perf: prove fixed-width date formatting against protected base

.jules/bolt.md

@@ -4,3 +4,6 @@
 ## 2026-07-12 - Optimize renderTaskRow DOM allocations
 **Learning:** Caching unattached template nodes and instantiating them via `.cloneNode(false)` reduces DOM instantiation overhead in O(N) render loops significantly.
 **Action:** Apply this optimization to other hot-path rendering elements such as rows, cells, and stack containers.
+## 2026-08-25 - Benchmark fixed-width date formatting before accepting micro-optimizations
+**Learning:** Engine-internal explanations are not acceptance evidence. A fixed-width date formatter optimization must preserve every observable output while demonstrating a material median improvement against an immutable protected-base revision in the same browser/runtime.
+**Action:** Keep date-format micro-optimizations only when the protected Chromium A/B benchmark proves exact semantic parity across a leap-year date corpus and at least a 10% median improvement; otherwise prefer the clearer implementation.

app.js

@@ -2682,22 +2682,32 @@ function clamp(value, min, max) {
   return Math.min(max, Math.max(min, value));
 }
 
+// ⚡ Bolt Optimization: Use inline ternary operator instead of String.padStart()
+// to avoid unnecessary string object allocations and JS-to-C++ overhead in hot loops.
 function formatDateInput(date) {
   const year = date.getUTCFullYear();
-  const month = String(date.getUTCMonth() + 1).padStart(2, '0');
-  const day = String(date.getUTCDate()).padStart(2, '0');
+  const m = date.getUTCMonth() + 1;
+  const d = date.getUTCDate();
+  const month = m < 10 ? '0' + m : '' + m;
+  const day = d < 10 ? '0' + d : '' + d;
   return `${year}-${month}-${day}`;
 }
 
 function formatLocalDateInput(date) {
   const year = date.getFullYear();
-  const month = String(date.getMonth() + 1).padStart(2, '0');
-  const day = String(date.getDate()).padStart(2, '0');
+  const m = date.getMonth() + 1;
+  const d = date.getDate();
+  const month = m < 10 ? '0' + m : '' + m;
+  const day = d < 10 ? '0' + d : '' + d;
   return `${year}-${month}-${day}`;
 }
 
 function formatCompactDate(date) {
-  return `${date.getFullYear()}${String(date.getMonth() + 1).padStart(2, '0')}${String(date.getDate()).padStart(2, '0')}`;
+  const m = date.getMonth() + 1;
+  const d = date.getDate();
+  const month = m < 10 ? '0' + m : '' + m;
+  const day = d < 10 ? '0' + d : '' + d;
+  return `${date.getFullYear()}${month}${day}`;
 }
 
 function formatPercent(value, digits) {

package.json

@@ -13,12 +13,12 @@
     "coverage": "npm run test:coverage",
     "server": "node server/server.mjs",
     "test:api": "node tests/api/auth-secret.test.mjs && node tests/api/smoke.mjs && node tests/api/ratelimit.test.mjs && node tests/api/attachment-status.test.mjs && node tests/api/session-revocation.test.mjs && node tests/api/orchestrator-attribution.test.mjs",
-    "test:unit": "node tests/unit/opencode-config.test.mjs && node tests/unit/changelog-release-notes.test.mjs && node tests/unit/analytics.test.mjs && node tests/unit/cpm.test.mjs && node tests/unit/baseline-compare.test.mjs && node tests/unit/workload.test.mjs && node tests/unit/cost-evm.test.mjs && node tests/unit/msproject.test.mjs && node tests/unit/auth-password.test.mjs && node tests/unit/editor-unsaved.test.mjs && node tests/unit/static-coverage-evidence.test.mjs && node tests/unit/dep-types.test.mjs && node tests/unit/weekly-report.test.mjs && node tests/unit/clearfolio.test.mjs && node tests/unit/clearfolio-adapter-mock-hmac.test.mjs && node tests/unit/orchestrator.test.mjs && node tests/unit/orchestrator-coverage.test.mjs && node tests/unit/orchestrator-attribution.test.mjs && node tests/unit/sprint-stats.test.mjs && node tests/unit/burndown.test.mjs && node tests/unit/pm-analysis.test.mjs && node tests/unit/cloud-sync-security.test.mjs && node tests/unit/attachment-status.test.mjs && node tests/unit/clearfolio-status-signal.test.mjs && node tests/unit/coverage-script-contract.test.mjs && node tests/unit/toast-accessibility.test.mjs",
+    "test:unit": "node tests/unit/opencode-config.test.mjs && node tests/unit/changelog-release-notes.test.mjs && node tests/unit/analytics.test.mjs && node tests/unit/cpm.test.mjs && node tests/unit/baseline-compare.test.mjs && node tests/unit/workload.test.mjs && node tests/unit/cost-evm.test.mjs && node tests/unit/msproject.test.mjs && node tests/unit/auth-password.test.mjs && node tests/unit/editor-unsaved.test.mjs && node tests/unit/static-coverage-evidence.test.mjs && node tests/unit/dep-types.test.mjs && node tests/unit/weekly-report.test.mjs && node tests/unit/clearfolio.test.mjs && node tests/unit/clearfolio-adapter-mock-hmac.test.mjs && node tests/unit/orchestrator.test.mjs && node tests/unit/orchestrator-coverage.test.mjs && node tests/unit/orchestrator-attribution.test.mjs && node tests/unit/sprint-stats.test.mjs && node tests/unit/burndown.test.mjs && node tests/unit/pm-analysis.test.mjs && node tests/unit/cloud-sync-security.test.mjs && node tests/unit/attachment-status.test.mjs && node tests/unit/clearfolio-status-signal.test.mjs && node tests/unit/coverage-script-contract.test.mjs && node tests/unit/toast-accessibility.test.mjs && node tests/unit/date-format-benchmark-order.test.mjs",
     "test:coverage": "c8 --all --include=app.js --include=cloud-sync.js --include=scripts/ci/static_coverage_evidence.mjs --include=server/attachment_status.mjs --include=server/app.mjs --include=server/auth.mjs --include=server/clearfolio.mjs --include=server/orchestrator.mjs --reporter=json --reporter=json-summary npm run test:coverage:cases",
     "test:coverage:cases": "node tests/unit/coverage-script-contract.test.mjs && node tests/unit/attachment-status.test.mjs && node tests/unit/clearfolio-status-signal.test.mjs && node tests/unit/clearfolio-adapter-mock-hmac.test.mjs && node tests/unit/orchestrator.test.mjs && node tests/unit/orchestrator-coverage.test.mjs && node tests/unit/orchestrator-attribution.test.mjs && node tests/unit/msproject.test.mjs && node tests/unit/auth-password.test.mjs && node tests/unit/editor-unsaved.test.mjs && node tests/unit/static-coverage-evidence.test.mjs && npm run test:api",
-    "test:e2e": "playwright test",
-    "test:e2e:headed": "playwright test --headed",
-    "test:e2e:cloud": "playwright install chromium && playwright test tests/e2e/cloud.spec.js tests/e2e/toast-accessibility.spec.js",
+    "test:e2e": "playwright test --grep-invert @benchmark",
+    "test:e2e:headed": "playwright test --headed --grep-invert @benchmark",
+    "test:e2e:cloud": "playwright install chromium && playwright test tests/e2e/cloud.spec.js tests/e2e/toast-accessibility.spec.js tests/e2e/date-format-performance.spec.js",
     "test:fuzz": "playwright install chromium && playwright test tests/e2e/csv_formula_fuzz.spec.js",
     "fuzz": "node --test tests/fuzz/*.mjs"
   },