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

⚙️ Run configuration

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

Review profile: CHILL

Plan: Pro

Run ID: 53308f4c-7419-4866-8bc4-8e85ef2ed301

📥 Commits

Reviewing files that changed from the base of the PR and between 5422beb and 06679a1.

📒 Files selected for processing (1)

• .github/mergify.yml

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📝 Walkthrough

Summary by CodeRabbit

• Chores
  • Updated PR validation configuration to support label-based exemptions for product ID format requirements while maintaining existing commit message formatting checks.

Walkthrough

The Mergify configuration rule that detects product T-ID format violations in commit messages is updated to add a label-based exemption. PRs labeled legacy now bypass the commit-message validation, while the PR title check and the pattern format requirement remain in place.

Changes

Mergify Configuration

Layer / File(s)	Summary
T-ID violation rule with label exemption .github/mergify.yml	The invalid-task-id rule now requires label!=legacy alongside the commit-message pattern mismatch condition, exempting legacy-labeled PRs from the T-ID format check while preserving title validation and commit format enforcement.

Possibly related PRs

• vyos/vyatta-biosdevname#23: Introduced the original T-ID violation rule that this PR extends with label-based exemption logic.

✨ Finishing Touches

✨ Simplify code

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

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