test(parity): classify stalled gap fixtures as timeouts

[proggeramlug]

Fixes #10720.

The thread-release fixture now waits for the thread count to return to its expected range. The stdin-backpressure fixture waits for the marker without turning a local deadline into a no-marker result, and no longer prints a fixture-watchdog result when a child stalls. The parity harness's existing timeout reports these failures as timeouts instead of output mismatches.

Verification:

• node --experimental-strip-types test-files/test_gap_9592_child_timeout_threads.ts on macOS
• The same fixture with Node 26 on Linux (perrymaster), exercising the /proc/self/task branch
• node --experimental-strip-types test-files/test_gap_9493_child_stdin_backpressure.ts on macOS
• git diff --check

Summary by CodeRabbit

• Bug Fixes

  • Improved diagnostic accuracy for stalled thread-release and stdin-backpressure scenarios.
  • These cases are now reported as timeouts instead of parity mismatches caused by local deadlines.
  • Updated test behavior to wait for expected process and thread completion, reducing misleading failure results.

• Documentation

  • Added a changelog entry describing the updated timeout reporting behavior.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Advanced

Run ID: 4dddcad2-36e7-4af0-bf88-62c0a5d59848

📥 Commits

Reviewing files that changed from the base of the PR and between c1569e2 and 01267ee.

📒 Files selected for processing (3)

• changelog.d/10985-parity-fixture-timeouts.md
• test-files/test_gap_9493_child_stdin_backpressure.ts
• test-files/test_gap_9592_child_timeout_threads.ts

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📝 Walkthrough

Walkthrough

The two parity fixtures no longer use local deadlines to produce boolean results. They wait for completion conditions and let the parity harness classify stalled execution as a timeout.

Changes

Parity fixture timeout handling

Layer / File(s)	Summary
Stdin backpressure marker wait test-files/test_gap_9493_child_stdin_backpressure.ts, changelog.d/10985-parity-fixture-timeouts.md	The fixture removes its watchdog and waits unconditionally for the marker. The changelog documents the timeout classification.
Timeout thread release wait test-files/test_gap_9592_child_timeout_threads.ts	The Linux fixture waits until timeout threads are released and then prints timeout threads released: true.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix · Severity of issue fixed: Medium

Merge Risk: ⚪ Minimal · up to 01267

The fixtures classify stalled behavior as timeouts instead of false output mismatches, with no actionable merge-blocking risk remaining.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the test change and the new timeout classification for stalled gap fixtures.
Description check	✅ Passed	The description explains the purpose, lists the fixture changes, references issue #10720, and provides concrete macOS and Linux verification steps. It is sufficiently complete despite not reproducing …
Linked Issues check	✅ Passed	Issue #10720 requires both fixtures to avoid local wall-clock results and let the parity harness classify stalls as timeouts. In test_gap_9592_child_timeout_threads.ts, the Linux path now waits unti…
Out of Scope Changes check	✅ Passed	The reviewed changes are limited to the two fixtures named by issue #10720 and a changelog entry that documents their timeout classification. The removed watchdog result, marker wait changes, and thre…
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 2…

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[proggeramlug]

Landed on main in merge train 257 (#11039, v0.5.1640), main 990b3eeada.

Carried at head 01267ee777. CI on the train head passed every job except the known public-baseline lint step: all 6 gap shards, cargo-test, e2e-scoped, gc-stress, check, warnings and security-audit green.

This train was split by blast radius after an earlier 35-PR assembly hit five gap regressions: it carries only PRs touching no lowering path. Trains rebase-merge, so commits get new SHAs and GitHub cannot mark this merged. Closed as landed.