ci: Add title checker action

.github/workflows/title-checker.yml

@@ -0,0 +1,99 @@
+name: PR Title Checker
+
+on:
+  pull_request_target:
+    types: [opened, edited, reopened]
+
+jobs:
+  check-title:
+    runs-on: ubuntu-latest
+    permissions:
+      pull-requests: write
+    steps:
+      - name: Validate PR Title and Apply Labels
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const title = context.payload.pull_request.title;
+            const { owner, repo } = context.repo;
+            const pr_number = context.payload.pull_request.number;
+
+            const regex = /^([a-z-]+)(?:\(([^)]+)\))?(!?): ([A-Z].+)$/;
+            const match = title.match(regex);
+
+            if (!match) {
+              core.setFailed("PR title does not follow format: 'type(scope)!: description'");
+              return;
+            }
+
+            const [_, type, scope, breaking, __] = match;
+
+            const displayTitle = `${title} (#${pr_number})`;
+            const maxLength = 72;
+
+            if (displayTitle.length > maxLength) {
+              core.setFailed(
+                `PR title is too long by ${displayTitle.length-maxLength} characters.`
+              );
+              return;
+            }
+
+            const repoLabels = await github.rest.issues.listLabelsForRepo({
+              owner,
+              repo,
+              per_page: 100,
+            });
+
+            const labelNames = repoLabels.data.map(l => l.name);
+            const labelsToAdd = [];
+
+            const typeLabel = `cc: ${type}`;
+            if (!labelNames.includes(typeLabel)) {
+              core.setFailed(`Invalid type: "${type}". No label "${typeLabel}" found in repo.`);
+              return;
+            }
+            labelsToAdd.push(typeLabel);
+
+            if (scope) {
+              const scopeLabel = `package: ${scope}`;
+              if (!labelNames.includes(scopeLabel)) {
+                core.setFailed(`Invalid scope: "${scope}". No label "${scopeLabel}" found in repo.`);
+                return;
+              }
+              labelsToAdd.push(scopeLabel);
+            }
+
+            if (breaking === '!') {
+              if (!labelNames.includes('breaking-change')) {
+                core.setFailed('No "breaking-change" label found in repo.');
+                return;
+              }
+              labelsToAdd.push('breaking-change');
+            }
+
+            const prLabels = await github.rest.issues.listLabelsOnIssue({
+              owner,
+              repo,
+              issue_number: pr_number,
+              per_page: 100,
+            });
+            const managedPrefixes = ['cc: ', 'package: '];
+            const labelsToRemove = prLabels.data
+              .map(l => l.name)
+              .filter(n => managedPrefixes.some(p => n.startsWith(p)) || n === 'breaking-change');
+            for (const label of labelsToRemove) {
+              await github.rest.issues.removeLabel({
+                owner,
+                repo,
+                issue_number: pr_number,
+                name: label
+              });
+            }
+
+            await github.rest.issues.addLabels({
+              owner,
+              repo,
+              issue_number: pr_number,
+              labels: labelsToAdd
+            });
+            console.log(`Successfully added labels: ${labelsToAdd.join(', ')}`);