fix: ensure labels exist before creating regression issues (#1763)

The `needs-investigation` label doesn't exist in this repo, causing the
GitHub API to return 422 when the performance monitor tries to create
regression issues. Add a step to ensure both labels exist before issue
creation, and add error handling around the issue creation step itself.

Fixes #1759

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Mossaka

.github/workflows/performance-monitor.yml

@@ -88,6 +88,28 @@ jobs:
             "| \($r.metric) | \($r.mean)\($r.unit) | \($r.median)\($r.unit) | \($r.p95)\($r.unit) | \($r.p99)\($r.unit) | \($t.target // "N/A")\(if $t then $r.unit else "" end) | \($t.critical // "N/A")\(if $t then $r.unit else "" end) |"' \
             benchmark-results.json >> "$GITHUB_STEP_SUMMARY"
 
+      - name: Ensure labels exist
+        if: steps.check.outputs.regression_count != '0'
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const labels = [
+              { name: 'needs-investigation', color: 'e4e669', description: 'Requires further investigation' },
+              { name: 'performance', color: 'd4c5f9', description: 'Performance related' },
+            ];
+            for (const label of labels) {
+              try {
+                await github.rest.issues.createLabel({ owner: context.repo.owner, repo: context.repo.repo, ...label });
+                core.info(`Created label: ${label.name}`);
+              } catch (e) {
+                if (e.status === 422) {
+                  core.info(`Label already exists: ${label.name}`);
+                } else {
+                  throw e;
+                }
+              }
+            }
+
       - name: Create regression issue
         if: steps.check.outputs.regression_count != '0'
         uses: actions/github-script@v7
@@ -123,10 +145,15 @@ jobs:
               `</details>`,
             ].join('\n');
 
-            await github.rest.issues.create({
-              owner: context.repo.owner,
-              repo: context.repo.repo,
-              title: `Performance regression detected (${new Date().toISOString().split('T')[0]})`,
-              body,
-              labels: ['performance', 'needs-investigation'],
-            });
+            try {
+              const issue = await github.rest.issues.create({
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                title: `Performance regression detected (${new Date().toISOString().split('T')[0]})`,
+                body,
+                labels: ['performance', 'needs-investigation'],
+              });
+              core.info(`Created regression issue: ${issue.data.html_url}`);
+            } catch (error) {
+              core.setFailed(`Failed to create regression issue: ${error.message}`);
+            }