ci: add Conventional Commits enforcement for PR titles (#337)

* ci: add PR title lint for Conventional Commits

Adds a GitHub Action that validates PR titles follow the Conventional
Commits format (type(scope): description). Since this repo uses
squash-merge, the PR title becomes the commit message on main, which
release-please uses for changelog generation.

Prevents commits from being silently dropped from the changelog when
merged without a conventional prefix.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* docs: clarify PR title convention for release-please in AGENTS.md

Expand the commit message section to explain that PR titles are the
commit messages (squash-merge), that non-conforming titles are blocked
by CI and silently dropped from the changelog, and include a concrete
bad/good example to guide agents.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* ci: add PR template with Conventional Commits guidance

Adds a pull_request_template.md that reminds authors the PR title
becomes the changelog entry via release-please. Includes the format
spec, type→changelog mapping, and a bad/good example.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix(ci): replace third-party action with inline regex check

The pinned SHA for amannn/action-semantic-pull-request was not
resolvable. Replace with a zero-dependency bash regex check that
validates PR titles against the Conventional Commits pattern.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: jamesadevine

.github/pull_request_template.md

@@ -0,0 +1,26 @@
+<!--
+  ⚠️  PR TITLE = CHANGELOG ENTRY
+  This repo uses squash-merge, so your PR title becomes the commit on main.
+  release-please uses it for the changelog and version bump.
+
+  Format:  type(scope): description
+  Example: feat(compile): add S360 Breeze MCP as first-party tool
+
+  Types that appear in the changelog:
+    feat  → Features     (bumps minor version)
+    fix   → Bug Fixes    (bumps patch version)
+
+  Types that do NOT appear in the changelog (no version bump):
+    chore, docs, refactor, test, ci, perf, build
+
+  Bad:  "Allow workspace to target a repo alias"
+  Good: "feat(compile): allow workspace to target a repo alias"
+-->
+
+## Summary
+
+<!-- Brief description of what this PR does and why. -->
+
+## Test plan
+
+<!-- How was this tested? (cargo test, manual verification, etc.) -->

.github/workflows/pr-title-lint.yml

@@ -0,0 +1,35 @@
+name: PR Title Lint
+
+on:
+  pull_request:
+    types: [opened, edited, synchronize, reopened]
+
+permissions:
+  pull-requests: read
+
+jobs:
+  lint:
+    name: Validate Conventional Commit
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check PR title
+        env:
+          PR_TITLE: ${{ github.event.pull_request.title }}
+        run: |
+          # Conventional Commits: type(optional-scope): description
+          PATTERN='^(feat|fix|chore|docs|refactor|test|ci|perf|build|revert)(\([a-zA-Z0-9_-]+\))?!?: .+'
+          if echo "$PR_TITLE" | grep -qE "$PATTERN"; then
+            echo "✅ PR title follows Conventional Commits: $PR_TITLE"
+          else
+            echo "::error::PR title must follow Conventional Commits format: type(scope): description"
+            echo ""
+            echo "  Got:      $PR_TITLE"
+            echo "  Expected: type(scope): description"
+            echo ""
+            echo "  Valid types: feat, fix, chore, docs, refactor, test, ci, perf, build, revert"
+            echo "  Examples:"
+            echo "    feat(compile): add S360 Breeze MCP as first-party tool"
+            echo "    fix: gitattributes writer quote paths with spaces"
+            echo "    chore: update MCPG_VERSION to 0.3.0"
+            exit 1
+          fi

AGENTS.md

@@ -107,15 +107,23 @@ Alongside the correctly generated pipeline yaml, an agent file is generated from
 
 ## Development Guidelines
 
-### Commit Message Convention
+### Commit Message and PR Title Convention
 
-This project uses [Conventional Commits](https://www.conventionalcommits.org/) for automated releases via `release-please`. All commit messages **must** follow the format:
+This project uses [Conventional Commits](https://www.conventionalcommits.org/) for automated releases via `release-please`. **PR titles are the commit messages** — this repo uses squash-merge, so the PR title becomes the commit on `main`.
+
+All PR titles **must** follow the format:
 
 ```
 type(optional scope): description
 ```
 
-Common types: `feat`, `fix`, `chore`, `docs`, `refactor`, `test`, `ci`. Commits that don't follow this format will be ignored by release-please and won't trigger a release.
+Common types: `feat`, `fix`, `chore`, `docs`, `refactor`, `test`, `ci`. PRs with non-conforming titles will be blocked by CI and, if merged, will be silently dropped from the changelog.
+
+- **`feat`** — triggers a minor version bump and appears under "Features" in the changelog.
+- **`fix`** — triggers a patch version bump and appears under "Bug Fixes".
+- All other types (`chore`, `docs`, `refactor`, etc.) — no version bump, no changelog entry.
+
+A PR titled `Allow workspace to target a repo alias` will be **ignored** by release-please. The correct title is `feat(compile): allow workspace to target a repo alias`.
 
 ### Rust Code Style