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memory: review-feedback fanout (parallel-session race at REQUEST_CHANGES time) #23

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WillTaylor22 merged 3 commits into from
May 26, 2026
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memory: review-feedback fanout (parallel-session race at REQUEST_CHANGES time) #23

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b76d753
memory: note duplicate-session race when reviewer leaves multiple REQ…
WillTaylor22 May 26, 2026
3ea23b1
memory: index entry for review-feedback fanout learning
WillTaylor22 May 26, 2026
f5a51c4
Merge remote-tracking branch 'origin/main' into claude/memory-review-…
WillTaylor22 May 26, 2026
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1 change: 1 addition & 0 deletions .claude/memory/MEMORY.md
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Expand Up @@ -10,6 +10,7 @@ Keep this file under 200 lines — anything longer is content bloat, not memory.
- [learnings/github-mcp-strips-html-comments](learnings/2026-05-26-github-mcp-strips-html-comments.md) — `update_pull_request` silently strips `<!-- ... -->` from PR bodies; session-id marker can't be set by agent (ENG-25)
- [learnings/recheck-open-prs-at-pr-open](learnings/2026-05-26-recheck-open-prs-at-pr-open.md) — session-start grep is insufficient; re-grep `list_pull_requests` right before `create_pull_request` to catch parallel-session races (PR #18 vs #20 ENG-25)
- [learnings/closed-pr-receives-review-after-close](learnings/2026-05-26-closed-pr-receives-review-after-close.md) — Closed PR can still get a REQUEST_CHANGES review seconds after dup-close; don't reopen, surface to sibling PR + Linear (PR #18 vs #20 ENG-25 race)
- [learnings/review-feedback-fanout](learnings/2026-05-26-review-feedback-fanout.md) — multiple REQUEST_CHANGES comments fire multiple manager sessions; fetch + check head-branch commits newer than the reviewer comment before doing work (PR #20)

## Decisions
- [decisions/mcp-for-small-writes-checkout-for-big](decisions/2026-05-26-mcp-for-small-writes-checkout-for-big.md) — Single-file writes go through GitHub MCP; multi-file or test-needing changes use the mounted checkout + `git push`
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31 changes: 31 additions & 0 deletions .claude/memory/learnings/2026-05-26-review-feedback-fanout.md
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# Review-feedback fanout: re-check the head branch before doing work

When the reviewer agent leaves *two* `AGENT_REVIEW: REQUEST_CHANGES`
comments seconds apart (e.g. its own webhook fanout, or a manual
re-review after edit), `/api/github-webhook` fires a fresh manager
session per comment. Each session is told "address the feedback on
the same branch, commit, push" — so two parallel sessions race to
produce the same fix.

PR #20 hit this. Two sessions, both extracted `extractSessionId` into
a module, both swapped `match` for `matchAll` + last-match, both added
a ~12-case unit harness, both widened the playwright config. The
first to push won. The second discovered the race on `git push --
rejected` and had to `git reset --hard origin/<branch>`.

Mitigation at the agent level (until the webhook itself dedupes):
before branching/editing for review feedback, run
`git fetch origin <head>` then
`git log --since="<reviewer comment created_at>" origin/<head>` — if
a commit newer than the reviewer comment already addresses the
feedback, stand down with a Linear comment.

Related: `conventions/check-open-pr-before-ticket-pickup.md` (analog
at ticket-pickup time, PR #15 vs #16) and
`learnings/2026-05-26-recheck-open-prs-at-pr-open.md` (analog at PR-
open time, PR #18 vs #20). Same race pattern, three webhook trigger
points.

Cleaner fix lives in the webhook: dedupe by `(pr_number, head_sha,
comment.first_line)` and refuse to spawn a duplicate manager
session within N seconds. Tracked separately — out of scope here.