chore: retire Mergify-replaceable reusable workflows (T8937)

[andamasov]

Deletes 5 reusable workflows + labeler.yml from vyos/.github. The consumer fleet has been swept — Phase C (73 in-scope repos, tiered), the 2026-06-03 VN LTS sweep (10 PRs), and the 2026-06-09/10 final straggler sweep (6 PRs: vyos/vyatta-bash@rolling + 3 VN hotfix + 2 VN security branches, all merged). Final fail-closed probe across all branches of all 73 in-scope repos: zero non-exempt stragglers, zero probe failures (see Phorge T8937 for the full rollout + exemption record).

Functionality is preserved by central Mergify rules in vyos/mergify:

• Base-branch labeling → Label PR with <branch> (toggle rules)
• Author-assign → Auto-assign PR author
• Title/commit format → the per-product-repo invalid-task-id rule + central invalid-title/invalid-body protections (T8966)
• Backport label → Mergify backport command is native
• Rebase label → dropped (auto-update opt-in supersedes)

Preserved in this repo:

• check-pr-conflict.yml — final probe found 2 live consumers (vyos/vyos-documentation current + heads/rolling); deletion deferred to a follow-up after those callers are retired.
• check-pr-merge-conflict.yml (T8934 committed-marker case Mergify cannot replicate)
• check-stale.yml (PR + issue stale stays in GHA per spec §2)

PR stale + issue stale stay in check-stale.yml (PR-stale migration deferred per spec §2).

The VyOS-Networks/.github twin PR follows; together they complete the rollout — central Mergify becomes the sole source of truth for fleet-wide PR automation.

Advances: T8937

🤖 Generated by robots

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

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

Review profile: CHILL

Plan: Pro

Run ID: 9e463778-7fb2-4eaa-bddc-a633b36ff9a0

📥 Commits

Reviewing files that changed from the base of the PR and between cb245fd and 06fb6bb.

📒 Files selected for processing (1)

• AGENTS.md

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📝 Walkthrough

Summary by CodeRabbit

• Chores
  • Removed repository-local automated workflows for pull request management (labeling, author assignment, rebase labeling, commit/PR message checks, and backport labeling).
• Documentation
  • Updated docs to note these protections and checks are now enforced centrally via Mergify rules rather than local workflows.

Walkthrough

This PR removes repo-local PR triage automation: five reusable workflows and the branch-based labeler; AGENTS.md is updated to reference central Mergify rules (see edited lines in AGENTS.md).

Files/lines cited: .github/labeler.yml (removed), .github/workflows/*.yml (removed), AGENTS.md (lines 29, 42-43).

Changes

GitHub automation removal

Layer / File(s)	Summary
Workflow and labeler deletions .github/labeler.yml, .github/workflows/add-pr-labels.yml, .github/workflows/add-rebase-label.yml, .github/workflows/assign-author.yml, .github/workflows/check-pr-message.yml, .github/workflows/label-backport.yml	Removed repo-local workflows that implemented PR triage: branch-based label mappings, PR label application, rebase detection, author assignment, PR title/message validation, and backport labeling.
Documentation update AGENTS.md (range_5f3850a44a54, range_7153bbc238c7)	Adjusted workflow listing and commit/PR title enforcement text to state checks are enforced by central vyos/mergify (edits at AGENTS.md lines 29 and 42-43).

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	Title precisely summarizes the main change: retiring five reusable workflows and labeler.yml, with reference to tracking issue T8937.
Description check	✅ Passed	Description comprehensively documents deletions, functionality preservation via Mergify, retained workflows, and rollout completion status.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch chore/T8937-retire-mergify-replaceable-reusables

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_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[andamasov]

Adversarial review — cb245fd (+ doc-fix 06fb6bb) — Codex + Gemini parallel

Both providers returned APPROVE.

1. [low][single-source: Codex] AGENTS.md:29 — still listed deleted workflows as present → fixed in 06fb6bb
2. [low][single-source: Codex] AGENTS.md:42 — title/commit enforcement still attributed to deleted check-pr-message.yml → fixed in 06fb6bb (now cites Mergify merge protections / T8966)
3. [low][single-source: Codex] AGENTS.md:43 — branch labeling still attributed to deleted add-pr-labels.yml → fixed in 06fb6bb

Gemini: NO FINDINGS. No critical issues from either provider. The doc-only fix commit 06fb6bb is covered by this review (it implements the findings above; no workflow-file delta).

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Each finding must receive a fix commit OR a pushback reply in a reply to this comment before merge. All three findings above are fixed by 06fb6bb. See /audit-pr-threads for resolution mechanics.