msd-core/docs/how-to/read-ci-timeout-signals.md

How to read CI timeout budget signals

Every matrixed CI job (test, test-conformance in .github/workflows/test.yml; mutate in mutation.yml; smoke in install-smoke.yml) now reports how close it ran to its timeout-minutes cap. This page is for a maintainer trying to answer: is a lane drifting toward its cap, and where do I look? (test-conformance runs the platform-conformance-tier file list — scripts/lib/platform-conformance-tier.generated.cjs — on windows-latest, sharded three ways, and macos-latest, unsharded; it is the sole gating signal for real-OS coverage.)

1. A single run crossed 90% of its budget

Open the job's page in the Actions run — two places show it, both populated by the same computation (scripts/lib/ci-job-timing.cjs):

• The Checks tab annotation. A ::warning:: line renders as an expandable warning banner on the PR's Checks summary, naming the job, its elapsed time, its cap, and the percentage — visible without opening the job's logs.
• The job's step summary. The same information, as a Markdown line, appended to the job's own summary page ($GITHUB_STEP_SUMMARY) by that job's own "Check job budget (near-cap advisory)" step — always the job's last step.

Neither signal fails the job. A near-cap warning on an otherwise-green run means exactly what it says: this run finished, but with less margin than the headroom-factor gate assumes it has.

If the warning never appears even on a job that was actually cancelled at its cap, that is expected — a killed job never reaches its last step, so the in-job check never runs. See §2.

2. Checking the accumulated trend

.github/workflows/ci-timeout-report.yml runs daily (and on-demand via workflow_dispatch). It polls GitHub's Actions REST API directly — independent of whether any individual job's own near-cap step ran — so it also catches jobs that were actually cancelled by a timeout breach (GitHub's Jobs API still reports started_at/completed_at for a cancelled job).

Each run's new rows land in tests/ci-timeout-budget-history.jsonl, one JSON object per line:

{"runId":123456,"jobName":"test (ubuntu-latest, 24, shard 1/3)","workflowFile":"test.yml","sha":"...","completedAt":"...","elapsedMs":432000,"timeoutMinutes":15,"pct":0.8,"runEvent":"push"}

runEvent matters for install-smoke.yml's smoke job specifically — its pull_request runs use a smaller matrix (no macos-latest full_only row) than its push runs, so a pct figure only means the same thing across rows sharing the same runEvent.

Because next is a protected branch, the report never pushes directly to it — each scheduled run opens (or the prior run's already merged, in which case a fresh one opens) a small, data-only PR carrying just that run's new rows, titled chore: CI timeout budget report — run <id>. Merge these like any other PR; there is nothing to review beyond "did the numbers land."

3. A lane is repeatedly near-cap — what to do

Neither mechanism here decides what to do about a lane that's genuinely trending toward its cap. That is a maintainer call among three options, each with real tradeoffs:

• Raise the timeout-minutes cap for that job.
• Rebalance the shard split so no single shard carries a disproportionate share of the suite (see scripts/run-tests.cjs's selectShard, which packs shards by measured cost from tests/test-timings.json).
• Trim what runs on the long-pole shard — for the test job, shard 1 also carries the unsharded aux suites (integration/security/install/slow); moving one elsewhere changes what shard 1 costs.

tests/ci-test-job-timeout-budget.test.cjs will keep failing to accept a lowered timeout-minutes beneath 1.5x whatever LANE_COSTS/COVERED[*].timeoutMinutes records as that job's last measured cost — raising the cap back down is not something either mechanism will silently allow.