[FEATURE] Automatic commit message for pull request merge

[c-vigo]

Description

Merge commit should follow message standards, either via:

• Automatic web interface commit message upon pull request merge
• GH API

Problem Statement

Merge commits do not follow our commit standard

Proposed Solution

Example of message following our standards:

chore: merge pull request #78 from vig-os/feature/58-default-commit-validation

feat(vigutils): add --require-scope flag and strict-by-default hook config

Passes all CI/CD

Refs: #58

Alternatives Considered

No response

Additional Context

No response

Impact

No response

[gerchowl]

Implementation Plan

Issue: #79
Branch: feature/79-auto-merge-commit-message

Design Decisions (from brainstorm)

• Repo merge settings changed via gh api:
  • merge_commit_title: MERGE_MESSAGE → PR_TITLE (merge commit subject = PR title)
  • merge_commit_message: PR_TITLE → PR_BODY (merge commit body = PR body)
• PR titles already follow the commit message standard (type(scope): description), so the merge commit subject is automatically compliant.
• PR body template updated to include Refs: line, ensuring traceability in merge commit body.
• PR title validated by a CI workflow that reuses validate_commit_msg.py (existing logic, no duplication).

Tasks

• Task 1: Add gh-repo-merge-settings recipe to justfile.gh — sets merge_commit_title=PR_TITLE and merge_commit_message=PR_BODY via gh api — justfile.gh — verify: recipe parses (just --list --justfile justfile.gh)
• Task 2: Write failing test for PR title validation (test that validate_commit_message correctly validates a PR-title-only string with refs exemption) — packages/vig-utils/tests/ — verify: uv run pytest shows test failing
• Task 3: Add CLI support for subject-only validation (all refs optional) to validate_commit_msg.py — packages/vig-utils/src/vig_utils/validate_commit_msg.py — verify: uv run pytest passes
• Task 4: Create pr-title-check.yml workflow that validates the PR title using validate-commit-msg on pull_request: opened/edited/synchronize — .github/workflows/pr-title-check.yml — verify: actionlint or yamllint passes
• Task 5: Update PR body template to include Refs: # at the bottom so merge commit body contains traceability — .github/pull_request_template.md — verify: visual inspection
• Task 6: Update CHANGELOG.md under ## Unreleased — CHANGELOG.md — verify: follows existing format

TDD applies to: Tasks 2–3 (test first, then implementation).
TDD skipped for: Tasks 1, 4, 5, 6 (config, workflow YAML, template, docs — not unit-testable).

cc @c-vigo — does this plan look good to you?

[c-vigo]

Looks good to me! COuple of points:

• You might need a placeholder for pr-title-check.yml in main for this to work right away, not sure.
• After implementing and merging, I would leave the issue open until we verify it and turn on Auto merge here. The gh-repo-merge-settings recipe should also set this value.

[gerchowl]

Implementation Plan

Issue: #79
Branch: feature/79-auto-merge-commit-message

Tasks

• Task 1: Create setup-gh-repo.sh script that configures repo merge settings (merge_commit_title=PR_TITLE, merge_commit_message=PR_BODY, allow_auto_merge=true) via gh api — assets/workspace/.devcontainer/scripts/setup-gh-repo.sh — verify: bash -n assets/workspace/.devcontainer/scripts/setup-gh-repo.sh
• Task 2: Wire setup-gh-repo.sh into post-create.sh — call it after git/gh setup — assets/workspace/.devcontainer/scripts/post-create.sh — verify: bash -n assets/workspace/.devcontainer/scripts/post-create.sh
• Task 3: Write failing test for --subject-only mode in validate_commit_msg.py (TDD red) — packages/vig-utils/tests/test_validate_commit_msg.py — verify: just test-vig-utils shows test failing
• Task 4: Implement --subject-only flag and subject_only parameter in validate_commit_message() (TDD green) — packages/vig-utils/src/vig_utils/validate_commit_msg.py — verify: just test-vig-utils passes
• Task 5: Create pr-title-check.yml workflow — validates PR title using validate-commit-msg --subject-only on pull_request: opened/edited/synchronize — .github/workflows/pr-title-check.yml — verify: yamllint .github/workflows/pr-title-check.yml
• Task 6: Update PR body template to include Refs: # placeholder — .github/pull_request_template.md — verify: visual inspection
• Task 7: Update CHANGELOG.md under ## Unreleased — CHANGELOG.md — verify: follows existing format

TDD applies to: Tasks 3–4 (test first, then implementation).
TDD skipped for: Tasks 1, 2, 5, 6, 7 (shell scripts, workflow YAML, template, docs — not unit-testable).

Post-merge action: Run setup-gh-repo.sh manually against vig-os/devcontainer since the container won't be recreated just for this change.