[MarkusNeusinger]

Summary

• Root cause of the TestRender::test_a_launcher_that_outlives_its_kill_blocks_renders_until_it_exits flake (two CI failures on 2026-10-23, runs 39932413037 and 39940278486). The fake launcher execs the harness, so the process the test keeps alive is the harness and carries the run's RLIMIT_CPU, one second for a one-second job (wire.run_cpu_seconds). The harness start (matplotlib import, a fresh font cache per test) costs about 0.33 CPU s locally and roughly 2.4 times that on the CI runner (the plain render test takes 0.54 s here and 1.31 s there). Whenever it spent the full second, the kernel's SIGKILL ended the "stuck" launcher about 50 ms after the timeout, inside the 0.2 s grace window, so stuck read 0. The failing run's wall_s=1.054 is that death: a survivor keeps _stop waiting the full grace, about 1.22 s.
• The executor is correct; only the test raced. A real sandbox do runs on the host, outside the limit the harness sets inside the sandbox, and stuck counts only launchers still alive. The test now gives the run the host's full CPU cap and asserts that cap on the survivor with resource.prlimit, so it fails every time without the fix instead of once in a while.
• Takes ruff's PEP 758 except form in two lines from feat(core): adaptability checker for Python implementations #12244 that main's Lint job flags since the 3.14 move. These are the same hunks as fix(js-render): bump Playwright to 1.64.1 for the Ubuntu 26.04 runner #12259, so whichever PR lands first, the other merges cleanly.

Ruled out: the fake binary's delete --force only logs and exits 0. The sleeper writes nothing, so it gets no SIGPIPE. Asyncio cancellation of the readers does not close the transport, and PYTHONASYNCIODEBUG=1 with -X dev reports no "close running child" or unclosed-transport warning. Coverage does not follow subprocesses (pytest-cov 7, no patch = subprocess). Python 3.14 makes the harness start only about 5 % heavier than 3.13 (0.33 against 0.32 CPU s, same harness, same matplotlib), so it narrowed the margin but did not cause the flake.

Plan

N/A

Test plan

• Deterministic reproduction of the CI signature (assert (True and 0 == 1), wall_s about 1.02, launcher exit -9): the old test body with code that spends more than one CPU second before it sleeps.
• Adjusted test with the CPU-cap line removed: 31 of 31 failures, 16 idle and 15 under 48 busy loops on 32 threads.
• Adjusted test as committed: 50 of 50 passes, 25 idle and 25 under 48 busy loops.
• uv run pytest tests/unit tests/integration -n 4 --dist worksteal: 12,715 passed, 3 skipped.
• tests/unit/agents/renderer under python -X dev with PYTHONASYNCIODEBUG=1: 179 passed, no asyncio warnings.
• ruff check ., ruff format --check ., mypy api core agents and tools.changelog check --base origin/main are clean.

[Copilot]

🟢 Approval recommended

The reviewed changes have no unresolved blocking issues and the test stabilization is covered by the supplied validation.

No open issues 🎉

What changed in this PR

This pull request makes the stuck-launcher renderer test deterministic by preventing the fake survivor process from inheriting the job’s one-second CPU limit. It also updates the adaptability checker syntax for Python 3.14 and documents the fix.

Changes:

• Applies and verifies the configured CPU limit for the test survivor.
• Updates both adaptability checker copies to use PEP 758 exception syntax.
• Adds a changelog fragment for the test reliability fix.

File	Description
tests/​unit/​agents/​renderer/​test_executor.py	Makes the stuck-launcher test deterministic and verifies the survivor’s CPU limit.
core/​adaptability.py	Applies the Python 3.14-compatible exception syntax.
changelog.d/​executor-stuck-test.md	Documents the renderer test flake fix.
automation/​scripts/​adaptability_check.py	Keeps the generated checker mirror synchronized with the source checker.

_{Review effort: Lite}

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
automation/scripts/adaptability_check.py	0.00%	1 Missing ⚠️
core/adaptability.py	0.00%	1 Missing ⚠️

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