diff --git a/CHANGELOG.md b/CHANGELOG.md
index e3d1f9b..711b4ab 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -42,6 +42,8 @@ Follows [Keep a Changelog](https://keepachangelog.com/en/1.0.0/) · versioned wi
   secrets, audio, and image payloads are excluded from persistence.
 - **Bounded Durable Job Retention.** Completed background-job metadata is pruned oldest-first at a fixed limit so
   restart-safe status tracking cannot become an unbounded database growth path.
+- **Frontend Quality Gate.** Added `npm run check:frontend` to validate every manifest module for syntax errors,
+  duplicate manifest entries, and top-level declaration collisions before bundling.
 - **STT Cancellation Safety.** Queued transcription cancels before consuming the single STT slot, and timed-out
   requests keep the device slot held until the underlying worker actually exits.
 - **Credential Boundary Review.** Provider credentials are now documented as server-only; only the explicitly
diff --git a/TODO.md b/TODO.md
index 7e1a68f..e2c7b08 100644
--- a/TODO.md
+++ b/TODO.md
@@ -104,7 +104,8 @@ the first block before investing in architecture or polish.
 - [ ] Replace broad globals with namespaces such as `window.TTVC.audiobook`.
 - [x] Generate the feature-module list for `loader.js` and `scripts/minify.mjs` from one shared manifest;
   larger responsibility splits remain.
-- [ ] Add linting and duplicate-function checks.
+- [x] Add a dependency-free frontend syntax and top-level declaration collision gate (`npm run check:frontend`);
+  a full style/lint policy remains a follow-up.
 - [ ] Extract Rehearser voice matching and voice design.
 - [ ] Extract Audiobook parsing and casting.
 - [ ] Split `style.css` by feature.
diff --git a/VERSION b/VERSION
index a6c2798..49e0a31 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-1.23.0
+1.23.1
diff --git a/package.json b/package.json
index 6f022db..c8d3c1b 100644
--- a/package.json
+++ b/package.json
@@ -8,7 +8,8 @@
     "test:headed": "playwright test --headed",
     "test:ui": "playwright test --ui",
     "install:browsers": "playwright install chromium",
-    "minify": "node scripts/minify.mjs"
+    "minify": "node scripts/minify.mjs",
+    "check:frontend": "node scripts/check-frontend.mjs"
   },
   "devDependencies": {
     "@playwright/test": "^1.48.0",
diff --git a/scripts/check-frontend.mjs b/scripts/check-frontend.mjs
new file mode 100644
index 0000000..8a39997
--- /dev/null
+++ b/scripts/check-frontend.mjs
@@ -0,0 +1,36 @@
+// Fast, dependency-free frontend gate. The application deliberately shares one
+// global scope, so duplicate top-level declarations are a runtime collision.
+// Nested callbacks are ignored; vendor/PDF bundles are outside the manifest.
+import { execFileSync } from 'node:child_process';
+import { readFileSync } from 'node:fs';
+import { join } from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const root = join(fileURLToPath(new URL('.', import.meta.url)), '..');
+const modules = JSON.parse(readFileSync(join(root, 'static', 'module-manifest.json'), 'utf8'));
+const seenModules = new Set();
+const declarations = new Map();
+const declarationPattern = /^(?:async\s+)?(?:function|class|const|let|var)\s+([A-Za-z_$][\w$]*)/gm;
+
+for (const name of modules) {
+  if (seenModules.has(name)) throw new Error(`duplicate module in manifest: ${name}`);
+  seenModules.add(name);
+  const file = join(root, 'static', 'js', name + '.js');
+  try {
+    execFileSync(process.execPath, ['--check', file], { stdio: 'pipe' });
+  } catch (error) {
+    throw new Error(`JavaScript syntax check failed for ${file}: ${error.stderr?.toString().trim() || error.message}`);
+  }
+  const source = readFileSync(file, 'utf8');
+  for (const match of source.matchAll(declarationPattern)) {
+    const files = declarations.get(match[1]) || [];
+    files.push(file);
+    declarations.set(match[1], files);
+  }
+}
+
+const collisions = [...declarations.entries()].filter(([, files]) => files.length > 1);
+if (collisions.length) {
+  throw new Error('duplicate top-level declarations:\n' + collisions.map(([name, files]) => `  ${name}: ${files.join(', ')}`).join('\n'));
+}
+console.log(`Frontend gate passed: ${modules.length} modules, no syntax errors or top-level declaration collisions.`);