diff --git a/packages/auth/src/di/bind-production.types.test.ts b/packages/auth/src/di/bind-production.types.test.ts
new file mode 100644
index 0000000..7782a3a
--- /dev/null
+++ b/packages/auth/src/di/bind-production.types.test.ts
@@ -0,0 +1,28 @@
+import { describe, it } from "vitest";
+import type { ProductionUseCase } from "@repo/core-shared/conformance";
+import type { AuthManifest } from "../feature.manifest";
+import type {
+  SignInInput,
+  SignInOutput,
+} from "../application/use-cases/sign-in.use-case";
+import { signInUseCase } from "../application/use-cases/sign-in.use-case";
+
+describe("auth.signIn binding slot (type-level)", () => {
+  it("rejects an unwrapped factory", () => {
+    type Slot = ProductionUseCase<
+      SignInInput,
+      SignInOutput,
+      AuthManifest["useCases"]["signIn"]
+    >;
+
+    // Build the unwrapped factory exactly as it would be at the use-case file.
+    // It returns a function with no brand attached — must not be assignable.
+    const fakeRepo = {} as never;
+    const fakeAuth = {} as never;
+    const unwrapped = signInUseCase(fakeRepo, fakeAuth);
+
+    // @ts-expect-error — unwrapped factory has no __instrumented / __captured brand
+    const _bad: Slot = unwrapped;
+    void _bad;
+  });
+});