diff --git a/test/helpers/onboard-machine-runtime-fixture.test.ts b/test/helpers/onboard-machine-runtime-fixture.test.ts
new file mode 100644
index 00000000000..0954f96ad91
--- /dev/null
+++ b/test/helpers/onboard-machine-runtime-fixture.test.ts
@@ -0,0 +1,23 @@
+// SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+import { describe, expect, it } from "vitest";
+import { cloneSession, createSession } from "./onboard-machine-runtime-fixture";
+
+describe("cloneSession", () => {
+  it("isolates invalid session state when normalization rejects the copy", () => {
+    const session = createSession();
+    session.version = 0;
+
+    const copy = cloneSession(session);
+
+    expect(copy).not.toBe(session);
+    expect(copy.steps).not.toBe(session.steps);
+
+    copy.status = "failed";
+    copy.steps.preflight.status = "failed";
+
+    expect(session.status).toBe("in_progress");
+    expect(session.steps.preflight.status).toBe("pending");
+  });
+});
diff --git a/test/helpers/onboard-machine-runtime-fixture.ts b/test/helpers/onboard-machine-runtime-fixture.ts
index 58b88d01a95..78287c67be8 100644
--- a/test/helpers/onboard-machine-runtime-fixture.ts
+++ b/test/helpers/onboard-machine-runtime-fixture.ts
@@ -27,7 +27,8 @@ export type { Session, SessionUpdates } from "../../src/lib/state/onboard-sessio
 
 /** A deep session copy that survives independent mutation. */
 export function cloneSession(session: Session): Session {
-  return normalizeSession(JSON.parse(JSON.stringify(session))) ?? session;
+  const copy = JSON.parse(JSON.stringify(session)) as Session;
+  return normalizeSession(copy) ?? copy;
 }
 
 /** Behavior options for createTestRuntime. */