ci: Reverse title-checker logic to format-title from labels (#590)

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: PierreQuinton

.github/workflows/title-checker.yml

@@ -0,0 +1,78 @@
+name: PR Title Formatter
+
+on:
+  pull_request_target:
+    types: [opened, edited, reopened, labeled, unlabeled]
+
+jobs:
+  format-title:
+    runs-on: ubuntu-latest
+    permissions:
+      pull-requests: write
+    steps:
+      - name: Format PR Title from Labels
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const { owner, repo } = context.repo;
+            const pr_number = context.payload.pull_request.number;
+            const rawTitle = context.payload.pull_request.title;
+
+            // Step 1: Strip any existing CC prefix to get the bare description.
+            const ccRegex = /^[a-z-]+(?:\([^)]+\))?!?: (.+)$/;
+            const ccMatch = rawTitle.match(ccRegex);
+            let description = ccMatch ? ccMatch[1] : rawTitle;
+
+            // Step 2: Capitalize first letter.
+            description = description.charAt(0).toUpperCase() + description.slice(1);
+
+            // Step 3: Read PR labels and require exactly one "cc: <type>" label.
+            const prLabels = await github.rest.issues.listLabelsOnIssue({
+              owner,
+              repo,
+              issue_number: pr_number,
+              per_page: 100,
+            });
+            const labelNames = prLabels.data.map(l => l.name);
+
+            const ccLabels = labelNames.filter(n => n.startsWith('cc: '));
+            if (ccLabels.length === 0) {
+              core.setFailed('No "cc: <type>" label found on this PR. Please add exactly one.');
+              return;
+            }
+            if (ccLabels.length > 1) {
+              core.setFailed(`Multiple "cc: <type>" labels found: ${ccLabels.join(', ')}. Please keep exactly one.`);
+              return;
+            }
+            const type = ccLabels[0].slice(4);
+
+            // Step 4: Use scope from "package: <name>" label if exactly one is present.
+            const packageLabels = labelNames.filter(n => n.startsWith('package: '));
+            const scope = packageLabels.length === 1 ? packageLabels[0].slice(9) : null;
+
+            // Step 5: Check for breaking-change label.
+            const isBreaking = labelNames.includes('breaking-change');
+
+            // Step 6: Build new title.
+            let newTitle = type;
+            if (scope) newTitle += `(${scope})`;
+            if (isBreaking) newTitle += '!';
+            newTitle += `: ${description}`;
+
+            // Step 7: Enforce 72-character limit (counting the trailing " (#NNN)").
+            const displayTitle = `${newTitle} (#${pr_number})`;
+            if (displayTitle.length > 72) {
+              core.setFailed(
+                `Formatted title is too long by ${displayTitle.length - 72} characters: "${displayTitle}"`
+              );
+              return;
+            }
+
+            // Step 8: Update the PR title.
+            await github.rest.pulls.update({
+              owner,
+              repo,
+              pull_number: pr_number,
+              title: newTitle,
+            });
+            console.log(`PR title updated to: "${newTitle}"`);