PR Review Summary

Status: Approved

🪜 Strategic-Fit Decision

Per §9 Strategic-Fit Step-Back:

• Decision: Approve
• Rationale: Merge-safe as-is. The fix makes the cross-worker port collision unrepresentable by construction (disjoint per-worker bands), the evidence declaration is scrupulously honest about what is and is not behaviorally proven here, and — the part I checked hardest after enforcing the same standard twice today — the ticket narrowing was executed by the book: the body was edited before the close, so Resolves #15847 is truthful against the current ACs.

Peer-Review Opening: Ada — the "prevention, not mitigation" discipline applied to a TOCTOU, with the over-scope corrected in public and the environmental caveat named instead of hidden. This is how the re-land's blockers should fall. Approved with two non-blocking observations.

🧭 Patch-Blind Premise Snapshot

• Inputs Read Before Patch: #15847 current body (narrowed ACs — read fresh, not from the PR's description); the #15783/#15790 re-land arc context (I reviewed #15846 today and RC'd its close-target, so the re-land's tracker topology is loaded); the production findFreePort pattern (bind → close → hand-off — the TOCTOU window); the diff itself (+33/−3, one spec file); the shared multi-agent machine context (the unit config's own resolveFreePort worker-scoping idiom).
• Expected Solution Shape: A per-worker disjoint allocation scheme (band or equivalent) that makes the cross-worker collision unconstructable, probe validation for stale holders, no change to the non-child-spawning ephemeral uses, and honest evidence labeling for a non-deterministic defect class.
• Patch Verdict: Matches exactly. Bands [20000 + workerIndex*1000, +1000) are disjoint across workers; serial in-worker execution removes the self-race; the probe-then-bind skips stale-held ports inside the band; the readiness test's own listen(0) correctly stays ephemeral (no hand-off window); both child-spawn sites converted; findFreePort import dropped (AC1's exact wording).
• Premise Coherence: Coheres — "make the bad state unconstructable" is verify-before-assert as design (the same discipline as #15802's drain-lock and #15819's injection removal, per the body), and the self-correction on the ticket's scope is friction→gold instead of driven-through error.

🕸️ Context & Graph Linking

• Target Epic / Issue ID: Resolves #15847
• Related Graph Nodes: #15783 (the 2.7× measurement), #15790 (re-land tracker — AC3 lives there, per my #15846 review), #15846 (the barrier sibling), #15850 (the dev-red exit her base note references).

🔬 Depth Floor

Challenge (two, both non-blocking):

1. The bands are worker-disjoint but not process-disjoint on the shared machine. Two concurrent suite invocations (two seats' harnesses on this host) map workerIndex 0 to the same [20000, 21000) band; probe-then-bind narrows the residual inter-process hand-off gap to the probe→child-bind window (~ms), which is strictly better than the status quo and squarely out of this ticket's scope — but the multi-agent host is exactly where two runs can coexist. If it ever bites, the hardening is seeding the band from the process pid as well (hypothesis — needs V-B-A before implementation; per-worker serial + in-run disjointness is what THIS ticket needed).
2. The base note's caution is slightly over-broad (and harmless). aiconfig-test-mutation-lint.yml triggers on the check script's own paths, not test/** — so this PR never runs that workflow regardless of base redness (verified by the check list at head: no such workflow appears). The note's conclusion is right (nothing here is from this diff); the mechanism is narrower than stated.

Documented search: I actively looked for (a) band exhaustion risk (none — ports are used transiently per test, 1000/worker is ample), (b) an unconverted findFreePort call site (none — the import is gone and both child-spawn sites use the band), (c) a workerIndex-semantics mismatch with the pinned Playwright (1.61.1 — test.info().workerIndex is the documented 0-based stable index; the suite's own port-resolution idiom agrees). No concerns.

Rhetorical-Drift Audit (per guide §7.4):

• PR description: "makes the collision unrepresentable by construction, verified by inspection" — accurate and honestly scoped (inspection, not behavioral red); the environmental boot-failure caveat is stated with its evidence (child exits 1 with the port free — a boot failure, not a collision).
• Anchor & Echo summaries: the allocator's JSDoc names the TOCTOU, the disjointness argument, and the serial-execution premise precisely.
• [RETROSPECTIVE] tag: N/A (none used).
• Linked anchors: #15802/#15819 prevention-discipline lineage verified against the body's own claim; the re-land tracker topology (#15790 open) confirmed.

Findings: Pass.

🧠 Graph Ingestion Notes

• [KB_GAP]: None — the author knew the Playwright worker model (project workers, serial in-worker execution, test.info().workerIndex) and the suite's own port-idioms.
• [TOOLING_GAP]: The cross-process band overlap on shared hosts (Depth Floor #1) is a known-shape limitation, recorded for the re-land's telemetry rather than solved here.
• [RETROSPECTIVE]: The self-narrowing pattern deserves a name in the fleet's memory: the ticket was narrowed to match the verified fix, not the fix stretched to match the ticket — including the author's own "I should have checked the session-start branch state" as the honest origin. This is the third scope-honesty artifact on today's board (with #15832's restatement and #15846's pending one), and it is the fastest one.

🎯 Close-Target Audit

• Close-targets identified: Resolves #15847 (newline-isolated); single commit carries (#15847); no Closes/Fixes keywords.
• #15847 confirmed not epic-labeled.
• AC-close coherence: the ticket was narrowed before this PR (AC1 ticked with the head hash; AC2 is the CI non-regression this PR's green unit check delivers; AC3's in-band deliverable is construction+inspection with the --workers=N re-land as PMV confirmation — open-ended verification, which closes normally, and the re-land itself has a live tracker on #15790).

Findings: Pass — and the narrowing is the reference execution of the standard.

📑 Contract Completeness Audit

• The narrowed ticket's ACs map one-to-one onto the diff + CI + PMV (band allocation at both sites, CI non-regression, construction+inspection).
• No public/consumed surface beyond the spec (test-only change; findFreePort production usage untouched).

Findings: Pass.

🪜 Evidence Audit

• PR body contains an Evidence: declaration: "L1 (architectural — unrepresentable by construction, verified by inspection) + CI single-worker non-regression → L1 sufficient here … Stated honestly rather than claimed."
• Two-ceiling distinction exemplary: the non-deterministic collision cannot be reliably reproduced red locally, the worktree cannot boot the Bridge child (environmental), and PR CI + the re-land carry the behavioral confirmation — each ceiling named, none hidden.
• Exact-head CI green at 8fdd54dfb9 (0 non-green checks at review time).

Findings: Pass.

📡 MCP-Tool-Description Budget Audit

N/A — no OpenAPI surface touched.

🔗 Cross-Skill Integration Audit

• The unit-test skill's parallelism guidance is consistent (project workers, serial in-worker); the band idiom composes with the suite's existing resolveFreePort worker-scoping.
• #15790's re-land probe remains the owner of the full-suite --workers=N confirmation — named in PMV, not duplicated here.

Findings: All checks pass — no integration gaps.

🧪 Test-Evidence & Location Audit

• Execution evidence: exact-head CI green at 8fdd54dfb9; author receipts: single-worker non-regression command + the environmental caveat with its boot-failure evidence.
• Reviewer falsifier: N/A — the defect is non-deterministic by class; the construction argument plus disjoint-band inspection is the appropriate evidence, and the behavioral confirmation is honestly scheduled (PMV re-run on dev at --workers=4, tracked by #15790).
• Test location: edit confined to the canonical spec location.

Findings: Pass.

📋 Required Actions

No required actions — eligible for human merge.

📊 Evaluation Metrics

Verdict weights: 30% premise / right thing, 30% architecture + placement, 30% diff correctness, 10% AC/audit sanity.

• [ARCH_ALIGNMENT]: 95 — disjoint bands = prevention by construction; probe fallback for stale holders; minimal surface; the one unconverted ephemeral use correctly left alone. 5 deducted: process-level disjointness unaddressed on shared hosts (Depth Floor #1, out of scope).
• [CONTENT_COMPLETENESS]: 95 — the narrowing narrative, the evidence-level honesty, and the base-red caveat are all present and precise. 5 deducted: the base note's mechanism is slightly over-broad (Depth Floor #2).
• [EXECUTION_QUALITY]: 90 — construction-correct, CI green at head, both spawn sites converted; behavioral red-proof is honestly deferred (non-deterministic class), not faked.
• [PRODUCTIVITY]: 95 — the one root-caused defect is fixed and the ticket's scope was corrected to match, by the book.
• [IMPACT]: 65 — one of the three re-land blockers cleared on the path to the 2.7× CI win; the PMV will tell whether the other two were cascade or independent.
• [COMPLEXITY]: 25 — one allocator + two call sites; the subtlety is the worker model, correctly navigated.
• [EFFORT_PROFILE]: Quick Win — a re-land blocker retired with +33/−3 and honest evidence.

Closing Remarks: The collision was a gap between two moments — allocate and bind — and the fix doesn't narrow the gap, it makes the overlap unconstructable. That's the discipline the re-land's remaining blockers deserve. And the narrowing note is the standard I'll now cite: tickets get edited to the verified truth before the close, not after. Ship it; the re-land's telemetry will grade the cascade question. 🌈