diff --git a/tsconfig.typecheck.json b/tsconfig.typecheck.json
new file mode 100644
index 000000000..f28873ee4
--- /dev/null
+++ b/tsconfig.typecheck.json
@@ -0,0 +1,10 @@
+{
+  "extends": "./tsconfig.json",
+  "compilerOptions": {
+    "composite": false,
+    "incremental": false,
+    "noEmit": true
+  },
+  "include": ["packages/ai/src/**/*"],
+  "exclude": ["**/dist", "**/node_modules"]
+}
diff --git a/vitest.config.ts b/vitest.config.ts
index 008db3b2a..3b9a33e4d 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -8,6 +8,13 @@ export default defineConfig({
   envDir: __dirname,
   test: {
     setupFiles: ["./vitest.setup.ts"],
+    // The nightly type-drift guard runs `.test-d.ts` files through vitest's
+    // `--typecheck` engine. Scope the tsc program to the package under test so
+    // unrelated source (example UIs needing `jsx`, providers relying on their
+    // own ambient `types`/`lib`) is not swept in and reported as drift.
+    typecheck: {
+      tsconfig: "./tsconfig.typecheck.json",
+    },
     testTimeout: 15000, // 15 second global timeout (WASM Postgres / PGlite init can be slow)
     // Vitest uses hookTimeout for beforeEach/afterAll separately from testTimeout; keep both aligned
     hookTimeout: 15000,