diff --git a/src/lib/onboard/machine/flow-phases/agent-policy-finalization.test.ts b/src/lib/onboard/machine/flow-phases/agent-policy-finalization.test.ts
index 5f848695f23..6032686b82a 100644
--- a/src/lib/onboard/machine/flow-phases/agent-policy-finalization.test.ts
+++ b/src/lib/onboard/machine/flow-phases/agent-policy-finalization.test.ts
@@ -5,7 +5,6 @@ import { describe, expect, it } from "vitest";
 
 import type { OnboardFlowContext } from "../flow-context";
 import { advanceTo, completeOnboardMachine } from "../result";
-import { OnboardRuntime, type OnboardRuntimeDeps } from "../runtime";
 import { runOnboardSequenceWithRunner } from "../sequence-runner";
 import {
   createAgentSetupPhase,
@@ -17,8 +16,6 @@ import {
 import {
   MACHINE_SNAPSHOT_VERSION,
   type Session,
-  type SessionUpdates,
-  cloneSession,
   createSession,
   createTestRuntime,
 } from "../../../../../test/helpers/onboard-machine-runtime-fixture";
diff --git a/src/lib/onboard/machine/flow-sequence.test.ts b/src/lib/onboard/machine/flow-sequence.test.ts
index 1fe51188963..e964cd28537 100644
--- a/src/lib/onboard/machine/flow-sequence.test.ts
+++ b/src/lib/onboard/machine/flow-sequence.test.ts
@@ -7,13 +7,10 @@ import type { OnboardFlowContext, OnboardFlowPhaseResult } from "./flow-context"
 import { onboardFlowPhaseResult } from "./flow-context";
 import { buildOnboardFlowPhaseSequence } from "./flow-sequence";
 import { advanceTo, branchTo, completeOnboardMachine } from "./result";
-import { OnboardRuntime, type OnboardRuntimeDeps } from "./runtime";
 import { runOnboardSequenceWithRunner } from "./sequence-runner";
 import {
   MACHINE_SNAPSHOT_VERSION,
   type Session,
-  type SessionUpdates,
-  cloneSession,
   createSession,
   createTestRuntime,
 } from "../../../../test/helpers/onboard-machine-runtime-fixture";
diff --git a/src/lib/onboard/machine/runner-sequence.test.ts b/src/lib/onboard/machine/runner-sequence.test.ts
index 8a13f838e36..08c556d1013 100644
--- a/src/lib/onboard/machine/runner-sequence.test.ts
+++ b/src/lib/onboard/machine/runner-sequence.test.ts
@@ -12,12 +12,8 @@ import {
   type OnboardStateHandlers,
   runOnboardMachine,
 } from "./runner";
-import { OnboardRuntime, type OnboardRuntimeDeps } from "./runtime";
 import {
   MACHINE_SNAPSHOT_VERSION,
-  type Session,
-  type SessionUpdates,
-  cloneSession,
   createSession,
   createTestRuntime as createRuntime,
 } from "../../../../test/helpers/onboard-machine-runtime-fixture";
diff --git a/src/lib/onboard/machine/runner.test.ts b/src/lib/onboard/machine/runner.test.ts
index 5d5bca43c8a..727dd3acf06 100644
--- a/src/lib/onboard/machine/runner.test.ts
+++ b/src/lib/onboard/machine/runner.test.ts
@@ -17,12 +17,8 @@ import {
   type OnboardStateHandlers,
   runOnboardMachine,
 } from "./runner";
-import { OnboardRuntime, type OnboardRuntimeDeps } from "./runtime";
 import {
   MACHINE_SNAPSHOT_VERSION,
-  type Session,
-  type SessionUpdates,
-  cloneSession,
   createSession,
   createTestRuntime as createRuntime,
 } from "../../../../test/helpers/onboard-machine-runtime-fixture";
diff --git a/src/lib/onboard/machine/runtime.test.ts b/src/lib/onboard/machine/runtime.test.ts
index d76820af90a..1d67a40bbb1 100644
--- a/src/lib/onboard/machine/runtime.test.ts
+++ b/src/lib/onboard/machine/runtime.test.ts
@@ -120,6 +120,19 @@ function sessionInState(state: Session["machine"]["state"]): Session {
   return session;
 }
 
+describe("onboard machine runtime fixture", () => {
+  it("keeps fallback clones isolated when normalization rejects a session (#8289)", () => {
+    const original = createSession();
+    original.version = 0;
+
+    const cloned = cloneSession(original);
+    cloned.steps.preflight.status = "complete";
+
+    expect(cloned).not.toBe(original);
+    expect(original.steps.preflight.status).toBe("pending");
+  });
+});
+
 describe("OnboardRuntime", () => {
   it("starts a session and emits started/resumed lifecycle events", async () => {
     const { runtime, events, getSession } = createHarness(null);
diff --git a/src/lib/onboard/machine/sequence-runner.test.ts b/src/lib/onboard/machine/sequence-runner.test.ts
index ed8c3026baf..5d75ce185a4 100644
--- a/src/lib/onboard/machine/sequence-runner.test.ts
+++ b/src/lib/onboard/machine/sequence-runner.test.ts
@@ -4,7 +4,6 @@
 import { describe, expect, it } from "vitest";
 
 import { advanceTo, branchTo, completeOnboardMachine, retryTo } from "./result";
-import { OnboardRuntime, type OnboardRuntimeDeps } from "./runtime";
 import {
   buildOnboardSequenceHandlers,
   DuplicateOnboardSequencePhaseError,
@@ -13,8 +12,6 @@ import {
 } from "./sequence-runner";
 import {
   type Session,
-  type SessionUpdates,
-  cloneSession,
   createSession,
   createTestRuntime,
 } from "../../../../test/helpers/onboard-machine-runtime-fixture";
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. */