fix(ci): stop Mergify label events from cancelling required PR Gate runs

[alchemydc]

Motivation

Mergify merge-queue requeues currently fail systematically. On every requeue, Mergify flips labels on the source PR (queued added, then the stale dequeued label removed ~40 s later). pr-gate.yml triggers on labeled/unlabeled and uses a single concurrency group with cancel-in-progress: true, so the second label event cancels the first PR Gate run mid-flight. The cancelled run's pr-gate-result aggregator still executes (if: always()) and posts a failure check on the PR head. Mergify's stay-in-queue condition check-success=pr-gate-result then dequeues the PR within ~2 minutes, before the queue draft's CI (which is green) can complete.

Observed on #11146: queue attempts on 2026-07-31 at 14:42 and 18:12 UTC were both dequeued "with no time running CI". The pr-gate-result check-run history on head 2c187ad6 shows failures at 14:43:28, 14:45:41, 18:14:19, and 18:15:56 — each seconds after a queued/dequeued label event — recovering to success once the label churn settles. The first queue attempt (2026-07-30) survived because no stale dequeued label existed yet, so only one label event fired.

tests-unit.yml already guards against this exact hazard ("Unrelated label events use a separate group so they cannot cancel the required unit test run"). lint.yml and test-crates.yml use the default pull_request types and are not exposed.

Solution

Mirror the tests-unit.yml pattern in pr-gate.yml, extended to cover unlabeled (PR Gate subscribes to both label event types; the only label the gate actually reacts to is A-release):

• Concurrency group: unrelated label events get an ignored-label group suffix so they cannot cancel the required run; all other events (including A-release label changes) stay in the required group.
• changes job: skips on unrelated label events, so semver-checks and changelog-gate skip too (this also stops re-running a full semver-checks pass on every label flip).
• release-readiness job: same guard, so a Mergify label flip on a release PR (which carries A-release) doesn't spawn a redundant readiness run. Adding/removing A-release still re-evaluates readiness in the required group.
• pr-gate-result job: skips on unrelated label events and gets a dynamic name (mirroring the unit-tests aggregator) so the skipped run's check posts under a different name and cannot replace the required pr-gate-result check that Mergify and branch protection consume.

Net effect on a Mergify requeue: both label events land in the ignored-label group, every job skips, the run completes in seconds, no check named pr-gate-result is posted, and the latest required-gate result on the head is untouched.

Tests

• YAML validated locally; expression constructs (group suffix, guard, dynamic aggregator name) are copied from the battle-tested tests-unit.yml pattern.
• On this PR (workflows run from the PR head for pull_request events): applying/removing an arbitrary label should produce a fast skipped run under the alternate check name, without cancelling the required PR Gate run or perturbing pr-gate-result.
• End-to-end after merge: requeue fix(state): make read_only_open_with_ephemeral_config_returns_error more robust #11146 (it still carries the stale dequeued label, so the failure scenario replays exactly) and confirm it survives past the ~2-minute mark.

Specifications & References

• Dequeue evidence: fix(state): make read_only_open_with_ephemeral_config_returns_error more robust #11146 Mergify status comments (attempts at 2026-07-31 14:42 and 18:12 UTC, drafts merge queue: checking main (25d0c1b) and #11146 together #11160/merge queue: checking main (fa10763) and #11146 together #11163, both "no time running CI" while the drafts' own pr-gate-result was green).
• Existing guard pattern: .github/workflows/tests-unit.yml concurrency group and unit-tests aggregator.

Follow-up Work

• Rapid edited events (Mergify editing queue-draft bodies) can still race-cancel a gate run on queue drafts; the window is ~25 s and it was not the cause of the observed dequeues. Can be addressed separately if it ever bites.

AI Disclosure

• AI tools were used: Claude Code for the CI-failure investigation and the workflow change; reviewed and tested by the author.

PR Checklist

• The PR title follows conventional commits format: type(scope): description
• The PR follows the contribution guidelines.
• This change was discussed in an issue or with the team beforehand.
• The solution is tested.
• The documentation and changelogs are up to date.

[Copilot]

Pull request overview

Prevents unrelated Mergify label events from cancelling required PR Gate runs.

Changes:

• Isolates unrelated label events into a separate concurrency group.
• Skips gate jobs and uses an alternate check name for those events.
• Preserves A-release label behavior.

[mergify]

Merge Queue Status

• ✅ Entered queue — 2026-07-31 21:12 UTC · Rule: batched · triggered by rule move to any queue if GitHub Rulesets are satisfied
• ✅ Checks skipped · PR is already up-to-date
• ✅ Merged — 2026-07-31 21:13 UTC · at 56741151ddb82956104f677fa96bf06963adc9ba · merge

This pull request spent 57 seconds in the queue, including 12 seconds running CI.

Required conditions to merge

• #review-threads-unresolved = 0 [🛡 GitHub repository ruleset rule PR Requirements]
  • fix(ci): stop Mergify label events from cancelling required PR Gate runs #11164
• github-review-approved [🛡 GitHub branch protection]
  • fix(ci): stop Mergify label events from cancelling required PR Gate runs #11164
• github-review-approved [🛡 GitHub repository ruleset rule PR Requirements]
  • fix(ci): stop Mergify label events from cancelling required PR Gate runs #11164
• any of [🛡 GitHub repository ruleset rule PR Requirements]:
  • check-success = @github-actions/lint
  • check-neutral = @github-actions/lint
  • check-skipped = @github-actions/lint
• any of [🛡 GitHub repository ruleset rule PR Requirements]:
  • check-success = test-crates
  • check-neutral = test-crates
  • check-skipped = test-crates
• any of [🛡 GitHub repository ruleset rule PR Requirements]:
  • check-success = unit-tests
  • check-neutral = unit-tests
  • check-skipped = unit-tests