rsync: output filter destroys verbose/dry-run transfer listing — redirected output captures 'ok (synced)' instead of the file list

Version: rtk 0.38.0 (reproduced); the responsible filter is unchanged on develop (src/filters/rsync.toml: { pattern = "total size is", message = "ok (synced)", unless = "error|failed|No such file" }), so this should still reproduce on v0.43.0.

Summary

The rsync output filter replaces the entire verbose / dry-run transfer listing with a one-line ok (synced) summary. When stdout is redirected or piped, the file or consumer receives the summary instead of the listing — silently corrupting any programmatic use of rsync's output.

Repro

mkdir -p /tmp/demo/src /tmp/demo/dst
for i in $(seq 1 100); do echo "content $i" > "/tmp/demo/src/f$i.txt"; done

# Through rtk:
rtk rsync -aLnv /tmp/demo/src/ /tmp/demo/dst/ > /tmp/out.txt
wc -l < /tmp/out.txt      # 1  (the file contains "ok (synced)")

# Native:
rsync -aLnv /tmp/demo/src/ /tmp/demo/dst/ > /tmp/native.txt
wc -l < /tmp/native.txt   # 100+ (real incremental file list)

Why this is a bug and not just compaction

With -n (dry run) and/or -v/-i, the transfer listing is the requested output — the whole point of the invocation is to enumerate what would transfer. There is no "safe" compact form of it. Downstream consumers that count or diff the listing (e.g. > file && wc -l < file, | grep -c) get answers derived from ok (synced) and reach false conclusions (in our case, several hours of debugging a healthy sync setup that the filtered output made look broken).

Expected behavior

One of:

• Exempt -n / -v / -i invocations from the rsync filter (the listing is the payload), or
• Don't apply output filters when stdout is not a TTY — this is the general class tracked in #1282, with #1841 as the proposed TOML-filter fix (see also #1060).

This report adds a concrete rsync-specific data point to that class: the filter's information loss isn't cosmetic, it inverts the meaning of dry-run output.

Start with src/filters/rsync.toml and reproduce the redirected-output commands in the issue, comparing rtk with native rsync. Review the related output-filter discussions in #1282, #1841, and #1060 before choosing the scope. Done means verbose, itemized, or dry-run listings remain available to redirected and piped consumers instead of being replaced by the summary.