fix(tests): replace pipefail-racy echo | grep -q with here-strings

Why

Two suites failed intermittently — tests/test-vale-wrap.sh case 21 and
tests/test-check-release-needed.sh cases 4 and 15 — on correct output, and never
when run alone. The cause is the `echo "$OUT" | grep -q P` idiom under
`set -o pipefail`: grep -q exits as soon as it has an answer, bash's echo can
hand a multi-line value to the pipe one line at a time, and a write after the
reader is gone kills echo with SIGPIPE. pipefail then reports the writer's
death, so output that DID match reads as "no match". Every observed failure had
lines after its match; case 15's match is on line 1 of 6, the widest window in
that file.

Forced with a pause before the writer's last line, the pipe form failed 50 of 50
runs; a here-string, a match on the last line, and the same pipe without
pipefail each passed 50 of 50. Unforced the rate is about 1 per 670 suite runs,
which is why it read as a flaky gate rather than a bug.

The failures at review time are consistent with this, but were not proven to be
it: the suite was running while agents edited live config files in place, and a
brief change to .vale.ini or .pre-commit-hooks.yaml would produce the same two
failures. The race is real and fixed either way.

Implementation Notes

`grep -q P <<< "$VAR"` has no separate writer process, so there is nothing to
race. It is not a retry or a sleep. 121 sites converted across 9 files, three of
them scripts rather than tests: new-agent.sh, new-skill.sh and
check-executables-allow-sync.sh. None ships via .pre-commit-hooks.yaml, so no
external consumer pins them, and all three are single-pipeline checks whose
verdict cannot change.

Left alone deliberately: 14 sites whose writer is a command, not a shell
builtin — they either absorb the writer's status with `|| true` or are python3
and awk, which write once at exit — and one file with no pipefail. `printf '%s'`
sites differ from a here-string only by a trailing newline, which no -q verdict
on a non-empty pattern depends on.

tests/test-no-pipefail-early-exit-grep.sh is a static guard against new
occurrences, discovered automatically by run-tests.sh. It only scans files that
set pipefail, joins continuation lines, skips comments, and flags only
echo/printf writers. Its first case proves the scanner can fail before its
second trusts a clean verdict on the tree.

A guard covers exactly the spellings its regex models, so the miss surface was
measured rather than assumed. Four were found and closed: pipefail declared as
`set -o errexit -o pipefail` (where the old pattern required pipefail to follow
the FIRST -o, and a file-level miss skips every site in that file); a writer
separated from grep by an intermediate stage; a pipeline wrapped on a trailing
`|` rather than a backslash; and readers spelled egrep, fgrep, /bin/grep,
`command grep` or with an env-var prefix. Segment characters exclude a bare `&`
so `echo ok && other | grep -q x`, whose writer is `other`, does not false-fire.
Widening surfaced 5 live sites invisible to the original scanner, all in
tests/test-apm-current-hook.sh, all `echo "$out" | json_field ... | grep -q`;
they are safe today only because json_field is python3, which reads to EOF and
writes once. Fixtures go 4 to 12 vulnerable spellings plus near-miss negatives.

Two `grep ... | head -1` sites (test-vale-wrap.sh) are the same race with a
different early-exiting reader, and are fixed by absorbing the writer. The
scanner deliberately does not model `head`, `sed -n 1p` or a bare `read`: most
legitimate uses in this tree are already absorbed with `|| true` and the scanner
cannot see absorption from pipeline text, so a high false-positive rate would be
how this guard gets weakened. Heredoc bodies are scanned as code; none in the
tree trips it today.

Impact

The bug predates the factory-audit merge: every converted site in
check-release-needed and case 21 dates to 4d018af and aa8cc22 (2026-08-09).

Test suites go 19 to 20. `run-tests.sh --strict` passes 20/20 with 0 skipped,
four consecutive runs.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YR2CjVumUbEGWcMikcoXBD

SIMPLIFICATION-AUDIT.md

@@ -83,7 +83,7 @@ Where the 276 s goes (each suite run alone, sequential):
 
 Five suites account for 215 s of 276 s. Three of those five (sync-plugin-content, vale-style-sync, adr0020-differential) test tooling that findings 2, 7, and 14 propose to delete or shrink, so the fastest path to a quick pre-push is removing the duplication those tests guard rather than optimising the tests.
 
-> **Also struck (2026-09-15):** `test-check-vale-style-sync.sh` (25 s) went with the `check-vale-style-sync` hook in finding 14's merge (ADR-0025). Measured at HEAD: `tests/` holds **19** `test-*.sh` suites and `tests/run-tests.sh` reports `19 passed, 0 skipped, 0 failed`. Same basis as the note below — arithmetic on the 2026-09-10 baseline minus the struck rows, not a fresh timing run.
+> **Also struck (2026-09-15):** `test-check-vale-style-sync.sh` (25 s) went with the `check-vale-style-sync` hook in finding 14's merge (ADR-0025). Measured at HEAD: `tests/` holds **19** `test-*.sh` suites and `tests/run-tests.sh` reports `19 passed, 0 skipped, 0 failed`. (Later the same day, the pipefail-race fix added `tests/test-no-pipefail-early-exit-grep.sh`, making it **20**. That suite is a static scan and runs in well under a second, so the timing arithmetic here is unaffected.) Same basis as the note below — arithmetic on the 2026-09-10 baseline minus the struck rows, not a fresh timing run.
 
 > **Done (2026-09-14):** see commit `718c79a` on `docs/simplification-audit`. The three struck-through rows are gone: `test-sync-plugin-content.sh` (83 s, 1,289 lines, 92 cases), `check-plugin-content-sync` (4.5 s) and `validate-plugins` (4.9 s). Expected, not re-measured: roughly 92 s comes off every push (83 + 4.5 + 4.9 = 92.4 s) (~83 s of it out of `run-tests`, which loses its single slowest suite), on the arithmetic of the 2026-09-10 figures alone. The remaining rows have not been re-timed since, so treat every number in this section as the 2026-09-10 baseline minus those three, not as a fresh measurement.