From fa52db8c6d015783fcaccfd6ea0f3d9fe8f36113 Mon Sep 17 00:00:00 2001
From: Neil <neil@stably.ai>
Date: Thu, 10 Sep 2026 17:40:33 -0700
Subject: [PATCH] test(runtime): pin replay containment on the deadline path
 too

Cherry-picked from aa98edf35ab (nwparker/adv3-failure-fixes) with its
implementation hunk dropped: a second agent found the same throwing-replay
hole independently, and `15f34014153` already closed it on this branch with
an equivalent guard. Applying both would have been a double-apply, and the
two spellings of the log line would have shipped side by side.

The tests are worth keeping regardless. The first duplicates coverage
15f34014153 already has; the second does not -- it drives the throw from the
DEADLINE path rather than the store-write path, which is a separate call into
releaseWaiter and was unpinned.

Spies retargeted from console.error to console.warn, the channel the guard
that actually shipped writes to, so the suite silences what the code emits.
---
 ...rror-handle-gap-replay-containment.test.ts | 82 +++++++++++++++++++
 1 file changed, 82 insertions(+)
 create mode 100644 src/renderer/src/lib/host-mirror-handle-gap-replay-containment.test.ts

diff --git a/src/renderer/src/lib/host-mirror-handle-gap-replay-containment.test.ts b/src/renderer/src/lib/host-mirror-handle-gap-replay-containment.test.ts
new file mode 100644
index 00000000000..ee651411c6a
--- /dev/null
+++ b/src/renderer/src/lib/host-mirror-handle-gap-replay-containment.test.ts
@@ -0,0 +1,82 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+import { useAppStore } from '@/store'
+import { clearRuntimeEnvironmentConnectionGenerationsForTests } from '@/store/slices/runtime-status'
+import {
+  HOST_MIRROR_HANDLE_GAP_DEADLINE_MS,
+  countParkedHostMirrorHandleGapPanesForTests,
+  parkUntilHostMirrorHandleLands,
+  resetHostMirrorHandleGapWaitsForTests
+} from './host-mirror-handle-gap-wait'
+
+// What this pins: the parked replay is `resumeSleepingAgentSessionsForWorktree`, a large
+// synchronous sweep, and it is released from inside `useAppStore.subscribe`. Zustand notifies
+// listeners in a plain loop, so a replay that throws escapes the `setState` that triggered it:
+// the listeners registered after this module never see the write, and every sibling pane the
+// same mirror frame made due is left parked. The waiter's own state is torn down before `run`,
+// so containing the throw holds nothing back.
+
+const initialAppStoreState = useAppStore.getState()
+const ENV_ID = 'env-gap-containment'
+
+function seedTwoMirroredPanes(): void {
+  useAppStore.setState({
+    tabsByWorktree: {
+      wt: [
+        { id: 'tab-a', title: 'a', ptyId: null },
+        { id: 'tab-b', title: 'b', ptyId: null }
+      ] as never
+    },
+    ptyIdsByTabId: {}
+  })
+}
+
+describe('host-mirror handle-gap replay containment', () => {
+  beforeEach(() => {
+    vi.useFakeTimers()
+    useAppStore.setState(initialAppStoreState, true)
+  })
+
+  afterEach(() => {
+    resetHostMirrorHandleGapWaitsForTests()
+    clearRuntimeEnvironmentConnectionGenerationsForTests()
+    useAppStore.setState(initialAppStoreState, true)
+    vi.useRealTimers()
+    vi.restoreAllMocks()
+  })
+
+  it('a replay that throws neither aborts the store write nor strands its sibling panes', () => {
+    vi.spyOn(console, 'warn').mockImplementation(() => {})
+    seedTwoMirroredPanes()
+    const siblingReplay = vi.fn()
+    parkUntilHostMirrorHandleLands(ENV_ID, 'wt', 'tab-a', () => {
+      throw new Error('replay blew up')
+    })
+    parkUntilHostMirrorHandleLands(ENV_ID, 'wt', 'tab-b', siblingReplay)
+    expect(countParkedHostMirrorHandleGapPanesForTests()).toBe(2)
+
+    // A store subscriber registered after this module's, so it is notified after the drain.
+    const laterSubscriber = vi.fn()
+    const unsubscribe = useAppStore.subscribe(laterSubscriber)
+
+    // One mirror frame lands both handles, making both waiters due on a single store write.
+    expect(() =>
+      useAppStore.setState({ ptyIdsByTabId: { 'tab-a': ['pty-a'], 'tab-b': ['pty-b'] } })
+    ).not.toThrow()
+    unsubscribe()
+
+    expect(siblingReplay).toHaveBeenCalledTimes(1)
+    expect(laterSubscriber).toHaveBeenCalledTimes(1)
+    expect(countParkedHostMirrorHandleGapPanesForTests()).toBe(0)
+  })
+
+  it('a replay that throws on the deadline path does not escape the timer', () => {
+    vi.spyOn(console, 'warn').mockImplementation(() => {})
+    seedTwoMirroredPanes()
+    parkUntilHostMirrorHandleLands(ENV_ID, 'wt', 'tab-a', () => {
+      throw new Error('replay blew up')
+    })
+
+    expect(() => vi.advanceTimersByTime(HOST_MIRROR_HANDLE_GAP_DEADLINE_MS)).not.toThrow()
+    expect(countParkedHostMirrorHandleGapPanesForTests()).toBe(0)
+  })
+})