[leehack]

Summary

• Adds a supervisor test for the stale-reporter path with a non-blocking caller stderr, so restoring the wrong blocking mode no longer survives (Pin Chrome supervisor exit precedence and post-done wait (#1837 a-d) #1840 audit follow-up in 0.19.1 follow-ups from audits #1837).

Production-readiness scope

• User-facing scope: None; test-only.
• Supported platforms/paths: CI supervisor (tool/ci/supervise_chrome_test.py) on Linux.
• Unsupported or intentionally unavailable paths: N/A.
• Out of scope / follow-ups: None.

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. (N/A, test-only)
• Public API docs, README/website docs, examples, support matrices, and changelog entries are updated where relevant. (N/A, test-only)
• Regression coverage covers the original issue plus key negative/version-skew paths where relevant.
• Public capability changes update the validation coverage registry. (N/A)
• Security/privacy review completed: no secrets or paths leak.
• Follow-up work is tracked in GitHub Issues, or explicitly marked "None" above.

PR type guidance

• Bugfix PR: N/A, test-only; no production change.

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: Python-only change
• dart test -p chrome --exclude-tags local-only N/A: Python-only change
• coverage-lib N/A: no lib/ change
• python -m unittest test.ci.test_supervise_chrome_test in python:3.12-slim (git, jq installed): 39 tests OK

Matrix Evidence

Matrix row	Scope covered	Platform / model / backend	Result	Evidence / notes
N/A	Test-only Python CI change	python:3.12-slim	Pass	39 tests OK

Mutation check (tool/ci/supervise_chrome_test.py:430 os.set_blocking(2, blocking) -> os.set_blocking(2, True)): the new test_stale_reporter_error_keeps_a_non_blocking_caller_stderr_non_blocking fails (1 failure, all else pass); unmutated: OK.

Review Notes

• Independent review status: pending
• CI status / head SHA: pending

High-risk regression review

• Classification: standard
• Implementation task: N/A
• Independent blocking QA task: N/A
• Exact head / current base: N/A
• Production-branch deletion, bypass, or miswire proof: N/A
• Affected-family real-model/artifact evidence: N/A
• Explicit unavailable-family or other N/A evidence: N/A
• Known PR-caused P1 regressions: 0
• Unresolved review threads: 0

Refs #1837 #1845

[leehack]

Landed through the 0.19.2 batch integration PR #1870 (rebase merge, one commit per constituent; this PR's pinned head was audited/CI-gated there).

[github-actions]

Chat app preview removed for leehack/llamadart-chat-pr-1846.