diff --git a/docs/release-control/v6/internal/subsystems/deployment-installability.md b/docs/release-control/v6/internal/subsystems/deployment-installability.md
index c36bebc96..0066c6ccb 100644
--- a/docs/release-control/v6/internal/subsystems/deployment-installability.md
+++ b/docs/release-control/v6/internal/subsystems/deployment-installability.md
@@ -2366,6 +2366,17 @@ artifact-selection behaviour.
    `scripts/trigger-release.sh` and `scripts/trigger-stable-patch.sh` must send
    the exact remote candidate SHA they already verified; branch ancestry or a
    later branch tip is not equivalent release admission.
+18. Keep the frontend type-surface dependency and its compiler lib aligned.
+   `frontend-modern/package.json` and `frontend-modern/package-lock.json` must
+   pin a single `@types/node` line at or above the reviewed floor with its
+   `undici-types` companion resolved consistently, and
+   `frontend-modern/tsconfig.json` must declare the `ES2022` lib whenever the
+   source uses `Array.prototype.at()`/`String.prototype.at()`. `@types/node`
+   before 26 shipped an `.at()` compatibility polyfill that masked the missing
+   lib; a bump that removes it must keep
+   `frontend-modern/src/security/__tests__/dependencySecurity.test.ts` proving
+   the manifest range, the locked `@types/node`/`undici-types` versions and the
+   `ES2022` lib declaration stay in step.
 
 ## Current State
 
diff --git a/frontend-modern/package-lock.json b/frontend-modern/package-lock.json
index 1cd175933..7bc5c96d0 100644
--- a/frontend-modern/package-lock.json
+++ b/frontend-modern/package-lock.json
@@ -22,7 +22,7 @@
         "@solidjs/testing-library": "^0.8.5",
         "@tailwindcss/typography": "^0.5.19",
         "@testing-library/jest-dom": "^6.5.0",
-        "@types/node": "^20.10.0",
+        "@types/node": "^26.5.1",
         "@types/qrcode": "^1.5.6",
         "@typescript-eslint/eslint-plugin": "^8.24.0",
         "@typescript-eslint/parser": "^8.24.0",
@@ -1969,13 +1969,13 @@
       "license": "MIT"
     },
     "node_modules/@types/node": {
-      "version": "20.19.43",
-      "resolved": "https://registry.npmjs.org/@types/node/-/node-20.19.43.tgz",
-      "integrity": "sha512-6oYBAi5ikg4Pl+kGsoYtawUMBT2zZMCvPNF7pVLnHZfd1zf38DRiWn/gT01RYCdUqkv7Fhr+C9ot4/tb+2sVvA==",
+      "version": "26.5.1",
+      "resolved": "https://registry.npmjs.org/@types/node/-/node-26.5.1.tgz",
+      "integrity": "sha512-CzNm2FezW4VR/LjG6yUdiEgLE/rAQ9Slj5gCu/C2VrdcW7I0ahNZ8DRbHT7zOZ6r3ONgd/bsQIeSaoDGrd1C6g==",
       "dev": true,
       "license": "MIT",
       "dependencies": {
-        "undici-types": "~6.21.0"
+        "undici-types": "~8.9.0"
       }
     },
     "node_modules/@types/qrcode": {
@@ -6473,9 +6473,9 @@
       }
     },
     "node_modules/undici-types": {
-      "version": "6.21.0",
-      "resolved": "https://registry.npmjs.org/undici-types/-/undici-types-6.21.0.tgz",
-      "integrity": "sha512-iwDZqg0QAGrg9Rav5H4n0M64c3mkR59cJ6wQp+7C4nI0gsmExaedaYLNO44eT4AtBBwjbTiGPMlt2Md0T9H9JQ==",
+      "version": "8.9.0",
+      "resolved": "https://registry.npmjs.org/undici-types/-/undici-types-8.9.0.tgz",
+      "integrity": "sha512-KTDyRTYX8sWmKXAikPHHSyc63CRPETMctyjKFupcC6OBLXT3xsN0e9aF7m+mIXutFWpUXuedtowG7iLOzp0kQg==",
       "dev": true,
       "license": "MIT"
     },
diff --git a/frontend-modern/package.json b/frontend-modern/package.json
index 6289dc6c4..b52ba77fd 100644
--- a/frontend-modern/package.json
+++ b/frontend-modern/package.json
@@ -73,7 +73,7 @@
     "@solidjs/testing-library": "^0.8.5",
     "@tailwindcss/typography": "^0.5.19",
     "@testing-library/jest-dom": "^6.5.0",
-    "@types/node": "^20.10.0",
+    "@types/node": "^26.5.1",
     "@types/qrcode": "^1.5.6",
     "@typescript-eslint/eslint-plugin": "^8.24.0",
     "@typescript-eslint/parser": "^8.24.0",
diff --git a/frontend-modern/src/security/__tests__/dependencySecurity.test.ts b/frontend-modern/src/security/__tests__/dependencySecurity.test.ts
index 774241c3b..aafd006d8 100644
--- a/frontend-modern/src/security/__tests__/dependencySecurity.test.ts
+++ b/frontend-modern/src/security/__tests__/dependencySecurity.test.ts
@@ -20,6 +20,13 @@ const lock = JSON.parse(
   readFileSync(new URL('../../../package-lock.json', import.meta.url), 'utf8'),
 ) as PackageLock;
 
+const tsconfig = readFileSync(new URL('../../../tsconfig.json', import.meta.url), 'utf8');
+const libMatch = /"lib"\s*:\s*\[([^\]]*)\]/.exec(tsconfig);
+const declaredLib = (libMatch?.[1] ?? '')
+  .split(',')
+  .map((entry) => entry.trim().replace(/^"|"$/g, ''))
+  .filter(Boolean);
+
 const parseVersion = (version: string): [number, number, number] => {
   const [major = 0, minor = 0, patch = 0] = version
     .split('-', 1)[0]
@@ -139,4 +146,29 @@ describe('frontend dependency security floors', () => {
       expect(atLeast(version, [4, 28, 7]), `browserslist ${version} is vulnerable`).toBe(true);
     }
   });
+
+  it('keeps @types/node and its undici-types companion aligned with the declared ES2022 lib', () => {
+    // @types/node 20 shipped an .at() compatibility polyfill that masked the
+    // missing ES2022 lib; 26 drops it, so tsconfig must declare ES2022 itself
+    // (Dependabot #2099). Keep the manifest range, the lock and the lib in step.
+    const range = manifest.devDependencies['@types/node'];
+    expect(/^\^26\.\d+\.\d+$/.test(range), `unexpected @types/node range ${range}`).toBe(true);
+    expect(atLeast(range.slice(1), [26, 5, 1])).toBe(true);
+    const nodeTypes = lockedVersions('@types/node');
+    expect(nodeTypes).toHaveLength(1);
+    expect(nodeTypes[0]).not.toContain('-');
+    expect(
+      atLeast(nodeTypes[0], [26, 5, 1]),
+      `@types/node ${nodeTypes[0]} is below the reviewed floor`,
+    ).toBe(true);
+    const undici = lockedVersions('undici-types');
+    expect(undici).not.toHaveLength(0);
+    for (const version of undici) {
+      expect(
+        atLeast(version, [8, 9, 0]),
+        `undici-types ${version} must satisfy @types/node 26`,
+      ).toBe(true);
+    }
+    expect(declaredLib).toContain('ES2022');
+  });
 });