T8966: add legacy-label escape to invalid-task-id rule (commit check exempt)

[andamasov]

Adds a maintainer-controlled legacy label escape to the per-repo T-ID rule (toggles invalid-task-id). The PR title check stays enforced for every PR; the per-commit check is exempted when a PR carries the legacy label — an escape hatch for grandfathered PRs whose commit history cannot be rewritten (repos that squash-merge and block force-push). Pilot verified on vyos/vyos.vyos. Change-management: IS-539. Tracked under T8966.

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ℹ️ Recent review info

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Configuration used: Repository YAML (base), Central YAML (inherited), Organization UI (inherited)

Review profile: CHILL

Plan: Pro

Run ID: ae35e2f1-3657-4e3b-aeea-4be1ab815c2e

📥 Commits

Reviewing files that changed from the base of the PR and between 966bab9 and 70a1a99.

📒 Files selected for processing (1)

• .github/mergify.yml

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📝 Walkthrough

Summary by CodeRabbit

• Chores
  • Updated internal pull request validation automation to exclude legacy pull requests from commit message formatting checks.

Walkthrough

The PR modifies the Mergify automation rule in .github/mergify.yml to gate the T<digits>: task-ID commit-message validation. When a PR is labeled legacy, the commit-message regex check is bypassed. The validation pattern itself remains unchanged; only the conditional trigger is updated.

Changes

Mergify Commit-Message Rule Gating

Layer / File(s)	Summary
Commit-message validation gating by label .github/mergify.yml	Lines 40–42: An and block adds label!=legacy condition to gate the existing task-ID commit-message regex check, allowing legacy-labeled PRs to skip this validation.

Possibly related PRs

• vyos/vyatta-bash#39: Adds or modifies T<digits>: title/commit check gating via labels in the same Mergify rules.

✨ Finishing Touches

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch feat/T8966-legacy-escape

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