fix: wait for transcript to stabilize in Stop hook (race with writer)

[evansenter]

Summary

The Stop hook shipped in PR #303 / fixed in #307 still doesn't reliably fire in production because it races Claude Code's transcript writer. At hook-run time, the current turn's final text block is often not yet flushed to transcript_path — only the preceding thinking block is visible — so the regex matches nothing and the hook declines to block.

Empirical evidence

Over 4 deliberate-violation tests this session:

#	Context	Hook duration	Blocked?
1	Broken regex	141ms	❌ (regex)
2	Fixed regex, clean hook	49ms	❌ (lost race)
3	Fixed regex + debug logging (~10ms overhead)	n/a	✅ (won race)
4	Fixed regex, clean hook	334ms	❌ (still lost race)

Hook duration is not the determining factor — test 4's 334ms hook still lost. What matters is wall-clock timing of the transcript write relative to hook start, which varies between turns independent of hook speed.

Full diagnostic broadcast to event bus: gotcha_discovered event #4028.

Fix

Poll wc -l on the transcript every 100ms at the start of the analysis phase; break when the line count is unchanged across two samples. Hard-cap at 1s to prevent hangs.

prev_lines=-1
for _ in 1 2 3 4 5 6 7 8 9 10; do
    cur_lines=$(wc -l < "$TRANSCRIPT_PATH" 2>/dev/null || echo 0)
    [[ "$cur_lines" -eq "$prev_lines" ]] && break
    prev_lines=$cur_lines
    sleep 0.1
done

• Typical latency: 100-200ms (one or two polls before stability).
• Worst case: 1s (transcript never stabilizes).
• Chosen over fixed sleep 0.3: adaptive; pays latency only when actually racing; resilient on slow machines where the race may be longer.

README updates

• Hook docstring (Actions step 3): added the wait step between "transcript path check" and "parse JSONL".
• Gotchas section: added a paragraph about the Stop-hook / transcript-writer race, recommending the same pattern for any content-inspecting Stop hook.

Follow-up worth considering

This is a platform gap: any Stop hook that inspects the current turn's content hits this race. A cleaner fix would live in Anthropic's Claude Code — pass the current turn's message content in the Stop hook's stdin JSON alongside transcript_path. Worth reporting upstream.

Test plan

• make check passes (29/29 bootstrap + 88/88 hooks)
• shellcheck --severity=error clean
• Existing tests still pass (static fixtures converge in 2 samples = 100ms extra per test)
• Live-validate via deliberate-violation test in a fresh session after merge

Live validation of this fix will happen the same way that caught the original bug: restart CC, emit an insight without publishing, observe the hook blocks reliably.

🤖 Generated with Claude Code

[claude]

Code Review

Summary: Well-diagnosed race fix. The quiescence-polling approach is reasonable, the hard cap protects against pathological cases, the short-circuits (no jq / no transcript / stop_hook_active) remain ahead of the wait loop so graceful-degradation and infinite-loop-prevention paths do not incur any latency, and the README/docstring updates are thorough. All findings below are suggestions.

Verdict: APPROVE - No Critical or Important issues. All findings are suggestions; they are posted in this body (inline posting via gh api failed repeatedly due to sandbox constraints in this review environment).

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Suggestion 1 - home/.claude/hooks/enforce-insight-publish.sh:41
The prev_lines=-1 sentinel forces at least one sleep 0.1 even when the transcript is already stable (common case in tests and non-racing turns). You could initialize prev_lines from an initial wc -l read before the loop - you still need two equal samples to declare stability, but the first observation is free. Minor; 100ms is well within any Stop budget.

Suggestion 2 - home/.claude/hooks/enforce-insight-publish.sh:47
Quiescence detection can be fooled by a writer that pauses >=100ms between consecutive flushes (two identical samples declare stability even though more lines are coming). Given the PR empirical data (race window under 100ms on the fast machine tested), this is an acceptable trade-off, but worth calling out as a known limitation in the comment or the hooks README gotcha - otherwise a future reader debugging a slow-writer regression will not have the context to understand why the detector gave up too early.

Suggestion 3 - home/.claude/hooks/enforce-insight-publish.sh (tests)
No automated test covers the new quiescence loop itself - existing fixtures in tests/test-hooks.sh are all static files, so they exercise the stable-on-first-comparison path but not the grew-then-stabilized path that this fix exists for. A background-writer test (append a line to the transcript after ~50ms, then invoke the hook) would verify the loop actually catches late writes and does not race-and-return early. Live validation via deliberate violation is still the gold standard, but a regression test would catch a future refactor that inadvertently removes the wait.

Suggestion 4 - home/.claude/hooks/enforce-insight-publish.sh:40 (comment text)
See PR discussion for empirical data will rot once the PR is forgotten. Consider inlining the key number (e.g., 3/4 firings lost this race on a fast machine; race window observed under 100ms) or pointing at the gotcha paragraph in hooks/README.md, which is in-repo and easier to rediscover than a PR URL.

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Automated review by Claude Code

[evansenter]

Feedback Addressed

Implemented

• [Suggestion] Add dark mode theme switching for btop and iTerm2 #1 — prev_lines initialized from a pre-loop wc -l read; already-stable turns now exit on the first comparison (typical latency ~100ms instead of ~200ms).
• [Suggestion] Add Claude Code GitHub Workflow #2 — Added a known-limitation comment above the loop: a writer pausing ≥100ms between flushes can fool the detector. Documented as acceptable trade-off given observed sub-100ms race windows.
• [Suggestion] refactor: Make git pull opt-in and skip unchanged LaunchAgent reload #4 — Replaced the ephemeral "See PR discussion" comment with a pointer to the Gotchas entry in hooks/README.md.

Skipped

• [Suggestion] Refactor sync to use home/ directory #3 — Background-writer test for the quiescence loop. Bash-level tests that simulate a race to test race-handling are inherently flaky; the cost of CI false-positives outweighs catching an inadvertent refactor. Live-validation via deliberate insight-without-publish in a fresh session remains the gold standard (and the reviewer agrees).

[claude]

Code Review — Summary: Targeted race fix for the Stop hook. Quiescence polling (wc -l every 100ms, break on two equal samples, 1s hard cap) is a pragmatic workaround for a Claude-Code-platform gap. The hook short-circuits (no jq, no transcript, stop_hook_active) remain ahead of the wait loop so the graceful-degradation and infinite-loop-prevention paths still cost nothing. README docstring (step 3) and the new Gotchas paragraph both accurately describe the fix, and the inline comment cross-references the Gotchas entry rather than a PR URL that would rot. Previously Addressed (Filtered): All three items implemented in the prior review round are in the code: (1) prev_lines initialized from pre-loop wc -l at line 46 - already-stable turns exit on the first comparison (~100ms); (2) Known-limitation comment above the loop at lines 42-45 re: writer pauses >=100ms between flushes; (4) Inline comment now points at the Gotchas entry in hooks/README.md at lines 38-40 instead of the ephemeral PR discussion. Item 3 (background-writer test) was skipped with sound rationale - bash-level tests that simulate races to verify race handling are inherently flaky. Live deliberate-violation remains the gold standard. I agree. Verdict: APPROVE - No Critical or Important issues. Fix is correct, scoped, and well-documented. --- Automated review by Claude Code