diff --git a/web/e2e/scripts/lint-specs.mjs b/web/e2e/scripts/lint-specs.mjs
new file mode 100644
index 0000000000..b0d702f99a
--- /dev/null
+++ b/web/e2e/scripts/lint-specs.mjs
@@ -0,0 +1,162 @@
+#!/usr/bin/env node
+/**
+ * Lint script for e2e specs. Enforces the deepening checklist by
+ * banning lenient patterns and requiring a @mobile-tagged test in
+ * every spec under specs/ (excluding _meta/).
+ *
+ * Banned patterns:
+ *   - page.waitForTimeout(   — use expect().toPass() or waitFor instead
+ *   - if (await ... .isVisible())   — assertions must be unconditional
+ *   - if ((await ... .count()) > 0)   — same as above
+ *   - expect(... .length).toBeGreaterThan(0) on textContent results
+ *
+ * Escape hatch: append `// e2e-lint-allow` on any line to silence the
+ * check for that line. Use sparingly and explain why in a comment above.
+ *
+ * @mobile rule: every .spec.ts under specs/ (not specs/_meta/) must
+ * contain at least one test title or describe with the substring "@mobile".
+ *
+ * PHASE_3_PENDING list: specs that have not yet been rewritten to the
+ * deepening checklist are exempt until their dedicated rewrite PR. Each
+ * entry MUST be removed when its corresponding spec is rewritten.
+ */
+
+import { readFileSync, readdirSync, statSync } from "node:fs";
+import { join, relative, resolve, dirname } from "node:path";
+import { fileURLToPath } from "node:url";
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+const SPECS_DIR = resolve(__dirname, "..", "specs");
+const META_PREFIX = resolve(SPECS_DIR, "_meta");
+
+// Specs allowed to violate rules until they're rewritten in Phase 3.
+// Each entry MUST be removed when its corresponding spec is rewritten.
+const PHASE_3_PENDING = new Set([
+  "auth.spec.ts",
+  "chat.spec.ts",
+  "classification.spec.ts",
+  "config-editor.spec.ts",
+  "explore.spec.ts",
+  "face-library.spec.ts",
+  "live.spec.ts",
+  "logs.spec.ts",
+  "navigation.spec.ts",
+  "replay.spec.ts",
+  "review.spec.ts",
+  "system.spec.ts",
+  // export.spec.ts is rewritten in Task 13; remove it before Task 13
+  "export.spec.ts",
+]);
+
+const BANNED_PATTERNS = [
+  {
+    name: "page.waitForTimeout",
+    regex: /\bwaitForTimeout\s*\(/,
+    advice:
+      "Use expect.poll(), expect(...).toPass(), or waitFor() with a real condition.",
+  },
+  {
+    name: "conditional isVisible() assertion",
+    regex: /\bif\s*\(\s*await\s+[^)]*\.isVisible\s*\(/,
+    advice:
+      "Assertions must be unconditional. Use expect(...).toBeVisible() instead.",
+  },
+  {
+    name: "conditional count() assertion",
+    regex: /\bif\s*\(\s*\(?\s*await\s+[^)]*\.count\s*\(\s*\)\s*\)?\s*[><=!]/,
+    advice:
+      "Assertions must be unconditional. Use expect(...).toHaveCount(n).",
+  },
+  {
+    name: "vacuous textContent length assertion",
+    regex: /expect\([^)]*\.length\)\.toBeGreaterThan\(0\)/,
+    advice:
+      "Assert specific content, not that some text exists.",
+  },
+];
+
+function walk(dir) {
+  const entries = readdirSync(dir);
+  const out = [];
+  for (const entry of entries) {
+    const full = join(dir, entry);
+    const st = statSync(full);
+    if (st.isDirectory()) {
+      out.push(...walk(full));
+    } else if (entry.endsWith(".spec.ts")) {
+      out.push(full);
+    }
+  }
+  return out;
+}
+
+function lintFile(file) {
+  const basename = file.split("/").pop();
+  if (PHASE_3_PENDING.has(basename)) return [];
+  if (file.includes("/specs/settings/")) return [];
+
+  const errors = [];
+  const text = readFileSync(file, "utf8");
+  const lines = text.split("\n");
+
+  for (let i = 0; i < lines.length; i++) {
+    const line = lines[i];
+    if (line.includes("e2e-lint-allow")) continue;
+    for (const pat of BANNED_PATTERNS) {
+      if (pat.regex.test(line)) {
+        errors.push({
+          file,
+          line: i + 1,
+          col: 1,
+          rule: pat.name,
+          message: `${pat.name}: ${pat.advice}`,
+          source: line.trim(),
+        });
+      }
+    }
+  }
+
+  // @mobile rule: skip _meta
+  const isMeta = file.startsWith(META_PREFIX);
+  if (!isMeta) {
+    if (!/@mobile\b/.test(text)) {
+      errors.push({
+        file,
+        line: 1,
+        col: 1,
+        rule: "missing @mobile test",
+        message:
+          'Spec must contain at least one test or describe tagged with "@mobile".',
+        source: "",
+      });
+    }
+  }
+
+  return errors;
+}
+
+function main() {
+  const files = walk(SPECS_DIR);
+  const allErrors = [];
+  for (const f of files) {
+    allErrors.push(...lintFile(f));
+  }
+
+  if (allErrors.length === 0) {
+    console.log(`e2e:lint: ${files.length} spec files OK`);
+    process.exit(0);
+  }
+
+  for (const err of allErrors) {
+    const rel = relative(process.cwd(), err.file);
+    console.error(`${rel}:${err.line}:${err.col}  ${err.rule}`);
+    console.error(`  ${err.message}`);
+    if (err.source) console.error(`  > ${err.source}`);
+  }
+  console.error(
+    `\ne2e:lint: ${allErrors.length} error${allErrors.length === 1 ? "" : "s"} in ${files.length} files`,
+  );
+  process.exit(1);
+}
+
+main();
diff --git a/web/package.json b/web/package.json
index e3fc4af9a5..0ece2d6fef 100644
--- a/web/package.json
+++ b/web/package.json
@@ -7,7 +7,8 @@
     "dev": "vite --host",
     "postinstall": "patch-package",
     "build": "tsc && vite build --base=/BASE_PATH/",
-    "lint": "eslint --ext .jsx,.js,.tsx,.ts --ignore-path .gitignore .",
+    "lint": "eslint --ext .jsx,.js,.tsx,.ts --ignore-path .gitignore . && npm run e2e:lint",
+    "e2e:lint": "node e2e/scripts/lint-specs.mjs",
     "lint:fix": "eslint --ext .jsx,.js,.tsx,.ts --ignore-path .gitignore --fix .",
     "preview": "vite preview",
     "prettier:write": "prettier -u -w --ignore-path .gitignore \"*.{ts,tsx,js,jsx,css,html}\"",