[leehack]

Summary

• Pin Chrome supervisor exit-code precedence: after a recovered browser-close stall, leftover owned processes or missing output EOF still exit 125.
• Pin that ci.yml keeps the 30 s --post-done-seconds default (no workflow passes the flag; the script default is asserted).
• A stale reporter file now prints ::error::Stale reporter file <path> ... to stderr (still exit 125, no command started, no diagnostics dir).
• Make the post-done wait mutation deterministic: a CLI that exits by itself inside the window keeps its real exit, and recovery is asserted to happen at least post_done after reporter_done.

Refs #1837

Production-readiness scope

• User-facing scope: None; CI-only supervisor tests and one CI diagnostic message.
• Supported platforms/paths: Linux CI (tool/ci/supervise_chrome_test.py, test/ci).
• Unsupported or intentionally unavailable paths: Stale reporter file exits 125 with an ::error:: message naming the file.
• Out of scope / follow-ups: Writing a diagnostics dir/result.json for the stale-reporter case (the existing test pins that no directory is created); other #1837 items.

Completeness checklist

• Declared scope is fully implemented, or explicitly reduced above.
• Unsupported platform/option combinations fail loudly with actionable diagnostics or are clearly documented as unavailable.
• Public API docs, README/website docs, examples, support matrices, and changelog entries are updated where relevant. N/A: CI-only, no changelog.
• Regression coverage covers the original issue plus key negative/version-skew paths where relevant.
• Public capability changes update the validation coverage registry. N/A: no public capability change.
• Security/privacy review completed: the new message names only the reporter path the caller passed.
• Follow-up work is tracked in GitHub Issues, or explicitly marked "None" above.

PR type guidance

• Bugfix PR: root cause for (c): the supervisor's catch-all returned 125 silently. (d) was killed only by a race (2/6); now 5/5. Affected platform: Linux CI.

Test Plan

• dart run tool/prepare_workspace.dart
• dart format --output=none --set-exit-if-changed .
• dart analyze
• dart test -p vm -j 1 --exclude-tags local-only N/A: only test/unit/tooling/chrome_test_supervisor_test.dart and ci_workflow_selection_test.dart run locally (pass); the rest is untouched.
• dart test -p chrome --exclude-tags local-only N/A: no Dart/web change.
• coverage-lib N/A: no lib/ change.
• python3 -m unittest discover -s test/ci on macOS (216 OK, 28 skipped) and in python:3.12-slim (216 OK).

Matrix Evidence

Matrix row	Scope covered	Platform / model / backend	Result	Evidence / notes
N/A	Supervisor fixtures	Linux container / no model	Pass	Mutation now - done_at >= post_done removed: killed 5/5 runs. Swapping recovered_exit before the 125 branch: killed (2 tests).

Review Notes

• Independent review status: audit at 9bb9dc7 found no P1; one P2 and two P3 fixed at f45fe0c (suite timeout 20 s to 60 s; survivors-only fixture, killed by dropping survivors; stale-reporter error written through non-blocking echo). Delta re-audit of f45fe0c found no P1; P2 (per-test timeout 90 s) and P3s (stderr blocking restore, non-UTF-8 path, full/broken-pipe tests) fixed at 73c66a0. Re-audit of that delta pending.
• CI status / head SHA: 73c66a0, see PR checks.

High-risk regression review

• Classification: high-risk (regressionPolicy)
• Implementation task: this PR (author leehack, implementation agent session)
• Independent blocking QA task: three fresh agent audits, not the author: 9bb9dc7 (no P1; P2/P3 fixed), f45fe0c (no P1; P2/P3 fixed), delta audit at exact head 73c66a0 against ec4bf4f (PASS, no P1/P2; remaining P3 tracked in 0.19.1 follow-ups from audits #1837)
• Exact head / current base: 73c66a0 / ec4bf4f
• Production-branch deletion, bypass, or miswire proof: tool/ci/supervise_chrome_test.py is covered by test/unit/tooling/chrome_test_supervisor_test.dart, which runs the Python suite; mutations (remove post-done wait, drop survivors, swap exit precedence, print instead of echo, drop blocking restore, plain encode) are each killed by named fixtures.
• Affected-family real-model/artifact evidence: N/A (CI tooling, no model path)
• Explicit unavailable-family or other N/A evidence: Readiness evidence at pr1840-readiness.json (scratchpad); tool/testing/high_risk_readiness.dart exits 2 (unverifiedPrerequisites, expected without external auditor authentication).
• Known PR-caused P1 regressions: 0
• Unresolved review threads: 0

[leehack]

Landed via batch integration PR #1843 (rebase merge), one commit per constituent.

[github-actions]

Chat app preview removed for leehack/llamadart-chat-pr-1840.