ci: run CI in a merge queue so promotions stop deferring forever - #978
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Merges arrive faster than CI completes, so the deploy job's staleness gate defers to a newer commit that then defers itself. Tonight that ran five rounds and production never advanced past the pre-#963 build. A merge queue serialises main so each candidate gets a clean window. GitHub runs queue candidates on the merge_group event. Three things are needed before the queue can be turned on — enabling it first would hang every merge on a required check that never runs: - trigger CI on merge_group; - scope a candidate from the merge group's base/head range, so queued runs stay as narrow as pull requests instead of running the full matrix; - report `CI — required` on merge_group. It is the only required status context, and the queue waits on it per candidate. The 18 verification jobs need no change: they already fall through to the ci-scope outputs whenever the event is not `push`. The deploy jobs need none either — they additionally require github.ref == 'refs/heads/main', and a candidate builds on gh-readonly-queue/*, so a queued candidate cannot promote. Both properties are now pinned by tests. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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Why
Merges arrive faster than CI completes (~25 min apart vs ~30 min runs), so the deploy job's staleness gate defers to a newer commit — which then defers itself. Tonight that ran five rounds and production never advanced past the pre-#963 build. The gate is correct in isolation; it just has no way to eventually win.
A merge queue serialises
mainso each candidate gets a clean window.What this changes
GitHub runs queue candidates on the
merge_groupevent. Three things are required:merge_group.CI — requiredonmerge_group. It is the only required status context and the queue waits on it per candidate — this is the one that would hang merges if missed.What deliberately does not change
github.event_name == 'push' || needs.ci-scope.outputs.X, so onmerge_groupthey fall through to the scope outputs and behave exactly as they do on a PR.github.ref == 'refs/heads/main', and a candidate builds onrefs/heads/gh-readonly-queue/*. A queued candidate therefore cannot promote to production. This is the safety-critical property, and it is now pinned by a test rather than left implicit.Verification
ci-workflow.spec.mjs: 36/36, including three new guards — themerge_grouptrigger exists, the required context reports there, and all four production jobs stay pinned torefs/heads/main.merge_grouptrigger fails a guard.CI — requiredif:assertion to the new expression rather than loosening it.After merging
Enable the merge queue on
mainin branch protection. Worth doing in the same sitting — the two halves are only useful together.🤖 Generated with Claude Code