ci: move branch naming check from Mergify to GitHub Actions

[CatherineSue]

Description

Problem

Mergify's pull_request_rules creates a post_check status check on fork PRs even when the head-repo-full-name = lightseekorg/smg condition should exclude them. This produces noisy failing checks ("Rule: Enforce branch naming convention (internal) (post_check)") on external contributions.

Verified across 20 fork PRs — 3 had the spurious check (#1115, #1088, #1082), all with branch names that don't contain a /. The details_url on these checks points to the fork PR itself, confirming Mergify is directly evaluating the rule on forks (not SHA collision from another PR).

The head-repo-full-name condition correctly prevents the actions (close/comment) from firing on forks, but does not prevent the post_check from being created. This is Mergify's internal behavior and cannot be configured.

Additionally, the previously working merge_protections block (which used if guards to properly gate check creation) was removed by auto-generated PR #906 — Mergify's bot keeps opening PRs to "upgrade" the config and remove merge_protections, making it unsustainable to maintain.

Solution

• Remove the branch naming pull_request_rules entry from Mergify (eliminates post_check noise entirely)
• Add a branch-naming job to the existing pr-naming-check.yml GitHub Actions workflow
• The GHA job uses if: github.event.pull_request.head.repo.full_name == 'lightseekorg/smg' — completely invisible to fork PRs (no skipped check, no noise)
• On failure, the job posts a comment explaining the naming convention and auto-closes the PR (matching previous Mergify behavior)

Changes

• .github/mergify.yml — removed Enforce branch naming convention (internal) rule and stale auto-generated comment
• .github/workflows/pr-naming-check.yml — added branch-naming job with validation, comment, and auto-close

Test Plan

1. Internal PR with good branch name (e.g. feat/something): branch-naming job should pass
2. Internal PR with bad branch name (e.g. something): job should fail, post comment, and auto-close the PR
3. Fork PR (any branch name): branch-naming job should not appear at all in checks — no "Skipped", no noise
4. Verify existing pr-validation job (PR title + commit message checks) still works unchanged

To test, push a branch with a bad name from the internal repo:

git checkout -b test-bad-branch-name origin/main
git commit --allow-empty -s -m "test: verify branch naming auto-close"
git push -u origin test-bad-branch-name
# open PR, observe it gets commented on and closed
# then delete the branch
git push origin --delete test-bad-branch-name

Checklist

• cargo +nightly fmt passes (no Rust changes)
• cargo clippy --all-targets --all-features -- -D warnings passes (no Rust changes)
• (Optional) Documentation updated
• (Optional) Please join us on Slack #sig-smg to discuss, review, and merge PRs

Summary by CodeRabbit

• Chores
  • Migrated branch naming convention enforcement from Mergify to GitHub Actions for improved validation workflow consistency.

[coderabbitai]

Caution

Review failed

Pull request was closed or merged during review

📝 Walkthrough

Walkthrough

Branch naming convention enforcement is migrated from Mergify to GitHub Actions. The Mergify rule that validated branch names and closed non-conforming PRs is removed, replaced by a new Actions workflow job that validates branch names, comments with remediation guidance, and auto-closes failing PRs.

Changes

Cohort / File(s)	Summary
Mergify rule removal .github/mergify.yml	Removed the "Enforce branch naming convention (internal)" pull request rule, including its branch-name regex validation and auto-close/comment actions.
GitHub Actions job addition .github/workflows/pr-naming-check.yml	Added new branch-naming job that validates branch names against a lowercase/digits regex for internal PRs, comments with remediation commands, and auto-closes non-conforming PRs via GitHub CLI.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• ci(mergify): enable auto-close for non-conforming branch names #454: Re-enables the Mergify auto-close action that this PR removes, creating a direct conflict in enforcement behavior.
• ci(mergify): allow multi-segment branch names for dependabot #456: Updates the Mergify branch-naming rule regex to allow multi-segment names, modifying the exact rule being removed here.
• ci: temporarily disable auto-close for branch naming violations #426: Disables the auto-close action on the same Mergify branch-naming rule that this PR completely removes.

Suggested labels

ci

Suggested reviewers

• slin1237
• key4ng
• XinyueZhang369

Poem

🐰 A branch must be named just so,
No more Mergify's oversight,
Actions now keep the flow,
With comments of gentle might,
Lowercase and digits bright! ✨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately and specifically describes the main change: moving the branch naming check from Mergify to GitHub Actions, which is the primary objective of this pull request.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch ci/replace-mergify-branch-check

---

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

[claude]

Clean migration from Mergify to GitHub Actions. User-controlled inputs are properly env-var gated (no script injection), regex is unchanged, fork PRs are fully invisible, and comment+close behavior matches the previous Mergify rule.

[chatgpt-codex-connector]

💡 Codex Review

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[chatgpt-codex-connector]

Prevent fork PR check noise at workflow trigger level

Using a job-level if here does not make the check invisible on fork PRs: the workflow still runs on every pull_request, and branch-naming becomes a skipped check run rather than disappearing. GitHub documents that skipped jobs are reported as successful status checks, so this still adds check noise on forks and does not achieve the stated “no skipped check” behavior.

Useful? React with 👍 / 👎.

[gemini-code-assist]

Code Review

This pull request removes the Mergify rule that enforced branch naming conventions for internal branches, including the associated auto-close and commenting actions. I have no feedback to provide as there were no review comments.