargo fmt to ssh ipv6 validation

* feat: add AppleDouble filter and optional xattr merge for macOS (#3457)

* feat: add AppleDouble filter for macOS sidecar exclusion (#1907)

Add the `--apple-double-skip` option which appends a perishable `._*`
exclusion to the filter chain. macOS writes AppleDouble sidecar files on
filesystems that cannot represent extended attributes natively (FAT,
exFAT, NFS, SMB) to carry FinderInfo, resource forks, and xattrs.
Replicating them across machines clutters destinations with stale
metadata.

The filter half of #1907 ships now. Upstream rsync 3.4.1 has no
equivalent flag, so the option uses the descriptive
`--apple-double-skip` name. The optional xattr merge half is deferred:
the existing `apple-fs` crate does not expose AppleDouble parsing or
xattr merging primitives, so a follow-up task will land that piece
alongside the required parser.

- New `filters::apple_double` module with the canonical `._*` pattern.
- `FilterSet::from_rules_with_apple_double` mirrors the
  `from_rules_with_cvs` convenience constructor.
- CLI plumbing through `ParsedArgs`, the command builder, the
  filter-rules collector, and the workflow runner.
- Integration tests under `crates/filters/tests/apple_double.rs`
  covering top-level/nested matching, perishable semantics, override
  precedence, and clear-rule interaction.
- Frontend tests cover argument parsing and an end-to-end transfer
  scenario that confirms `._foo` files are dropped while their parents
  copy through.
- Man page and `--help` text updated.

Refs #1907

* style: apply cargo fmt to apple-double filter

* refactor: use shell-words crate for ssh remote-shell parsing (#3451)

* refactor: use shell-words crate for ssh remote-shell parsing

Replace the bespoke byte-level state machine in `parse_remote_shell`
with `shell_words::split`, the well-supported POSIX shell tokenizer.

- Tokenization is delegated to the `shell-words` crate (1.1).
- The wrapper retains the three behaviours callers rely on:
  empty/whitespace input -> `Empty`, interior NUL -> `InteriorNull`,
  non-UTF-8 input -> `InvalidEncoding`.
- The historical `UnterminatedEscape`/`UnterminatedSingleQuote`/
  `UnterminatedDoubleQuote` variants collapse into a single
  `Parse(String)` variant carrying the `shell_words::ParseError`
  description. No external code matched on the removed variants.
- Adds a property test corpus (`crates/rsync_io/tests/parse_remote_shell.rs`)
  asserting parity with `shell_words::split` over arbitrary
  RSYNC_RSH-style inputs, plus explicit unit tests for the historical
  behaviours (quoting, escapes, whitespace, NUL byte, invalid Unicode).

Tasks: #1877, #1878.

* style: apply cargo fmt to ssh shell-words tokenizer tests

* chore: update Cargo.lock for shell-words dependency

Cargo.lock was not updated when shell-words = "1.1" was added to
crates/rsync_io/Cargo.toml in cc01bbc, causing the MSRV 1.88
workflow to fail with --locked.

* fix(ssh): reject trailing backslash escape in remote-shell tokenizer

shell_words::split silently accepts a dangling trailing backslash, but
upstream rsync (and the previous bespoke tokenizer) reject it. Add a
small validator that walks the string tracking single- and double-quote
regions so that backslashes inside single quotes are not flagged, and
returns true only when the input ends with an unescaped backslash that
has no character to escape.

This restores the test parser_rejects_trailing_escape that fails on the
shell-words crate alone.

* test: allow stricter Parse rejection vs shell_words in parity property

The bespoke remote-shell tokenizer rejects dangling trailing backslashes,
matching upstream rsync's `tokens = parse_arguments(...)`. The new
shell-words-based wrapper preserves that strictness via has_trailing_escape,
but `shell_words::split` silently absorbs the trailing backslash and returns
Ok. The parity property test was therefore failing on inputs ending in a
bare `\\` because parse_remote_shell returned Err(Parse) while shell_words
returned Ok.

The wrapper is intentionally a tightening, not a parity match in both
directions. Add an explicit (Err(Parse), Ok(_)) arm so the property test
encodes the contract: we may reject inputs shell_words accepts, but never
the other way around.

* chore: disable coverage workflow on push/pull_request (#3460)

Nightly llvm-cov 22.1 SIGSEGVs deterministically inside
llvm::coverage::CoverageMapping::getInstantiationGroups, breaking
both master and PR runs. Restrict the workflow to manual
workflow_dispatch until a known-good nightly is pinned via
RUSTUP_TOOLCHAIN.

* fix: avoid mmap basis when paired with io_uring writer (#3459)

* fix: avoid mmap basis when paired with io_uring writer

DeltaApplicator opened its basis file via MapFile::open_adaptive, which
selects mmap for files >= 1 MiB on Unix. The applicator has no
production caller today, but is the obvious next target for an
io_uring-output rewrite. Wiring an IoUringWriter to the applicator
without changing the basis path would submit mmap-backed pointers to
io_uring SQEs on block-ref copies >= the writer batch threshold,
exposing two failure modes:

1. Cold-page faults on the basis file are serviced under the SQE
   submission thread (worse, the SQPOLL kernel thread when SQPOLL is
   enabled), turning a "free" zero-copy write into a synchronous fault
   and stalling other in-flight SQEs on the same poller.
2. Concurrent truncation of the basis file raises SIGBUS while the
   kernel is dereferencing the page on our behalf - recovery from
   in-kernel SIGBUS is not signal-safe.

Upstream rsync 3.4.1 deliberately avoids mmap(2) for basis files for
the same truncation reason (fileio.c:214-217). Our BufferedMap matches
that decision.

Closes the F1 hazard from docs/audits/mmap-iouring-co-usage.md (#1660)
by introducing BasisWriterKind in DeltaApplyConfig: when the writer is
io_uring-backed, DeltaApplicator::new opens the basis via the new
MapFile::open_adaptive_buffered (forces AdaptiveMapStrategy::Buffered
regardless of size). Standard / std-write writers retain the existing
adaptive selection. Non-Unix is unaffected since BufferedMap is the
only basis strategy there.

Tests cover both directions: io_uring writer + 2 MiB basis stays on
BufferedMap, standard writer + 2 MiB basis still picks mmap on Unix.
docs/design/basis-file-io-policy.md updated with implementation status
noting that the io_uring-pairing axis is now wired; remaining hazard
columns (--inplace, --append, --copy-devices, sparse, network FS) are
future work tracked in the same doc.

Refs: #1906 (this task), #1660 (audit).

* fix: drop redundant Write import in applicator tests

The test module brings in `Write` via `use super::*;` which re-exports
the file-level `use std::io::{self, Read, Write};`. The explicit
`use std::io::Write as _;` is therefore unused and trips clippy under
`-D warnings`.

* feat: bridge IconvSetting to FilenameConverter (#3458)

Adds IconvSetting::resolve_converter() to map the CLI-side iconv
setting onto a transfer-side FilenameConverter, and wires the
converter through apply_common_server_flags so every SSH and daemon
ServerConfig builder populates ConnectionConfig.iconv when --iconv
is in effect. Without this bridge, the CLI parsed --iconv, validated
it, forwarded it to the remote peer over SSH, but the local file-list
reader and writer hooks always observed None and silently passed raw
bytes through.

Also rejects --iconv=LOCAL,REMOTE with a hard error when the iconv
cargo feature is compiled out, rather than silently no-opping.

Closes #1911
Closes #1915

* perf: wire IoUringDiskBatch into disk_commit hot path (#3452)

* perf: wire IoUringDiskBatch into disk_commit hot path

Task #1901. The disk-commit thread previously created an IoUringDiskBatch
via try_create_disk_batch() but bound it to `_disk_batch`, leaving every
write to fall through to the buffered path (thread.rs:127). All disk
writes therefore bypassed io_uring batching even when the policy was Auto
or Enabled on Linux 5.6+.

Introduce a Writer enum in disk_commit/writer.rs that dispatches between
ReusableBufWriter (existing 256 KB buffered path) and a new IoUring
variant that borrows the disk thread's persistent IoUringDiskBatch. The
IoUring variant is cfg-gated to all(target_os = "linux", feature =
"io_uring") so non-Linux builds never reference it.

In disk_commit/thread.rs, drop the underscore from the batch binding and
thread `disk_batch.as_mut()` into both process_file and process_whole_file
on every iteration of the message loop. The batch is created once per
thread and reused across all files via begin_file/commit_file.

In disk_commit/process.rs, replace the unconditional ReusableBufWriter
construction with a make_writer() helper that registers the file with
the batch when (a) the batch is present and (b) sparse mode is disabled.
Sparse writes require Seek, which IoUringDiskBatch does not implement,
so sparse mode keeps using the buffered writer via buffered_for_sparse().

Semantics preserved:
- Temp-file commit ordering: Writer::finish() calls commit_file(do_fsync)
  which flushes + fsyncs + detaches the file before commit_file() runs
  the rename. Buffered path drops the writer (closing the file) before
  rename, identical to prior behaviour.
- fsync: do_fsync flag flows through Writer::flush_and_sync (buffered)
  and Writer::finish (io_uring). The io_uring path makes flush_and_sync
  a no-op so commit_file performs both atomically in a single SQE.
- Error propagation: io::Result is preserved end-to-end with file_path
  context attached on fsync/commit errors.

* fix: gate unused Writer::finish parameters on non-Linux builds

The do_fsync and file_path parameters on Writer::finish are only
consumed by the io_uring arm. On non-Linux (or with the io_uring
feature disabled) the Buffered arm ignores them, which under
-D warnings escalates to a build failure.

* fix(disk_commit): force buffered writer for append mode

The IoUringDiskBatch writes via SQEs with absolute offsets starting at 0,
ignoring the file position set by `file.seek(append_offset)` in
open_output_file. This caused --append-mode transfers under io_uring to
overwrite the existing file prefix with zeros, surfacing as the
standalone:append interop test failing with NUL-byte corruption.

Gate Writer::IoUring off whenever begin.append_offset > 0 and route those
transfers through ReusableBufWriter, which honors the seek via standard
Write::write_all.

upstream: receiver.c:307-308 - file position is the source of truth in
append mode; any writer that ignores it cannot be used.

* docs(compress): convert restating comments to rustdoc in lz4 (#2026) (#3462)

Remove inline comments inside lz4 codec function bodies and tests
that simply echo the next statement. All public-item rustdoc and
upstream rsync references (token.c) remain intact.

* fix(filters): propagate P (protect) filter modifier in sender-side filter exchange (#3463)

oc-rsync was emitting `P pattern` directly on the wire while also
attaching the `r` (receiver-side) modifier derived from the rule's
`applies_to_receiver` flag. Upstream rsync rejects `Pr` because the
`P` prefix already specifies the side and `r` after a side-specifying
prefix triggers the "invalid modifier" error in exclude.c:1270-1271.

Upstream's `get_rule_prefix()` (exclude.c:1536-1572) only ever emits
`+`, `-`, or `:` as the leading character; `P` and `R` exist only as
parser sugar that lower to plain include/exclude rules carrying the
`FILTRULE_RECEIVER_SIDE` flag. The wire encoding for a P rule is
`-r pattern`; the wire encoding for an R rule is `+r pattern`.

Normalize Protect/Risk in `build_modern_prefix` so the wire stream
matches upstream byte-for-byte. The receiver-side flag is forced when
serializing Protect/Risk rule types so that hand-built
`FilterRuleWireFormat` values without `receiver_side=true` still
serialize correctly.

Reproduced and verified the fix against upstream rsync 3.4.1 daemon
in the rsync-profile podman container with
`--filter='P *.log'` push: protected files now survive `--delete`.

Removes `standalone:delete-filter-protect` from KNOWN_FAILURES and
DASHBOARD_ENTRIES.

upstream: exclude.c:1536-1542
upstream: exclude.c:1569-1572
upstream: exclude.c:1201-1206

* docs(checksums): convert restating comments to rustdoc in rolling (#2018) (#3461)

Cleans up the `crates/checksums/src/rolling/` test modules:

- Drop decorative banner divider in front of the golden-tests block; replace with a
  short paragraph that describes intent and references upstream checksum.c.
- Remove restating-the-code comments (e.g. "Verify it matches manual computation",
  "Verify rolling produces correct checksum after shift") whose information is
  already conveyed by the surrounding code or test name.
- Sharpen wire-format comments to call out their connection to upstream rsync's
  packed (s2 << 16) | s1 layout.

Production source files in `rolling/` already use proper rustdoc on every public
item, so no `///` conversions are required there. SAFETY comments and SIMD
weight-table explanations are preserved verbatim. No runtime behaviour changes.

* fix(checksums): apply checksum_seed to MD4 strong checksum (upstream parity) (#3465)

Upstream rsync's `get_checksum2()` (checksum.c:358-396) appends the negotiated
`checksum_seed` after the data when computing MD4 block strong sums:

    memcpy(buf1, buf, len);
    if (checksum_seed) {
        SIVAL(buf1, len, checksum_seed);
        len += 4;
    }

Our MD4 path was unconditionally calling `Md4::digest(data)` and ignoring the
seed, so block-level strong checksums diverged from upstream whenever the
session negotiated a non-zero seed. This silently hurt delta-transfer match
quality across rsync<->oc-rsync interop and inflated `hash_hits` /
`false_alarms` counters in delta-stats output.

Changes:

* Add `Md4::digest_with_seed(seed, data)` mirroring upstream's append-seed-
  after-data semantics. A zero seed is a no-op (matches upstream's
  `if (checksum_seed)` guard).
* Add `SignatureAlgorithm::Md4Seeded { seed }` variant. Introducing a new
  variant rather than mutating the unit `Md4` keeps the 30+ existing
  call-sites that match on `Md4` working.
* `ChecksumFactory::signature_algorithm()` now selects `Md4Seeded` when MD4
  (or the legacy `None`/protocol<27 default) runs with a non-zero seed, and
  keeps unit `Md4` for the seed=0 case so existing wire goldens stay byte-
  identical.
* Extend exhaustive matches in `signature::algorithm`, the parallel
  checksum executor, and the delta-transfer bench to cover `Md4Seeded`.

Tests:

* `md4_seeded_appends_seed_after_data` - verifies the byte layout matches
  building `(data || seed_le_bytes)` and hashing with plain MD4.
* `md4_seeded_zero_seed_matches_unseeded` - guards the upstream zero-seed
  short-circuit.
* `md4_seeded_negative_seed_is_le_two_complement` - confirms i32 wire
  encoding for negative seeds.
* `md4_seeded_signature_matches_upstream_format` - parity at the
  `SignatureAlgorithm` layer.
* Three `ChecksumFactory` tests covering MD4/None x seed=0/non-zero.

upstream: checksum.c:358-396 `get_checksum2()` MD4 branch

* fix(filters): correct R-before-P ordering in delete-filter-risk interop test (#3464)

* fix(filters): correct R-before-P ordering in delete-filter-risk interop test

The standalone:delete-filter-risk interop test had the filter rules in the
wrong order: --filter='P *.log' --filter='P *.sh' --filter='R *.log'.

Upstream rsync evaluates filter rules first-match-wins (exclude.c:1038-1065
check_filter()). For R (risk) to override P (protect) on *.log, it must be
listed BEFORE the P rule. With R last, the P rule matched first and the
*.log files were never deleted.

Verified that upstream rsync 3.4.1 itself produces the same "wrong"
outcome with the original P-first ordering, confirming the test
expectation - not the filter engine - was incorrect. oc-rsync's filter
engine already mirrors upstream semantics; the unit test
risk_rule_allows_deletion_before_protection in crates/filters/src/tests.rs
explicitly documents the required R-before-P order.

Reordered both directions (up->oc and oc->up) to use
--filter='R *.log' --filter='P *.log' --filter='P *.sh' and updated the
function-level comment to cite exclude.c:1201-1207 (R rflags) and
exclude.c:1038-1065 (first-match-wins). Verified end-to-end in the
rsync-profile container that both upstream->oc and oc->upstream daemon
pushes now produce the expected outcome:
  - source files transferred
  - risky.log + subdir/nested.log deleted (R overrides P)
  - keeper.sh preserved (P with no preceding R)
  - destonly.txt deleted (no protection)

Removed the entry from KNOWN_FAILURES and DASHBOARD_ENTRIES in
tools/ci/known_failures.conf.

upstream: exclude.c:1201-1207 'R' = FILTRULE_INCLUDE|FILTRULE_RECEIVER_SIDE
upstream: exclude.c:1038-1065 check_filter() first-match-wins

* fix(filters): suppress redundant r/s modifier on Risk/Protect wire prefix

The wire encoder unconditionally emitted `s`/`r` modifiers when the
sender_side/receiver_side flags were set on a FilterRuleWireFormat.
This produced output like `Rr *.log` for a Risk rule (which oc-rsync
internally tags as receiver-side). Upstream rsync's parser rejects
that with `invalid modifier 'r' at position 1 in filter rule`,
breaking the delete-filter-risk interop scenario in oc->upstream
direction with exit 12.

Upstream's filter parser (exclude.c:1180-1207) sets
prefix_specifies_side when the rule type char is R/P (and S/H), and
exclude.c:1269-1278 rejects an explicit `r`/`s` modifier in that case.
Match upstream's get_rule_prefix (exclude.c:1525-1587), which never
emits the redundant flag for those prefixes.

Suppress `s`/`r` emission when the rule type is Risk or Protect.
Add unit tests at the prefix builder level and wire-level tests
including a Risk roundtrip to lock in the format.

* docs(protocol): convert restating comments to rustdoc in varint (#1999) (#3466)

Remove decorative banner comments from the varint test module and
tighten internal comments in `read_varlong` to delete pure restatement
while preserving upstream rsync C source references (`io.c:read_varlong`,
`memcpy(u.b, b2+1, min_bytes-1)`).

No behaviour, signature, or import changes.

* docs(compress): convert restating comments to rustdoc in zlib (#2029) (#3467)

Remove decorative and restating-the-code comments from the zlib
module's tests, while preserving every upstream rsync C source
reference and comments that explain non-obvious test design
rationale. Non-test files (decoder.rs, encoder.rs, helpers.rs,
level.rs, mod.rs) already use proper rustdoc and required no
changes.

* docs: clean up comments in core::timeout (#2014) (#3471)

* docs(signature): convert restating comments to rustdoc (#2034) (#3474)

Drops inline comments that merely echo the immediately following code in
block_size.rs, pipelined_gen.rs, and async_gen.rs. Reworks the few that
remain to focus on the WHY (upstream-derived phase 2 short-circuit, sqrt
bound derivation, BATCH_SIZE cross-file consistency, disk I/O thread cap).
Comment-only change with no functional impact.

* docs(metadata): convert restating comments to rustdoc in chmod (#2022) (#3473)

Remove section-banner comments and pure-restatement comments from
chmod test modules. Convert a stranded `///` doc-comment in
`upstream_compatibility` to a proper `//!` module doc. Preserve all
comments that reference upstream rsync semantics or that explain the
non-obvious conditional-X / assign-empty-perms / octal-validation
rules. No functional code changes.

* feat(ci): add upstream rsync testsuite harness (#3470)

Adds tools/ci/run_upstream_testsuite.sh, which runs upstream rsync's
testsuite/*.test scripts against oc-rsync. Mirrors upstream's
runtests.sh contract: exports $RSYNC, $TOOLDIR, $srcdir, $suitedir,
$scratchdir, $TLS_ARGS, $POSIXLY_CORRECT, and $ECHO_* per test.

Difference vs upstream runtests.sh: $RSYNC points at oc-rsync, not
upstream. Upstream sources are still needed for helper tools (tls,
getgroups, lsh.sh) and config artefacts (config.h, shconfig); the
harness fetches and configures them on first run.

Known failures live in tools/ci/upstream_testsuite_known_failures.conf
and are grouped by category (lsh.sh-routed remote-shell tests,
daemon-mode tests, ACL/xattr, devices, chown, hardlinks INC_RECURSE,
atimes/crtimes, etc). Tests in this list are reported XFAIL on failure
and UPASS on unexpected success so the list stays self-curating.

Wires up risk area #4 from the audit: protocol edge-case compatibility
against upstream's own conformance suite.

Usage:
  tools/ci/run_upstream_testsuite.sh           # all tests
  WHICHTESTS=00-hello.test tools/ci/...        # one test
  PRESERVE_SCRATCH=yes tools/ci/...            # keep per-test dirs

* docs: clean up comments in protocol::error_recovery (#1985) (#3472)

Remove restatement and decorative banner comments that echo the code
without adding value. Replace two banner-style remarks with focused
notes that explain non-obvious behavior (over-receive handling, why
HashMap re-insert is the desired semantic, the conservative default
classification, and the resume-vs-retry policy on transient errors).

Scope is limited to crates/protocol/src/error_recovery/. No functional
changes; tests and public APIs are unchanged.

Refs #1985

* docs(checksums): convert restating comments to rustdoc in strong (#2020) (#3469)

Audit of `crates/checksums/src/strong/` (excluding `strategy/`,
`md4_tests.rs`, `xxh64_tests.rs` per task scope). Production source files
are already well-documented from prior cleanup passes: every public type,
trait, function, and method carries rustdoc; upstream rsync references
(`upstream: checksum.c:get_checksum2()` and similar) are preserved on the
seed-handling paths in `md4.rs` and `md5.rs`; no decorative banners,
debug checkpoints, or commented-out code remain in scope.

The single substantive change in this pass adds a quirk comment to the
private `detect()` helper in `openssl_support.rs` that captures
non-obvious upstream behaviour: MD4 may be absent on OpenSSL builds
without the legacy provider, so the MD4 probe is best-effort and overall
detection succeeds as long as MD5 works. This explains the
otherwise-mysterious `if let Some(md4) = ...` whose result is
deliberately discarded.

No behaviour, signature, or import changes.

* docs(compress): convert restating comments to rustdoc in strategy (#2028) (#3468)

Remove decorative banner/divider comments from the compress::strategy
module. The module's rustdoc was already comprehensive; this cleanup
removes the remaining `// ---- Section ----` test-grouping banners
that violate the no-decorative-divider rule from CLAUDE.md.

All upstream rsync C source references and load-bearing internal
comments are preserved verbatim. No production code, function bodies,
signatures, types, or imports were modified.

* docs: add v0.6 known limitations and security hardening notes

Adds a "Known Limitations / Architectural Trade-offs" section to README.md
covering PBUF_RING 5.19+ requirement, io_uring buffer pool ceiling, SSH
double-compression interaction, single-thread delta computation, daemon TLS
gap, and Windows IOCP wiring status (#1868).

Updates SECURITY.md supported-versions table to 0.6.x and adds a "Hardening
Notes" section covering recycle_buffer release-mode bounds-check gap, bgid
u16 namespace exhaustion, SSH double-compression amplification surface,
daemon TLS-in-front guidance (stunnel / SSH tunnel / reverse proxy), and
daemon module hardening defaults.

Cross-links the two documents so operators planning a deployment have a
single source of truth for the documented trade-offs.

* docs: comment cleanup in protocol::flist::hardlink

Remove restating-the-code comments from the hardlink test suite and
fix two malformed upstream references in types.rs that used `// upstream:`
inside rustdoc blocks (rendered literally in generated docs).

Preserved: all upstream rsync source references, non-obvious WHY
explanations (FxHash collision rationale, swapped-value asymmetry,
weak-mixing input categorisation), and module-level documentation.

* docs(engine): audit --fuzzy basis-file search algorithm (#2051)

Document oc-rsync's --fuzzy / -y basis-file search and scoring
against upstream rsync 3.4.1 (generator.c::find_fuzzy() and
util1.c::fuzzy_distance()). Identifies six divergences (scoring
metric, phase A size+mtime short-circuit, FNAMECMP_FUZZY wire
emission, suffix heuristics, already-sent filtering, tie-breaker
direction) and three matches (-yy plumbing, --whole-file/--inplace
/--append interactions). Recommends Levenshtein-based scoring,
phase A short-circuit, and ITEM_BASIS_TYPE_FOLLOWS emission.
oferchen added a commit that referenced this pull request May 5, 2026
…3488)

* docs(fast_io): design session-level io_uring ring pool (#1409) (#3444)

* docs(fast_io): audit io_uring SQPOLL and DEFER_TASKRUN for socket I/O (#1267) (#3445)

* docs(ci): audit Windows ACL/xattr CI matrix gaps (#1869) (#3446)

* docs(fast_io): audit MADV_WILLNEED prefault for mmap'd basis files (#1662) (#3447)

* docs(batch): investigate zstd as batch-compatible compression alternative (#1685) (#3448)

* docs(fast_io): document mmap page-fault impact on io_uring SQPOLL (#1661) (#3449)

* docs: audit --delete-during ordering vs upstream rsync 3.4.1 (#3453)

Captures the audit findings from #1893 in
docs/architecture/delete-during.md and lays the groundwork for the
documentation work tracked in #1894. Contrasts upstream's per-directory
interleaved deletion (generator.c::recv_generator + delete_in_dir)
against oc-rsync's batched pre-transfer sweep
(crates/transfer/src/receiver/transfer.rs:532), enumerates the resulting
differences in phase ordering, determinism, filter evaluation, and error
semantics, and lists the follow-up actions: CHANGELOG / man-page note,
interop test for concurrent new+deleted entries, .rsync-filter
investigation, and a possible --delete-strict-order opt-in.

Refs #1893, #1894.

* feat: add --jump-host proxy-jump CLI flag (#3454)

Expose OpenSSH ProxyJump (-J) as --jump-host. Comma-separated
[user@]HOST[:PORT] hops are forwarded to the remote shell as
`ssh -J <value>` before the destination operand when the configured
remote shell is OpenSSH. Empty values are rejected at every layer.

Note: only the long form `--jump-host` is provided. Upstream rsync
3.4.1 binds `-J` to `--omit-link-times` (options.c:647), so reusing
the short flag would break wire compatibility.

Refs #1881

* docs: audit --iconv inert critical gap (#3455)

Document the parse-but-never-applied architectural dead-end where the
CLI accepts --iconv, validates and stores IconvSetting on ClientConfig,
and forwards the option to the remote peer over SSH, but the local
process never receives a FilenameConverter. ServerConfigBuilder::iconv()
exists with zero call sites; receiver and generator already pull a
converter from connection.iconv but always observe None.

Severity: critical. Filenames with non-ASCII bytes silently bypass
transcoding on every local-side path (file-list ingest, file-list emit,
filter matching, daemon module serving) when --iconv is supplied.

Companion to docs/audits/iconv-pipeline.md, narrowing on the single
missing IconvSetting -> FilenameConverter bridge that currently makes
every gap in that broader pipeline simultaneously unobservable.

Tracks tasks #1909, #1910, #1918. Remediation path enumerated against
existing #1911-#1919 task chain.

* fix: normalise Windows backslash to forward slash in wire-encoded paths (#3456)

A Windows oc-rsync sender that builds a `FileEntry` whose path was
constructed via `Path::join` / `PathBuf::push` (the normal case for
recursive transfers) emitted the native string with `\` separators
verbatim on the wire. A POSIX rsync receiver decoding those bytes
treated every `\` as part of a single filename, producing one literal
filename per source file instead of the expected directory hierarchy.

Upstream rsync 3.4.1 writes filename bytes verbatim in
`flist.c:send_file_entry()` (lines 534-570). The wire format remains
`/`-separated because every upstream build either runs on a POSIX
kernel or under Cygwin's POSIX layer, which presents `/`-separated
paths to the application before this code is reached. oc-rsync targets
native Win32 directly, so the sender must perform the separator
normalisation explicitly.

Before this fix on Windows:

    let mut path = PathBuf::from(\"subdir\");
    path.push(\"file.txt\");
    let entry = FileEntry::new_file(path, 1024, 0o644);
    entry.name_bytes() == b\"subdir\\\\file.txt\"   // wrong

After:

    entry.name_bytes() == b\"subdir/file.txt\"     // matches upstream

The fix introduces a single-purpose helper
`crates/protocol/src/flist/wire_path.rs::path_bytes_to_wire` that
mirrors the existing identity-on-Unix / convert-on-Windows pattern of
`wire_mode.rs`. The helper is applied at every wire-encode call site:

- `FileEntry::name_bytes()` (filename emission via `write_entry`)
- `write_symlink_target()` (symlink target emission)
- `strip_leading_slashes()` Windows branch trims both `/` and `\`

The `name_bytes()` accessor signature changes from `&[u8]` to
`Cow<'_, [u8]>` so the helper can borrow on Unix (zero allocation) and
own only when conversion is required on Windows. Sort comparators
borrow the inner slice via `Deref` and continue to work unchanged.

Tests added:
- `wire_path` module: 8 unit tests covering forward-slash identity,
  empty path, dot path, Unix borrow, Unix backslash preservation,
  Windows translation, mixed separators.
- `flist::write` regression tests: assert the wire-encoded filename
  contains no `\` byte and that a writer-then-reader roundtrip yields
  `subdir/file.txt` regardless of host platform.
- Symlink-target regression test asserting no `\` byte appears in the
  encoded target bytes.

Companion audit: docs/audits/windows-path.md cites upstream
flist.c:534-570 and util1.c:955-961.

Closes #1905
Refs #1939

* fix: validate IPv6 host with Ipv6Addr and support scoped zone ids (#3450)

* fix: validate IPv6 host with Ipv6Addr and support scoped zone ids

Closes #1879 and #1880.

The previous `host_contains_colon` heuristic in `SshCommand::target_argument`
treated any string containing `:` as IPv6 and wrapped it in brackets. That
silently accepted malformed input such as `2001:db8:::1` or `garbage:input`
and forwarded the unparseable literal to ssh.

Replace it with strict `Ipv6Addr::from_str` validation via a new
`parse_host_for_ssh` returning a `HostKind` enum (`Hostname` / `Ipv4` /
`Ipv6 { addr, zone }`). The parser also recognises RFC 4007 scoped zone
identifiers (e.g. `fe80::1%eth0`) and re-emits them inside the bracket
form (`[addr%zone]`) per upstream rsync convention. Zone ids are rejected
when empty or when they contain whitespace or `]`.

Before: `host_contains_colon("2001:db8:::1") == true` -> emits `[2001:db8:::1]`.
After:  `parse_host_for_ssh("2001:db8:::1")` returns `Err(InvalidIpv6)`, so
        the input is passed through unchanged and ssh surfaces the
        resolution failure instead of receiving a malformed bracketed
        literal.

Includes unit tests for: bare IPv4, bare hostname, bracketed IPv6, IPv6
with zone (`fe80::1%eth0` and `[fe80::1%en0]`), malformed multi-`::` IPv6,
zone with whitespace (rejected), and direct `parse_host_for_ssh`
classification across all `HostKind` and `BuildError` variants.

* style: apply cargo fmt to ssh ipv6 validation

* feat: add AppleDouble filter and optional xattr merge for macOS (#3457)

* feat: add AppleDouble filter for macOS sidecar exclusion (#1907)

Add the `--apple-double-skip` option which appends a perishable `._*`
exclusion to the filter chain. macOS writes AppleDouble sidecar files on
filesystems that cannot represent extended attributes natively (FAT,
exFAT, NFS, SMB) to carry FinderInfo, resource forks, and xattrs.
Replicating them across machines clutters destinations with stale
metadata.

The filter half of #1907 ships now. Upstream rsync 3.4.1 has no
equivalent flag, so the option uses the descriptive
`--apple-double-skip` name. The optional xattr merge half is deferred:
the existing `apple-fs` crate does not expose AppleDouble parsing or
xattr merging primitives, so a follow-up task will land that piece
alongside the required parser.

- New `filters::apple_double` module with the canonical `._*` pattern.
- `FilterSet::from_rules_with_apple_double` mirrors the
  `from_rules_with_cvs` convenience constructor.
- CLI plumbing through `ParsedArgs`, the command builder, the
  filter-rules collector, and the workflow runner.
- Integration tests under `crates/filters/tests/apple_double.rs`
  covering top-level/nested matching, perishable semantics, override
  precedence, and clear-rule interaction.
- Frontend tests cover argument parsing and an end-to-end transfer
  scenario that confirms `._foo` files are dropped while their parents
  copy through.
- Man page and `--help` text updated.

Refs #1907

* style: apply cargo fmt to apple-double filter

* refactor: use shell-words crate for ssh remote-shell parsing (#3451)

* refactor: use shell-words crate for ssh remote-shell parsing

Replace the bespoke byte-level state machine in `parse_remote_shell`
with `shell_words::split`, the well-supported POSIX shell tokenizer.

- Tokenization is delegated to the `shell-words` crate (1.1).
- The wrapper retains the three behaviours callers rely on:
  empty/whitespace input -> `Empty`, interior NUL -> `InteriorNull`,
  non-UTF-8 input -> `InvalidEncoding`.
- The historical `UnterminatedEscape`/`UnterminatedSingleQuote`/
  `UnterminatedDoubleQuote` variants collapse into a single
  `Parse(String)` variant carrying the `shell_words::ParseError`
  description. No external code matched on the removed variants.
- Adds a property test corpus (`crates/rsync_io/tests/parse_remote_shell.rs`)
  asserting parity with `shell_words::split` over arbitrary
  RSYNC_RSH-style inputs, plus explicit unit tests for the historical
  behaviours (quoting, escapes, whitespace, NUL byte, invalid Unicode).

Tasks: #1877, #1878.

* style: apply cargo fmt to ssh shell-words tokenizer tests

* chore: update Cargo.lock for shell-words dependency

Cargo.lock was not updated when shell-words = "1.1" was added to
crates/rsync_io/Cargo.toml in cc01bbc, causing the MSRV 1.88
workflow to fail with --locked.

* fix(ssh): reject trailing backslash escape in remote-shell tokenizer

shell_words::split silently accepts a dangling trailing backslash, but
upstream rsync (and the previous bespoke tokenizer) reject it. Add a
small validator that walks the string tracking single- and double-quote
regions so that backslashes inside single quotes are not flagged, and
returns true only when the input ends with an unescaped backslash that
has no character to escape.

This restores the test parser_rejects_trailing_escape that fails on the
shell-words crate alone.

* test: allow stricter Parse rejection vs shell_words in parity property

The bespoke remote-shell tokenizer rejects dangling trailing backslashes,
matching upstream rsync's `tokens = parse_arguments(...)`. The new
shell-words-based wrapper preserves that strictness via has_trailing_escape,
but `shell_words::split` silently absorbs the trailing backslash and returns
Ok. The parity property test was therefore failing on inputs ending in a
bare `\\` because parse_remote_shell returned Err(Parse) while shell_words
returned Ok.

The wrapper is intentionally a tightening, not a parity match in both
directions. Add an explicit (Err(Parse), Ok(_)) arm so the property test
encodes the contract: we may reject inputs shell_words accepts, but never
the other way around.

* chore: disable coverage workflow on push/pull_request (#3460)

Nightly llvm-cov 22.1 SIGSEGVs deterministically inside
llvm::coverage::CoverageMapping::getInstantiationGroups, breaking
both master and PR runs. Restrict the workflow to manual
workflow_dispatch until a known-good nightly is pinned via
RUSTUP_TOOLCHAIN.

* fix: avoid mmap basis when paired with io_uring writer (#3459)

* fix: avoid mmap basis when paired with io_uring writer

DeltaApplicator opened its basis file via MapFile::open_adaptive, which
selects mmap for files >= 1 MiB on Unix. The applicator has no
production caller today, but is the obvious next target for an
io_uring-output rewrite. Wiring an IoUringWriter to the applicator
without changing the basis path would submit mmap-backed pointers to
io_uring SQEs on block-ref copies >= the writer batch threshold,
exposing two failure modes:

1. Cold-page faults on the basis file are serviced under the SQE
   submission thread (worse, the SQPOLL kernel thread when SQPOLL is
   enabled), turning a "free" zero-copy write into a synchronous fault
   and stalling other in-flight SQEs on the same poller.
2. Concurrent truncation of the basis file raises SIGBUS while the
   kernel is dereferencing the page on our behalf - recovery from
   in-kernel SIGBUS is not signal-safe.

Upstream rsync 3.4.1 deliberately avoids mmap(2) for basis files for
the same truncation reason (fileio.c:214-217). Our BufferedMap matches
that decision.

Closes the F1 hazard from docs/audits/mmap-iouring-co-usage.md (#1660)
by introducing BasisWriterKind in DeltaApplyConfig: when the writer is
io_uring-backed, DeltaApplicator::new opens the basis via the new
MapFile::open_adaptive_buffered (forces AdaptiveMapStrategy::Buffered
regardless of size). Standard / std-write writers retain the existing
adaptive selection. Non-Unix is unaffected since BufferedMap is the
only basis strategy there.

Tests cover both directions: io_uring writer + 2 MiB basis stays on
BufferedMap, standard writer + 2 MiB basis still picks mmap on Unix.
docs/design/basis-file-io-policy.md updated with implementation status
noting that the io_uring-pairing axis is now wired; remaining hazard
columns (--inplace, --append, --copy-devices, sparse, network FS) are
future work tracked in the same doc.

Refs: #1906 (this task), #1660 (audit).

* fix: drop redundant Write import in applicator tests

The test module brings in `Write` via `use super::*;` which re-exports
the file-level `use std::io::{self, Read, Write};`. The explicit
`use std::io::Write as _;` is therefore unused and trips clippy under
`-D warnings`.

* feat: bridge IconvSetting to FilenameConverter (#3458)

Adds IconvSetting::resolve_converter() to map the CLI-side iconv
setting onto a transfer-side FilenameConverter, and wires the
converter through apply_common_server_flags so every SSH and daemon
ServerConfig builder populates ConnectionConfig.iconv when --iconv
is in effect. Without this bridge, the CLI parsed --iconv, validated
it, forwarded it to the remote peer over SSH, but the local file-list
reader and writer hooks always observed None and silently passed raw
bytes through.

Also rejects --iconv=LOCAL,REMOTE with a hard error when the iconv
cargo feature is compiled out, rather than silently no-opping.

Closes #1911
Closes #1915

* perf: wire IoUringDiskBatch into disk_commit hot path (#3452)

* perf: wire IoUringDiskBatch into disk_commit hot path

Task #1901. The disk-commit thread previously created an IoUringDiskBatch
via try_create_disk_batch() but bound it to `_disk_batch`, leaving every
write to fall through to the buffered path (thread.rs:127). All disk
writes therefore bypassed io_uring batching even when the policy was Auto
or Enabled on Linux 5.6+.

Introduce a Writer enum in disk_commit/writer.rs that dispatches between
ReusableBufWriter (existing 256 KB buffered path) and a new IoUring
variant that borrows the disk thread's persistent IoUringDiskBatch. The
IoUring variant is cfg-gated to all(target_os = "linux", feature =
"io_uring") so non-Linux builds never reference it.

In disk_commit/thread.rs, drop the underscore from the batch binding and
thread `disk_batch.as_mut()` into both process_file and process_whole_file
on every iteration of the message loop. The batch is created once per
thread and reused across all files via begin_file/commit_file.

In disk_commit/process.rs, replace the unconditional ReusableBufWriter
construction with a make_writer() helper that registers the file with
the batch when (a) the batch is present and (b) sparse mode is disabled.
Sparse writes require Seek, which IoUringDiskBatch does not implement,
so sparse mode keeps using the buffered writer via buffered_for_sparse().

Semantics preserved:
- Temp-file commit ordering: Writer::finish() calls commit_file(do_fsync)
  which flushes + fsyncs + detaches the file before commit_file() runs
  the rename. Buffered path drops the writer (closing the file) before
  rename, identical to prior behaviour.
- fsync: do_fsync flag flows through Writer::flush_and_sync (buffered)
  and Writer::finish (io_uring). The io_uring path makes flush_and_sync
  a no-op so commit_file performs both atomically in a single SQE.
- Error propagation: io::Result is preserved end-to-end with file_path
  context attached on fsync/commit errors.

* fix: gate unused Writer::finish parameters on non-Linux builds

The do_fsync and file_path parameters on Writer::finish are only
consumed by the io_uring arm. On non-Linux (or with the io_uring
feature disabled) the Buffered arm ignores them, which under
-D warnings escalates to a build failure.

* fix(disk_commit): force buffered writer for append mode

The IoUringDiskBatch writes via SQEs with absolute offsets starting at 0,
ignoring the file position set by `file.seek(append_offset)` in
open_output_file. This caused --append-mode transfers under io_uring to
overwrite the existing file prefix with zeros, surfacing as the
standalone:append interop test failing with NUL-byte corruption.

Gate Writer::IoUring off whenever begin.append_offset > 0 and route those
transfers through ReusableBufWriter, which honors the seek via standard
Write::write_all.

upstream: receiver.c:307-308 - file position is the source of truth in
append mode; any writer that ignores it cannot be used.

* docs(compress): convert restating comments to rustdoc in lz4 (#2026) (#3462)

Remove inline comments inside lz4 codec function bodies and tests
that simply echo the next statement. All public-item rustdoc and
upstream rsync references (token.c) remain intact.

* fix(filters): propagate P (protect) filter modifier in sender-side filter exchange (#3463)

oc-rsync was emitting `P pattern` directly on the wire while also
attaching the `r` (receiver-side) modifier derived from the rule's
`applies_to_receiver` flag. Upstream rsync rejects `Pr` because the
`P` prefix already specifies the side and `r` after a side-specifying
prefix triggers the "invalid modifier" error in exclude.c:1270-1271.

Upstream's `get_rule_prefix()` (exclude.c:1536-1572) only ever emits
`+`, `-`, or `:` as the leading character; `P` and `R` exist only as
parser sugar that lower to plain include/exclude rules carrying the
`FILTRULE_RECEIVER_SIDE` flag. The wire encoding for a P rule is
`-r pattern`; the wire encoding for an R rule is `+r pattern`.

Normalize Protect/Risk in `build_modern_prefix` so the wire stream
matches upstream byte-for-byte. The receiver-side flag is forced when
serializing Protect/Risk rule types so that hand-built
`FilterRuleWireFormat` values without `receiver_side=true` still
serialize correctly.

Reproduced and verified the fix against upstream rsync 3.4.1 daemon
in the rsync-profile podman container with
`--filter='P *.log'` push: protected files now survive `--delete`.

Removes `standalone:delete-filter-protect` from KNOWN_FAILURES and
DASHBOARD_ENTRIES.

upstream: exclude.c:1536-1542
upstream: exclude.c:1569-1572
upstream: exclude.c:1201-1206

* docs(checksums): convert restating comments to rustdoc in rolling (#2018) (#3461)

Cleans up the `crates/checksums/src/rolling/` test modules:

- Drop decorative banner divider in front of the golden-tests block; replace with a
  short paragraph that describes intent and references upstream checksum.c.
- Remove restating-the-code comments (e.g. "Verify it matches manual computation",
  "Verify rolling produces correct checksum after shift") whose information is
  already conveyed by the surrounding code or test name.
- Sharpen wire-format comments to call out their connection to upstream rsync's
  packed (s2 << 16) | s1 layout.

Production source files in `rolling/` already use proper rustdoc on every public
item, so no `///` conversions are required there. SAFETY comments and SIMD
weight-table explanations are preserved verbatim. No runtime behaviour changes.

* fix(checksums): apply checksum_seed to MD4 strong checksum (upstream parity) (#3465)

Upstream rsync's `get_checksum2()` (checksum.c:358-396) appends the negotiated
`checksum_seed` after the data when computing MD4 block strong sums:

    memcpy(buf1, buf, len);
    if (checksum_seed) {
        SIVAL(buf1, len, checksum_seed);
        len += 4;
    }

Our MD4 path was unconditionally calling `Md4::digest(data)` and ignoring the
seed, so block-level strong checksums diverged from upstream whenever the
session negotiated a non-zero seed. This silently hurt delta-transfer match
quality across rsync<->oc-rsync interop and inflated `hash_hits` /
`false_alarms` counters in delta-stats output.

Changes:

* Add `Md4::digest_with_seed(seed, data)` mirroring upstream's append-seed-
  after-data semantics. A zero seed is a no-op (matches upstream's
  `if (checksum_seed)` guard).
* Add `SignatureAlgorithm::Md4Seeded { seed }` variant. Introducing a new
  variant rather than mutating the unit `Md4` keeps the 30+ existing
  call-sites that match on `Md4` working.
* `ChecksumFactory::signature_algorithm()` now selects `Md4Seeded` when MD4
  (or the legacy `None`/protocol<27 default) runs with a non-zero seed, and
  keeps unit `Md4` for the seed=0 case so existing wire goldens stay byte-
  identical.
* Extend exhaustive matches in `signature::algorithm`, the parallel
  checksum executor, and the delta-transfer bench to cover `Md4Seeded`.

Tests:

* `md4_seeded_appends_seed_after_data` - verifies the byte layout matches
  building `(data || seed_le_bytes)` and hashing with plain MD4.
* `md4_seeded_zero_seed_matches_unseeded` - guards the upstream zero-seed
  short-circuit.
* `md4_seeded_negative_seed_is_le_two_complement` - confirms i32 wire
  encoding for negative seeds.
* `md4_seeded_signature_matches_upstream_format` - parity at the
  `SignatureAlgorithm` layer.
* Three `ChecksumFactory` tests covering MD4/None x seed=0/non-zero.

upstream: checksum.c:358-396 `get_checksum2()` MD4 branch

* fix(filters): correct R-before-P ordering in delete-filter-risk interop test (#3464)

* fix(filters): correct R-before-P ordering in delete-filter-risk interop test

The standalone:delete-filter-risk interop test had the filter rules in the
wrong order: --filter='P *.log' --filter='P *.sh' --filter='R *.log'.

Upstream rsync evaluates filter rules first-match-wins (exclude.c:1038-1065
check_filter()). For R (risk) to override P (protect) on *.log, it must be
listed BEFORE the P rule. With R last, the P rule matched first and the
*.log files were never deleted.

Verified that upstream rsync 3.4.1 itself produces the same "wrong"
outcome with the original P-first ordering, confirming the test
expectation - not the filter engine - was incorrect. oc-rsync's filter
engine already mirrors upstream semantics; the unit test
risk_rule_allows_deletion_before_protection in crates/filters/src/tests.rs
explicitly documents the required R-before-P order.

Reordered both directions (up->oc and oc->up) to use
--filter='R *.log' --filter='P *.log' --filter='P *.sh' and updated the
function-level comment to cite exclude.c:1201-1207 (R rflags) and
exclude.c:1038-1065 (first-match-wins). Verified end-to-end in the
rsync-profile container that both upstream->oc and oc->upstream daemon
pushes now produce the expected outcome:
  - source files transferred
  - risky.log + subdir/nested.log deleted (R overrides P)
  - keeper.sh preserved (P with no preceding R)
  - destonly.txt deleted (no protection)

Removed the entry from KNOWN_FAILURES and DASHBOARD_ENTRIES in
tools/ci/known_failures.conf.

upstream: exclude.c:1201-1207 'R' = FILTRULE_INCLUDE|FILTRULE_RECEIVER_SIDE
upstream: exclude.c:1038-1065 check_filter() first-match-wins

* fix(filters): suppress redundant r/s modifier on Risk/Protect wire prefix

The wire encoder unconditionally emitted `s`/`r` modifiers when the
sender_side/receiver_side flags were set on a FilterRuleWireFormat.
This produced output like `Rr *.log` for a Risk rule (which oc-rsync
internally tags as receiver-side). Upstream rsync's parser rejects
that with `invalid modifier 'r' at position 1 in filter rule`,
breaking the delete-filter-risk interop scenario in oc->upstream
direction with exit 12.

Upstream's filter parser (exclude.c:1180-1207) sets
prefix_specifies_side when the rule type char is R/P (and S/H), and
exclude.c:1269-1278 rejects an explicit `r`/`s` modifier in that case.
Match upstream's get_rule_prefix (exclude.c:1525-1587), which never
emits the redundant flag for those prefixes.

Suppress `s`/`r` emission when the rule type is Risk or Protect.
Add unit tests at the prefix builder level and wire-level tests
including a Risk roundtrip to lock in the format.

* docs(protocol): convert restating comments to rustdoc in varint (#1999) (#3466)

Remove decorative banner comments from the varint test module and
tighten internal comments in `read_varlong` to delete pure restatement
while preserving upstream rsync C source references (`io.c:read_varlong`,
`memcpy(u.b, b2+1, min_bytes-1)`).

No behaviour, signature, or import changes.

* docs(compress): convert restating comments to rustdoc in zlib (#2029) (#3467)

Remove decorative and restating-the-code comments from the zlib
module's tests, while preserving every upstream rsync C source
reference and comments that explain non-obvious test design
rationale. Non-test files (decoder.rs, encoder.rs, helpers.rs,
level.rs, mod.rs) already use proper rustdoc and required no
changes.

* docs: clean up comments in core::timeout (#2014) (#3471)

* docs(signature): convert restating comments to rustdoc (#2034) (#3474)

Drops inline comments that merely echo the immediately following code in
block_size.rs, pipelined_gen.rs, and async_gen.rs. Reworks the few that
remain to focus on the WHY (upstream-derived phase 2 short-circuit, sqrt
bound derivation, BATCH_SIZE cross-file consistency, disk I/O thread cap).
Comment-only change with no functional impact.

* docs(metadata): convert restating comments to rustdoc in chmod (#2022) (#3473)

Remove section-banner comments and pure-restatement comments from
chmod test modules. Convert a stranded `///` doc-comment in
`upstream_compatibility` to a proper `//!` module doc. Preserve all
comments that reference upstream rsync semantics or that explain the
non-obvious conditional-X / assign-empty-perms / octal-validation
rules. No functional code changes.

* feat(ci): add upstream rsync testsuite harness (#3470)

Adds tools/ci/run_upstream_testsuite.sh, which runs upstream rsync's
testsuite/*.test scripts against oc-rsync. Mirrors upstream's
runtests.sh contract: exports $RSYNC, $TOOLDIR, $srcdir, $suitedir,
$scratchdir, $TLS_ARGS, $POSIXLY_CORRECT, and $ECHO_* per test.

Difference vs upstream runtests.sh: $RSYNC points at oc-rsync, not
upstream. Upstream sources are still needed for helper tools (tls,
getgroups, lsh.sh) and config artefacts (config.h, shconfig); the
harness fetches and configures them on first run.

Known failures live in tools/ci/upstream_testsuite_known_failures.conf
and are grouped by category (lsh.sh-routed remote-shell tests,
daemon-mode tests, ACL/xattr, devices, chown, hardlinks INC_RECURSE,
atimes/crtimes, etc). Tests in this list are reported XFAIL on failure
and UPASS on unexpected success so the list stays self-curating.

Wires up risk area #4 from the audit: protocol edge-case compatibility
against upstream's own conformance suite.

Usage:
  tools/ci/run_upstream_testsuite.sh           # all tests
  WHICHTESTS=00-hello.test tools/ci/...        # one test
  PRESERVE_SCRATCH=yes tools/ci/...            # keep per-test dirs

* docs: clean up comments in protocol::error_recovery (#1985) (#3472)

Remove restatement and decorative banner comments that echo the code
without adding value. Replace two banner-style remarks with focused
notes that explain non-obvious behavior (over-receive handling, why
HashMap re-insert is the desired semantic, the conservative default
classification, and the resume-vs-retry policy on transient errors).

Scope is limited to crates/protocol/src/error_recovery/. No functional
changes; tests and public APIs are unchanged.

Refs #1985

* docs(checksums): convert restating comments to rustdoc in strong (#2020) (#3469)

Audit of `crates/checksums/src/strong/` (excluding `strategy/`,
`md4_tests.rs`, `xxh64_tests.rs` per task scope). Production source files
are already well-documented from prior cleanup passes: every public type,
trait, function, and method carries rustdoc; upstream rsync references
(`upstream: checksum.c:get_checksum2()` and similar) are preserved on the
seed-handling paths in `md4.rs` and `md5.rs`; no decorative banners,
debug checkpoints, or commented-out code remain in scope.

The single substantive change in this pass adds a quirk comment to the
private `detect()` helper in `openssl_support.rs` that captures
non-obvious upstream behaviour: MD4 may be absent on OpenSSL builds
without the legacy provider, so the MD4 probe is best-effort and overall
detection succeeds as long as MD5 works. This explains the
otherwise-mysterious `if let Some(md4) = ...` whose result is
deliberately discarded.

No behaviour, signature, or import changes.

* docs(compress): convert restating comments to rustdoc in strategy (#2028) (#3468)

Remove decorative banner/divider comments from the compress::strategy
module. The module's rustdoc was already comprehensive; this cleanup
removes the remaining `// ---- Section ----` test-grouping banners
that violate the no-decorative-divider rule from <internal-tool-doc>.

All upstream rsync C source references and load-bearing internal
comments are preserved verbatim. No production code, function bodies,
signatures, types, or imports were modified.

* docs: add v0.6 known limitations and security hardening notes

Adds a "Known Limitations / Architectural Trade-offs" section to README.md
covering PBUF_RING 5.19+ requirement, io_uring buffer pool ceiling, SSH
double-compression interaction, single-thread delta computation, daemon TLS
gap, and Windows IOCP wiring status (#1868).

Updates SECURITY.md supported-versions table to 0.6.x and adds a "Hardening
Notes" section covering recycle_buffer release-mode bounds-check gap, bgid
u16 namespace exhaustion, SSH double-compression amplification surface,
daemon TLS-in-front guidance (stunnel / SSH tunnel / reverse proxy), and
daemon module hardening defaults.

Cross-links the two documents so operators planning a deployment have a
single source of truth for the documented trade-offs.

* docs: comment cleanup in protocol::flist::hardlink

Remove restating-the-code comments from the hardlink test suite and
fix two malformed upstream references in types.rs that used `// upstream:`
inside rustdoc blocks (rendered literally in generated docs).

Preserved: all upstream rsync source references, non-obvious WHY
explanations (FxHash collision rationale, swapped-value asymmetry,
weak-mixing input categorisation), and module-level documentation.

* docs(filters): audit .rsync-filter per-directory inheritance (#2050)

Compare oc-rsync's per-directory merge file inheritance against
upstream rsync 3.4.1. Documents the push/pop lifecycle, modifier
semantics (n, e, p, s, r, !), and parent-dirscan behaviour. Identifies
three behavioural bugs in FilterChain (n modifier ignored, !/clear
not propagated to scopes, include-only scopes cannot override outer
excludes), one intentional divergence (parent_dirscan), and one
untested area (nested dir-merge declarations).
oferchen added a commit that referenced this pull request May 5, 2026
* docs(fast_io): design session-level io_uring ring pool (#1409) (#3444)

* docs(fast_io): audit io_uring SQPOLL and DEFER_TASKRUN for socket I/O (#1267) (#3445)

* docs(ci): audit Windows ACL/xattr CI matrix gaps (#1869) (#3446)

* docs(fast_io): audit MADV_WILLNEED prefault for mmap'd basis files (#1662) (#3447)

* docs(batch): investigate zstd as batch-compatible compression alternative (#1685) (#3448)

* docs(fast_io): document mmap page-fault impact on io_uring SQPOLL (#1661) (#3449)

* docs: audit --delete-during ordering vs upstream rsync 3.4.1 (#3453)

Captures the audit findings from #1893 in
docs/architecture/delete-during.md and lays the groundwork for the
documentation work tracked in #1894. Contrasts upstream's per-directory
interleaved deletion (generator.c::recv_generator + delete_in_dir)
against oc-rsync's batched pre-transfer sweep
(crates/transfer/src/receiver/transfer.rs:532), enumerates the resulting
differences in phase ordering, determinism, filter evaluation, and error
semantics, and lists the follow-up actions: CHANGELOG / man-page note,
interop test for concurrent new+deleted entries, .rsync-filter
investigation, and a possible --delete-strict-order opt-in.

Refs #1893, #1894.

* feat: add --jump-host proxy-jump CLI flag (#3454)

Expose OpenSSH ProxyJump (-J) as --jump-host. Comma-separated
[user@]HOST[:PORT] hops are forwarded to the remote shell as
`ssh -J <value>` before the destination operand when the configured
remote shell is OpenSSH. Empty values are rejected at every layer.

Note: only the long form `--jump-host` is provided. Upstream rsync
3.4.1 binds `-J` to `--omit-link-times` (options.c:647), so reusing
the short flag would break wire compatibility.

Refs #1881

* docs: audit --iconv inert critical gap (#3455)

Document the parse-but-never-applied architectural dead-end where the
CLI accepts --iconv, validates and stores IconvSetting on ClientConfig,
and forwards the option to the remote peer over SSH, but the local
process never receives a FilenameConverter. ServerConfigBuilder::iconv()
exists with zero call sites; receiver and generator already pull a
converter from connection.iconv but always observe None.

Severity: critical. Filenames with non-ASCII bytes silently bypass
transcoding on every local-side path (file-list ingest, file-list emit,
filter matching, daemon module serving) when --iconv is supplied.

Companion to docs/audits/iconv-pipeline.md, narrowing on the single
missing IconvSetting -> FilenameConverter bridge that currently makes
every gap in that broader pipeline simultaneously unobservable.

Tracks tasks #1909, #1910, #1918. Remediation path enumerated against
existing #1911-#1919 task chain.

* fix: normalise Windows backslash to forward slash in wire-encoded paths (#3456)

A Windows oc-rsync sender that builds a `FileEntry` whose path was
constructed via `Path::join` / `PathBuf::push` (the normal case for
recursive transfers) emitted the native string with `\` separators
verbatim on the wire. A POSIX rsync receiver decoding those bytes
treated every `\` as part of a single filename, producing one literal
filename per source file instead of the expected directory hierarchy.

Upstream rsync 3.4.1 writes filename bytes verbatim in
`flist.c:send_file_entry()` (lines 534-570). The wire format remains
`/`-separated because every upstream build either runs on a POSIX
kernel or under Cygwin's POSIX layer, which presents `/`-separated
paths to the application before this code is reached. oc-rsync targets
native Win32 directly, so the sender must perform the separator
normalisation explicitly.

Before this fix on Windows:

    let mut path = PathBuf::from(\"subdir\");
    path.push(\"file.txt\");
    let entry = FileEntry::new_file(path, 1024, 0o644);
    entry.name_bytes() == b\"subdir\\\\file.txt\"   // wrong

After:

    entry.name_bytes() == b\"subdir/file.txt\"     // matches upstream

The fix introduces a single-purpose helper
`crates/protocol/src/flist/wire_path.rs::path_bytes_to_wire` that
mirrors the existing identity-on-Unix / convert-on-Windows pattern of
`wire_mode.rs`. The helper is applied at every wire-encode call site:

- `FileEntry::name_bytes()` (filename emission via `write_entry`)
- `write_symlink_target()` (symlink target emission)
- `strip_leading_slashes()` Windows branch trims both `/` and `\`

The `name_bytes()` accessor signature changes from `&[u8]` to
`Cow<'_, [u8]>` so the helper can borrow on Unix (zero allocation) and
own only when conversion is required on Windows. Sort comparators
borrow the inner slice via `Deref` and continue to work unchanged.

Tests added:
- `wire_path` module: 8 unit tests covering forward-slash identity,
  empty path, dot path, Unix borrow, Unix backslash preservation,
  Windows translation, mixed separators.
- `flist::write` regression tests: assert the wire-encoded filename
  contains no `\` byte and that a writer-then-reader roundtrip yields
  `subdir/file.txt` regardless of host platform.
- Symlink-target regression test asserting no `\` byte appears in the
  encoded target bytes.

Companion audit: docs/audits/windows-path.md cites upstream
flist.c:534-570 and util1.c:955-961.

Closes #1905
Refs #1939

* fix: validate IPv6 host with Ipv6Addr and support scoped zone ids (#3450)

* fix: validate IPv6 host with Ipv6Addr and support scoped zone ids

Closes #1879 and #1880.

The previous `host_contains_colon` heuristic in `SshCommand::target_argument`
treated any string containing `:` as IPv6 and wrapped it in brackets. That
silently accepted malformed input such as `2001:db8:::1` or `garbage:input`
and forwarded the unparseable literal to ssh.

Replace it with strict `Ipv6Addr::from_str` validation via a new
`parse_host_for_ssh` returning a `HostKind` enum (`Hostname` / `Ipv4` /
`Ipv6 { addr, zone }`). The parser also recognises RFC 4007 scoped zone
identifiers (e.g. `fe80::1%eth0`) and re-emits them inside the bracket
form (`[addr%zone]`) per upstream rsync convention. Zone ids are rejected
when empty or when they contain whitespace or `]`.

Before: `host_contains_colon("2001:db8:::1") == true` -> emits `[2001:db8:::1]`.
After:  `parse_host_for_ssh("2001:db8:::1")` returns `Err(InvalidIpv6)`, so
        the input is passed through unchanged and ssh surfaces the
        resolution failure instead of receiving a malformed bracketed
        literal.

Includes unit tests for: bare IPv4, bare hostname, bracketed IPv6, IPv6
with zone (`fe80::1%eth0` and `[fe80::1%en0]`), malformed multi-`::` IPv6,
zone with whitespace (rejected), and direct `parse_host_for_ssh`
classification across all `HostKind` and `BuildError` variants.

* style: apply cargo fmt to ssh ipv6 validation

* feat: add AppleDouble filter and optional xattr merge for macOS (#3457)

* feat: add AppleDouble filter for macOS sidecar exclusion (#1907)

Add the `--apple-double-skip` option which appends a perishable `._*`
exclusion to the filter chain. macOS writes AppleDouble sidecar files on
filesystems that cannot represent extended attributes natively (FAT,
exFAT, NFS, SMB) to carry FinderInfo, resource forks, and xattrs.
Replicating them across machines clutters destinations with stale
metadata.

The filter half of #1907 ships now. Upstream rsync 3.4.1 has no
equivalent flag, so the option uses the descriptive
`--apple-double-skip` name. The optional xattr merge half is deferred:
the existing `apple-fs` crate does not expose AppleDouble parsing or
xattr merging primitives, so a follow-up task will land that piece
alongside the required parser.

- New `filters::apple_double` module with the canonical `._*` pattern.
- `FilterSet::from_rules_with_apple_double` mirrors the
  `from_rules_with_cvs` convenience constructor.
- CLI plumbing through `ParsedArgs`, the command builder, the
  filter-rules collector, and the workflow runner.
- Integration tests under `crates/filters/tests/apple_double.rs`
  covering top-level/nested matching, perishable semantics, override
  precedence, and clear-rule interaction.
- Frontend tests cover argument parsing and an end-to-end transfer
  scenario that confirms `._foo` files are dropped while their parents
  copy through.
- Man page and `--help` text updated.

Refs #1907

* style: apply cargo fmt to apple-double filter

* refactor: use shell-words crate for ssh remote-shell parsing (#3451)

* refactor: use shell-words crate for ssh remote-shell parsing

Replace the bespoke byte-level state machine in `parse_remote_shell`
with `shell_words::split`, the well-supported POSIX shell tokenizer.

- Tokenization is delegated to the `shell-words` crate (1.1).
- The wrapper retains the three behaviours callers rely on:
  empty/whitespace input -> `Empty`, interior NUL -> `InteriorNull`,
  non-UTF-8 input -> `InvalidEncoding`.
- The historical `UnterminatedEscape`/`UnterminatedSingleQuote`/
  `UnterminatedDoubleQuote` variants collapse into a single
  `Parse(String)` variant carrying the `shell_words::ParseError`
  description. No external code matched on the removed variants.
- Adds a property test corpus (`crates/rsync_io/tests/parse_remote_shell.rs`)
  asserting parity with `shell_words::split` over arbitrary
  RSYNC_RSH-style inputs, plus explicit unit tests for the historical
  behaviours (quoting, escapes, whitespace, NUL byte, invalid Unicode).

Tasks: #1877, #1878.

* style: apply cargo fmt to ssh shell-words tokenizer tests

* chore: update Cargo.lock for shell-words dependency

Cargo.lock was not updated when shell-words = "1.1" was added to
crates/rsync_io/Cargo.toml in cc01bbc, causing the MSRV 1.88
workflow to fail with --locked.

* fix(ssh): reject trailing backslash escape in remote-shell tokenizer

shell_words::split silently accepts a dangling trailing backslash, but
upstream rsync (and the previous bespoke tokenizer) reject it. Add a
small validator that walks the string tracking single- and double-quote
regions so that backslashes inside single quotes are not flagged, and
returns true only when the input ends with an unescaped backslash that
has no character to escape.

This restores the test parser_rejects_trailing_escape that fails on the
shell-words crate alone.

* test: allow stricter Parse rejection vs shell_words in parity property

The bespoke remote-shell tokenizer rejects dangling trailing backslashes,
matching upstream rsync's `tokens = parse_arguments(...)`. The new
shell-words-based wrapper preserves that strictness via has_trailing_escape,
but `shell_words::split` silently absorbs the trailing backslash and returns
Ok. The parity property test was therefore failing on inputs ending in a
bare `\\` because parse_remote_shell returned Err(Parse) while shell_words
returned Ok.

The wrapper is intentionally a tightening, not a parity match in both
directions. Add an explicit (Err(Parse), Ok(_)) arm so the property test
encodes the contract: we may reject inputs shell_words accepts, but never
the other way around.

* chore: disable coverage workflow on push/pull_request (#3460)

Nightly llvm-cov 22.1 SIGSEGVs deterministically inside
llvm::coverage::CoverageMapping::getInstantiationGroups, breaking
both master and PR runs. Restrict the workflow to manual
workflow_dispatch until a known-good nightly is pinned via
RUSTUP_TOOLCHAIN.

* fix: avoid mmap basis when paired with io_uring writer (#3459)

* fix: avoid mmap basis when paired with io_uring writer

DeltaApplicator opened its basis file via MapFile::open_adaptive, which
selects mmap for files >= 1 MiB on Unix. The applicator has no
production caller today, but is the obvious next target for an
io_uring-output rewrite. Wiring an IoUringWriter to the applicator
without changing the basis path would submit mmap-backed pointers to
io_uring SQEs on block-ref copies >= the writer batch threshold,
exposing two failure modes:

1. Cold-page faults on the basis file are serviced under the SQE
   submission thread (worse, the SQPOLL kernel thread when SQPOLL is
   enabled), turning a "free" zero-copy write into a synchronous fault
   and stalling other in-flight SQEs on the same poller.
2. Concurrent truncation of the basis file raises SIGBUS while the
   kernel is dereferencing the page on our behalf - recovery from
   in-kernel SIGBUS is not signal-safe.

Upstream rsync 3.4.1 deliberately avoids mmap(2) for basis files for
the same truncation reason (fileio.c:214-217). Our BufferedMap matches
that decision.

Closes the F1 hazard from docs/audits/mmap-iouring-co-usage.md (#1660)
by introducing BasisWriterKind in DeltaApplyConfig: when the writer is
io_uring-backed, DeltaApplicator::new opens the basis via the new
MapFile::open_adaptive_buffered (forces AdaptiveMapStrategy::Buffered
regardless of size). Standard / std-write writers retain the existing
adaptive selection. Non-Unix is unaffected since BufferedMap is the
only basis strategy there.

Tests cover both directions: io_uring writer + 2 MiB basis stays on
BufferedMap, standard writer + 2 MiB basis still picks mmap on Unix.
docs/design/basis-file-io-policy.md updated with implementation status
noting that the io_uring-pairing axis is now wired; remaining hazard
columns (--inplace, --append, --copy-devices, sparse, network FS) are
future work tracked in the same doc.

Refs: #1906 (this task), #1660 (audit).

* fix: drop redundant Write import in applicator tests

The test module brings in `Write` via `use super::*;` which re-exports
the file-level `use std::io::{self, Read, Write};`. The explicit
`use std::io::Write as _;` is therefore unused and trips clippy under
`-D warnings`.

* feat: bridge IconvSetting to FilenameConverter (#3458)

Adds IconvSetting::resolve_converter() to map the CLI-side iconv
setting onto a transfer-side FilenameConverter, and wires the
converter through apply_common_server_flags so every SSH and daemon
ServerConfig builder populates ConnectionConfig.iconv when --iconv
is in effect. Without this bridge, the CLI parsed --iconv, validated
it, forwarded it to the remote peer over SSH, but the local file-list
reader and writer hooks always observed None and silently passed raw
bytes through.

Also rejects --iconv=LOCAL,REMOTE with a hard error when the iconv
cargo feature is compiled out, rather than silently no-opping.

Closes #1911
Closes #1915

* perf: wire IoUringDiskBatch into disk_commit hot path (#3452)

* perf: wire IoUringDiskBatch into disk_commit hot path

Task #1901. The disk-commit thread previously created an IoUringDiskBatch
via try_create_disk_batch() but bound it to `_disk_batch`, leaving every
write to fall through to the buffered path (thread.rs:127). All disk
writes therefore bypassed io_uring batching even when the policy was Auto
or Enabled on Linux 5.6+.

Introduce a Writer enum in disk_commit/writer.rs that dispatches between
ReusableBufWriter (existing 256 KB buffered path) and a new IoUring
variant that borrows the disk thread's persistent IoUringDiskBatch. The
IoUring variant is cfg-gated to all(target_os = "linux", feature =
"io_uring") so non-Linux builds never reference it.

In disk_commit/thread.rs, drop the underscore from the batch binding and
thread `disk_batch.as_mut()` into both process_file and process_whole_file
on every iteration of the message loop. The batch is created once per
thread and reused across all files via begin_file/commit_file.

In disk_commit/process.rs, replace the unconditional ReusableBufWriter
construction with a make_writer() helper that registers the file with
the batch when (a) the batch is present and (b) sparse mode is disabled.
Sparse writes require Seek, which IoUringDiskBatch does not implement,
so sparse mode keeps using the buffered writer via buffered_for_sparse().

Semantics preserved:
- Temp-file commit ordering: Writer::finish() calls commit_file(do_fsync)
  which flushes + fsyncs + detaches the file before commit_file() runs
  the rename. Buffered path drops the writer (closing the file) before
  rename, identical to prior behaviour.
- fsync: do_fsync flag flows through Writer::flush_and_sync (buffered)
  and Writer::finish (io_uring). The io_uring path makes flush_and_sync
  a no-op so commit_file performs both atomically in a single SQE.
- Error propagation: io::Result is preserved end-to-end with file_path
  context attached on fsync/commit errors.

* fix: gate unused Writer::finish parameters on non-Linux builds

The do_fsync and file_path parameters on Writer::finish are only
consumed by the io_uring arm. On non-Linux (or with the io_uring
feature disabled) the Buffered arm ignores them, which under
-D warnings escalates to a build failure.

* fix(disk_commit): force buffered writer for append mode

The IoUringDiskBatch writes via SQEs with absolute offsets starting at 0,
ignoring the file position set by `file.seek(append_offset)` in
open_output_file. This caused --append-mode transfers under io_uring to
overwrite the existing file prefix with zeros, surfacing as the
standalone:append interop test failing with NUL-byte corruption.

Gate Writer::IoUring off whenever begin.append_offset > 0 and route those
transfers through ReusableBufWriter, which honors the seek via standard
Write::write_all.

upstream: receiver.c:307-308 - file position is the source of truth in
append mode; any writer that ignores it cannot be used.

* docs(compress): convert restating comments to rustdoc in lz4 (#2026) (#3462)

Remove inline comments inside lz4 codec function bodies and tests
that simply echo the next statement. All public-item rustdoc and
upstream rsync references (token.c) remain intact.

* fix(filters): propagate P (protect) filter modifier in sender-side filter exchange (#3463)

oc-rsync was emitting `P pattern` directly on the wire while also
attaching the `r` (receiver-side) modifier derived from the rule's
`applies_to_receiver` flag. Upstream rsync rejects `Pr` because the
`P` prefix already specifies the side and `r` after a side-specifying
prefix triggers the "invalid modifier" error in exclude.c:1270-1271.

Upstream's `get_rule_prefix()` (exclude.c:1536-1572) only ever emits
`+`, `-`, or `:` as the leading character; `P` and `R` exist only as
parser sugar that lower to plain include/exclude rules carrying the
`FILTRULE_RECEIVER_SIDE` flag. The wire encoding for a P rule is
`-r pattern`; the wire encoding for an R rule is `+r pattern`.

Normalize Protect/Risk in `build_modern_prefix` so the wire stream
matches upstream byte-for-byte. The receiver-side flag is forced when
serializing Protect/Risk rule types so that hand-built
`FilterRuleWireFormat` values without `receiver_side=true` still
serialize correctly.

Reproduced and verified the fix against upstream rsync 3.4.1 daemon
in the rsync-profile podman container with
`--filter='P *.log'` push: protected files now survive `--delete`.

Removes `standalone:delete-filter-protect` from KNOWN_FAILURES and
DASHBOARD_ENTRIES.

upstream: exclude.c:1536-1542
upstream: exclude.c:1569-1572
upstream: exclude.c:1201-1206

* docs(checksums): convert restating comments to rustdoc in rolling (#2018) (#3461)

Cleans up the `crates/checksums/src/rolling/` test modules:

- Drop decorative banner divider in front of the golden-tests block; replace with a
  short paragraph that describes intent and references upstream checksum.c.
- Remove restating-the-code comments (e.g. "Verify it matches manual computation",
  "Verify rolling produces correct checksum after shift") whose information is
  already conveyed by the surrounding code or test name.
- Sharpen wire-format comments to call out their connection to upstream rsync's
  packed (s2 << 16) | s1 layout.

Production source files in `rolling/` already use proper rustdoc on every public
item, so no `///` conversions are required there. SAFETY comments and SIMD
weight-table explanations are preserved verbatim. No runtime behaviour changes.

* fix(checksums): apply checksum_seed to MD4 strong checksum (upstream parity) (#3465)

Upstream rsync's `get_checksum2()` (checksum.c:358-396) appends the negotiated
`checksum_seed` after the data when computing MD4 block strong sums:

    memcpy(buf1, buf, len);
    if (checksum_seed) {
        SIVAL(buf1, len, checksum_seed);
        len += 4;
    }

Our MD4 path was unconditionally calling `Md4::digest(data)` and ignoring the
seed, so block-level strong checksums diverged from upstream whenever the
session negotiated a non-zero seed. This silently hurt delta-transfer match
quality across rsync<->oc-rsync interop and inflated `hash_hits` /
`false_alarms` counters in delta-stats output.

Changes:

* Add `Md4::digest_with_seed(seed, data)` mirroring upstream's append-seed-
  after-data semantics. A zero seed is a no-op (matches upstream's
  `if (checksum_seed)` guard).
* Add `SignatureAlgorithm::Md4Seeded { seed }` variant. Introducing a new
  variant rather than mutating the unit `Md4` keeps the 30+ existing
  call-sites that match on `Md4` working.
* `ChecksumFactory::signature_algorithm()` now selects `Md4Seeded` when MD4
  (or the legacy `None`/protocol<27 default) runs with a non-zero seed, and
  keeps unit `Md4` for the seed=0 case so existing wire goldens stay byte-
  identical.
* Extend exhaustive matches in `signature::algorithm`, the parallel
  checksum executor, and the delta-transfer bench to cover `Md4Seeded`.

Tests:

* `md4_seeded_appends_seed_after_data` - verifies the byte layout matches
  building `(data || seed_le_bytes)` and hashing with plain MD4.
* `md4_seeded_zero_seed_matches_unseeded` - guards the upstream zero-seed
  short-circuit.
* `md4_seeded_negative_seed_is_le_two_complement` - confirms i32 wire
  encoding for negative seeds.
* `md4_seeded_signature_matches_upstream_format` - parity at the
  `SignatureAlgorithm` layer.
* Three `ChecksumFactory` tests covering MD4/None x seed=0/non-zero.

upstream: checksum.c:358-396 `get_checksum2()` MD4 branch

* fix(filters): correct R-before-P ordering in delete-filter-risk interop test (#3464)

* fix(filters): correct R-before-P ordering in delete-filter-risk interop test

The standalone:delete-filter-risk interop test had the filter rules in the
wrong order: --filter='P *.log' --filter='P *.sh' --filter='R *.log'.

Upstream rsync evaluates filter rules first-match-wins (exclude.c:1038-1065
check_filter()). For R (risk) to override P (protect) on *.log, it must be
listed BEFORE the P rule. With R last, the P rule matched first and the
*.log files were never deleted.

Verified that upstream rsync 3.4.1 itself produces the same "wrong"
outcome with the original P-first ordering, confirming the test
expectation - not the filter engine - was incorrect. oc-rsync's filter
engine already mirrors upstream semantics; the unit test
risk_rule_allows_deletion_before_protection in crates/filters/src/tests.rs
explicitly documents the required R-before-P order.

Reordered both directions (up->oc and oc->up) to use
--filter='R *.log' --filter='P *.log' --filter='P *.sh' and updated the
function-level comment to cite exclude.c:1201-1207 (R rflags) and
exclude.c:1038-1065 (first-match-wins). Verified end-to-end in the
rsync-profile container that both upstream->oc and oc->upstream daemon
pushes now produce the expected outcome:
  - source files transferred
  - risky.log + subdir/nested.log deleted (R overrides P)
  - keeper.sh preserved (P with no preceding R)
  - destonly.txt deleted (no protection)

Removed the entry from KNOWN_FAILURES and DASHBOARD_ENTRIES in
tools/ci/known_failures.conf.

upstream: exclude.c:1201-1207 'R' = FILTRULE_INCLUDE|FILTRULE_RECEIVER_SIDE
upstream: exclude.c:1038-1065 check_filter() first-match-wins

* fix(filters): suppress redundant r/s modifier on Risk/Protect wire prefix

The wire encoder unconditionally emitted `s`/`r` modifiers when the
sender_side/receiver_side flags were set on a FilterRuleWireFormat.
This produced output like `Rr *.log` for a Risk rule (which oc-rsync
internally tags as receiver-side). Upstream rsync's parser rejects
that with `invalid modifier 'r' at position 1 in filter rule`,
breaking the delete-filter-risk interop scenario in oc->upstream
direction with exit 12.

Upstream's filter parser (exclude.c:1180-1207) sets
prefix_specifies_side when the rule type char is R/P (and S/H), and
exclude.c:1269-1278 rejects an explicit `r`/`s` modifier in that case.
Match upstream's get_rule_prefix (exclude.c:1525-1587), which never
emits the redundant flag for those prefixes.

Suppress `s`/`r` emission when the rule type is Risk or Protect.
Add unit tests at the prefix builder level and wire-level tests
including a Risk roundtrip to lock in the format.

* docs(protocol): convert restating comments to rustdoc in varint (#1999) (#3466)

Remove decorative banner comments from the varint test module and
tighten internal comments in `read_varlong` to delete pure restatement
while preserving upstream rsync C source references (`io.c:read_varlong`,
`memcpy(u.b, b2+1, min_bytes-1)`).

No behaviour, signature, or import changes.

* docs(compress): convert restating comments to rustdoc in zlib (#2029) (#3467)

Remove decorative and restating-the-code comments from the zlib
module's tests, while preserving every upstream rsync C source
reference and comments that explain non-obvious test design
rationale. Non-test files (decoder.rs, encoder.rs, helpers.rs,
level.rs, mod.rs) already use proper rustdoc and required no
changes.

* docs: clean up comments in core::timeout (#2014) (#3471)

* docs(signature): convert restating comments to rustdoc (#2034) (#3474)

Drops inline comments that merely echo the immediately following code in
block_size.rs, pipelined_gen.rs, and async_gen.rs. Reworks the few that
remain to focus on the WHY (upstream-derived phase 2 short-circuit, sqrt
bound derivation, BATCH_SIZE cross-file consistency, disk I/O thread cap).
Comment-only change with no functional impact.

* docs(metadata): convert restating comments to rustdoc in chmod (#2022) (#3473)

Remove section-banner comments and pure-restatement comments from
chmod test modules. Convert a stranded `///` doc-comment in
`upstream_compatibility` to a proper `//!` module doc. Preserve all
comments that reference upstream rsync semantics or that explain the
non-obvious conditional-X / assign-empty-perms / octal-validation
rules. No functional code changes.

* feat(ci): add upstream rsync testsuite harness (#3470)

Adds tools/ci/run_upstream_testsuite.sh, which runs upstream rsync's
testsuite/*.test scripts against oc-rsync. Mirrors upstream's
runtests.sh contract: exports $RSYNC, $TOOLDIR, $srcdir, $suitedir,
$scratchdir, $TLS_ARGS, $POSIXLY_CORRECT, and $ECHO_* per test.

Difference vs upstream runtests.sh: $RSYNC points at oc-rsync, not
upstream. Upstream sources are still needed for helper tools (tls,
getgroups, lsh.sh) and config artefacts (config.h, shconfig); the
harness fetches and configures them on first run.

Known failures live in tools/ci/upstream_testsuite_known_failures.conf
and are grouped by category (lsh.sh-routed remote-shell tests,
daemon-mode tests, ACL/xattr, devices, chown, hardlinks INC_RECURSE,
atimes/crtimes, etc). Tests in this list are reported XFAIL on failure
and UPASS on unexpected success so the list stays self-curating.

Wires up risk area #4 from the audit: protocol edge-case compatibility
against upstream's own conformance suite.

Usage:
  tools/ci/run_upstream_testsuite.sh           # all tests
  WHICHTESTS=00-hello.test tools/ci/...        # one test
  PRESERVE_SCRATCH=yes tools/ci/...            # keep per-test dirs

* docs: clean up comments in protocol::error_recovery (#1985) (#3472)

Remove restatement and decorative banner comments that echo the code
without adding value. Replace two banner-style remarks with focused
notes that explain non-obvious behavior (over-receive handling, why
HashMap re-insert is the desired semantic, the conservative default
classification, and the resume-vs-retry policy on transient errors).

Scope is limited to crates/protocol/src/error_recovery/. No functional
changes; tests and public APIs are unchanged.

Refs #1985

* docs(checksums): convert restating comments to rustdoc in strong (#2020) (#3469)

Audit of `crates/checksums/src/strong/` (excluding `strategy/`,
`md4_tests.rs`, `xxh64_tests.rs` per task scope). Production source files
are already well-documented from prior cleanup passes: every public type,
trait, function, and method carries rustdoc; upstream rsync references
(`upstream: checksum.c:get_checksum2()` and similar) are preserved on the
seed-handling paths in `md4.rs` and `md5.rs`; no decorative banners,
debug checkpoints, or commented-out code remain in scope.

The single substantive change in this pass adds a quirk comment to the
private `detect()` helper in `openssl_support.rs` that captures
non-obvious upstream behaviour: MD4 may be absent on OpenSSL builds
without the legacy provider, so the MD4 probe is best-effort and overall
detection succeeds as long as MD5 works. This explains the
otherwise-mysterious `if let Some(md4) = ...` whose result is
deliberately discarded.

No behaviour, signature, or import changes.

* docs(compress): convert restating comments to rustdoc in strategy (#2028) (#3468)

Remove decorative banner/divider comments from the compress::strategy
module. The module's rustdoc was already comprehensive; this cleanup
removes the remaining `// ---- Section ----` test-grouping banners
that violate the no-decorative-divider rule from <internal-tool-doc>.

All upstream rsync C source references and load-bearing internal
comments are preserved verbatim. No production code, function bodies,
signatures, types, or imports were modified.

* docs: add v0.6 known limitations and security hardening notes

Adds a "Known Limitations / Architectural Trade-offs" section to README.md
covering PBUF_RING 5.19+ requirement, io_uring buffer pool ceiling, SSH
double-compression interaction, single-thread delta computation, daemon TLS
gap, and Windows IOCP wiring status (#1868).

Updates SECURITY.md supported-versions table to 0.6.x and adds a "Hardening
Notes" section covering recycle_buffer release-mode bounds-check gap, bgid
u16 namespace exhaustion, SSH double-compression amplification surface,
daemon TLS-in-front guidance (stunnel / SSH tunnel / reverse proxy), and
daemon module hardening defaults.

Cross-links the two documents so operators planning a deployment have a
single source of truth for the documented trade-offs.

* docs: comment cleanup in protocol::flist::hardlink

Remove restating-the-code comments from the hardlink test suite and
fix two malformed upstream references in types.rs that used `// upstream:`
inside rustdoc blocks (rendered literally in generated docs).

Preserved: all upstream rsync source references, non-obvious WHY
explanations (FxHash collision rationale, swapped-value asymmetry,
weak-mixing input categorisation), and module-level documentation.

* docs(engine): audit --fuzzy basis-file search algorithm (#2051)

Document oc-rsync's --fuzzy / -y basis-file search and scoring
against upstream rsync 3.4.1 (generator.c::find_fuzzy() and
util1.c::fuzzy_distance()). Identifies six divergences (scoring
metric, phase A size+mtime short-circuit, FNAMECMP_FUZZY wire
emission, suffix heuristics, already-sent filtering, tie-breaker
direction) and three matches (-yy plumbing, --whole-file/--inplace
/--append interactions). Recommends Levenshtein-based scoring,
phase A short-circuit, and ITEM_BASIS_TYPE_FOLLOWS emission.
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