diff --git a/src/main/native-chat/agent-session-wire/structured-agent-session-lease-renewer.test.ts b/src/main/native-chat/agent-session-wire/structured-agent-session-lease-renewer.test.ts
index e5b97dea189..f91ea0a1922 100644
--- a/src/main/native-chat/agent-session-wire/structured-agent-session-lease-renewer.test.ts
+++ b/src/main/native-chat/agent-session-wire/structured-agent-session-lease-renewer.test.ts
@@ -6,6 +6,7 @@ import {
   agentSessionLeaseFixture,
   agentSessionRecordFixture
 } from '../../../shared/agent-session-record.test-fixture'
+import { stopStoredAgentSessionOwnerForHandoff } from '../../runtime/agent-session-handoff-record-transitions'
 import { AgentSessionRecordStore } from '../../runtime/agent-session-record-store'
 import { StructuredAgentSessionLeaseRenewer } from './structured-agent-session-lease-renewer'
 
@@ -264,6 +265,58 @@ describe('structured agent-session lease renewal', () => {
     expect(store.getRecord('session-renewal')?.lease.lastRenewedAt).toBe(NOW)
   })
 
+  it('does not preempt a native owner handoff after the child stops', async () => {
+    const store = await liveStore()
+    const initialFence = store.getRecord('session-renewal')!.lease.runtimeFence
+    const probeStarted = Promise.withResolvers<void>()
+    const deadProbe = Promise.withResolvers<{ outcome: 'pid-absent' }>()
+    const onError = vi.fn()
+    const renewer = new StructuredAgentSessionLeaseRenewer({
+      store,
+      probe: async () => {
+        probeStarted.resolve()
+        return deadProbe.promise
+      },
+      now: () => NOW + 10_000,
+      onError
+    })
+    const renewal = renewer.renewNow()
+    await probeStarted.promise
+    await store.transitionHandoff('session-renewal', (record) => ({
+      ...record,
+      lease: {
+        ...record.lease,
+        handoffStage: 'preparing',
+        handoffOperationId: 'handoff-1'
+      }
+    }))
+    deadProbe.resolve({ outcome: 'pid-absent' })
+    await renewal
+
+    expect(store.getRecord('session-renewal')?.lease).toMatchObject({
+      runtimeFence: initialFence,
+      handoffStage: 'preparing',
+      handoffOperationId: 'handoff-1',
+      claimStatus: 'live'
+    })
+    expect(onError).toHaveBeenCalledWith({
+      sessionId: 'session-renewal',
+      error: expect.objectContaining({ message: 'agent_session_checkpoint_stale' })
+    })
+    const stopped = await stopStoredAgentSessionOwnerForHandoff(store, {
+      sessionId: 'session-renewal',
+      expectedFence: initialFence,
+      operationId: 'handoff-1',
+      now: NOW + 10_001
+    })
+    expect(stopped.lease).toMatchObject({
+      runtimeFence: initialFence + 1,
+      handoffStage: 'old-owner-stopped',
+      handoffOperationId: 'handoff-1',
+      claimStatus: 'released'
+    })
+  })
+
   it('routes a proven dead TUI owner into handoff recovery', async () => {
     const store = await liveStore()
     await store.transitionHandoff('session-renewal', (record) => ({
diff --git a/src/main/native-chat/agent-session-wire/structured-agent-session-lease-renewer.ts b/src/main/native-chat/agent-session-wire/structured-agent-session-lease-renewer.ts
index e4ea2bd30f5..949f1c305ac 100644
--- a/src/main/native-chat/agent-session-wire/structured-agent-session-lease-renewer.ts
+++ b/src/main/native-chat/agent-session-wire/structured-agent-session-lease-renewer.ts
@@ -76,13 +76,18 @@ export class StructuredAgentSessionLeaseRenewer {
         if (!probe) {
           continue
         }
-        // Positive death evidence settles it; the deadline only guards a live owner that has not
-        // renewed yet. Matches the dead-TUI-owner branch below, which never waits for expiry.
-        if (record.lease.runtimeKind === 'native' && isProvenDeadProbe(probe)) {
+        // Positive death evidence settles an idle owner without waiting for expiry. An active
+        // handoff owns its stop transition and fence; the renewer must not preempt it.
+        if (
+          record.lease.runtimeKind === 'native' &&
+          record.lease.handoffStage === null &&
+          isProvenDeadProbe(probe)
+        ) {
           try {
             await this.input.store.evictProvenDeadOwner({
               sessionId: record.sessionId,
               expectedFence: record.lease.runtimeFence,
+              expectedHandoffStage: null,
               probe,
               now
             })
diff --git a/src/main/runtime/agent-session-lease-transitions.ts b/src/main/runtime/agent-session-lease-transitions.ts
index 28617817647..d4f41e5e3a1 100644
--- a/src/main/runtime/agent-session-lease-transitions.ts
+++ b/src/main/runtime/agent-session-lease-transitions.ts
@@ -203,15 +203,25 @@ export function renewAgentSessionLease(args: {
 }
 
 /** Proven eviction — the only other thing besides acquisition that may move the fence. */
-export function evictAgentSessionOwner(args: {
+export type EvictAgentSessionOwnerInput = {
   record: AgentSessionRecord
   expectedFence: number
+  /** Compare-and-swap guard: a stage that drifted since the scan must not be clobbered. */
+  expectedHandoffStage?: AgentSessionRecord['lease']['handoffStage']
   probe: AgentSessionOwnerProbe
   now: number
   journalSettlement: 'required' | 'not-required'
-}): AgentSessionRecord {
+}
+
+export function evictAgentSessionOwner(args: EvictAgentSessionOwnerInput): AgentSessionRecord {
   const { record } = args
   assertFence(record.lease, args.expectedFence)
+  if (
+    args.expectedHandoffStage !== undefined &&
+    record.lease.handoffStage !== args.expectedHandoffStage
+  ) {
+    throw new Error('agent_session_checkpoint_stale')
+  }
   if (record.lease.settlementRetryRequired) {
     throw new Error('agent_session_ownership_unknown')
   }
diff --git a/src/main/runtime/agent-session-record-store.ts b/src/main/runtime/agent-session-record-store.ts
index 4325410ed81..07f573fc576 100644
--- a/src/main/runtime/agent-session-record-store.ts
+++ b/src/main/runtime/agent-session-record-store.ts
@@ -13,7 +13,6 @@ import {
   admitAgentSessionOperationRow,
   type AgentSessionOperationAdmission
 } from './agent-session-operation-admission'
-import type { AgentSessionOwnerProbe } from '../../shared/agent-session-lease-adjudication'
 import { classifyObservedAgentSessionSpawnToken } from '../../shared/agent-session-lease-adjudication'
 import type { AgentSessionProviderHandleLink } from '../../shared/agent-session-provider-handle'
 import {
@@ -28,7 +27,8 @@ import {
   evictAgentSessionOwner,
   proveAgentSessionOwner,
   setAgentSessionJournalCheckpoint,
-  type AgentSessionProcessIdentityCommit
+  type AgentSessionProcessIdentityCommit,
+  type EvictAgentSessionOwnerInput
 } from './agent-session-lease-transitions'
 import {
   settleFailedAgentSessionAcquisition,
@@ -248,12 +248,9 @@ export class AgentSessionRecordStore {
     )
   }
 
-  async evictProvenDeadOwner(args: {
-    sessionId: string
-    expectedFence: number
-    probe: AgentSessionOwnerProbe
-    now: number
-  }): Promise<AgentSessionRecord> {
+  async evictProvenDeadOwner(
+    args: Omit<EvictAgentSessionOwnerInput, 'record' | 'journalSettlement'> & { sessionId: string }
+  ): Promise<AgentSessionRecord> {
     return this.mutate(args.sessionId, (record) =>
       evictAgentSessionOwner({ ...args, record, journalSettlement: 'required' })
     )