fix(#411): narrow verifySession allowlist — prevent false-positive infra error classification

Replace broad "expired" and "unauthorized" substring matches with specific
patterns to prevent infrastructure errors from being misclassified as auth
errors:

- "expired" -> "token expired", "session expired", or exact match "expired"
- "unauthorized" -> exact match "unauthorized" only

This prevents TLS errors like "certificate has expired" and DB auth errors
like "Unauthorized: Access denied for user" from being silently swallowed
as 401 responses.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/api/src/auth/auth.service.spec.ts

@@ -485,6 +485,60 @@ describe("AuthService", () => {
       expect(result).toBeNull();
     });
 
+    it("should return null for 'session expired' auth error", async () => {
+      const auth = service.getAuth();
+      const mockGetSession = vi.fn().mockRejectedValue(new Error("Session expired"));
+      auth.api = { getSession: mockGetSession } as any;
+
+      const result = await service.verifySession("expired-session");
+
+      expect(result).toBeNull();
+    });
+
+    it("should return null for bare 'unauthorized' (exact match)", async () => {
+      const auth = service.getAuth();
+      const mockGetSession = vi.fn().mockRejectedValue(new Error("unauthorized"));
+      auth.api = { getSession: mockGetSession } as any;
+
+      const result = await service.verifySession("unauth-token");
+
+      expect(result).toBeNull();
+    });
+
+    it("should return null for bare 'expired' (exact match)", async () => {
+      const auth = service.getAuth();
+      const mockGetSession = vi.fn().mockRejectedValue(new Error("expired"));
+      auth.api = { getSession: mockGetSession } as any;
+
+      const result = await service.verifySession("expired-token");
+
+      expect(result).toBeNull();
+    });
+
+    it("should re-throw 'certificate has expired' as infrastructure error (not auth)", async () => {
+      const auth = service.getAuth();
+      const mockGetSession = vi
+        .fn()
+        .mockRejectedValue(new Error("certificate has expired"));
+      auth.api = { getSession: mockGetSession } as any;
+
+      await expect(service.verifySession("any-token")).rejects.toThrow(
+        "certificate has expired"
+      );
+    });
+
+    it("should re-throw 'Unauthorized: Access denied for user' as infrastructure error (not auth)", async () => {
+      const auth = service.getAuth();
+      const mockGetSession = vi
+        .fn()
+        .mockRejectedValue(new Error("Unauthorized: Access denied for user"));
+      auth.api = { getSession: mockGetSession } as any;
+
+      await expect(service.verifySession("any-token")).rejects.toThrow(
+        "Unauthorized: Access denied for user"
+      );
+    });
+
     it("should return null when a non-Error value is thrown", async () => {
       const auth = service.getAuth();
       const mockGetSession = vi.fn().mockRejectedValue("string-error");