diff --git a/src/main/daemon/daemon-server.test.ts b/src/main/daemon/daemon-server.test.ts
index 70536e64986..33e15964677 100644
--- a/src/main/daemon/daemon-server.test.ts
+++ b/src/main/daemon/daemon-server.test.ts
@@ -585,7 +585,10 @@ describe('DaemonServer', () => {
   })
 
   describe('idle self-exit', () => {
-    async function startServerWithIdleExit(graceMs: number): Promise<{
+    async function startServerWithIdleExit(
+      graceMs: number,
+      opts: { beforeStart?: (srv: DaemonServer) => Promise<void> } = {}
+    ): Promise<{
       idleExited: Promise<void>
       onIdleExit: ReturnType<typeof vi.fn>
       lastSubprocess: () => ReturnType<typeof createMockSubprocess> | null
@@ -606,6 +609,7 @@ describe('DaemonServer', () => {
         onIdleExit,
         idleExitGraceMs: graceMs
       })
+      await opts.beforeStart?.(server)
       await server.start()
       return { idleExited, onIdleExit, lastSubprocess: () => subprocess }
     }
@@ -684,15 +688,20 @@ describe('DaemonServer', () => {
     })
 
     it('never fires while a session is alive and exits after the last session ends', async () => {
-      const { idleExited, onIdleExit, lastSubprocess } = await startServerWithIdleExit(75)
-      const daemon = server as unknown as DaemonServerPrivate
-
-      // Create a session with zero connected clients — the exact state the
-      // daemon exists for (holding sessions across app restarts).
-      await daemon.routeRequest('ghost-client', {
-        id: 'req-idle-1',
-        type: 'createOrAttach',
-        payload: { sessionId: 'idle-session', cols: 80, rows: 24 }
+      // Why seed the session before start(): start() is what arms the
+      // countdown, so with a session already present the timer never arms at
+      // all. The invariant is proven deterministically instead of racing a
+      // cancel against a short grace on a loaded machine.
+      const { idleExited, onIdleExit, lastSubprocess } = await startServerWithIdleExit(75, {
+        beforeStart: async (srv) => {
+          // A session with zero connected clients — the exact state the
+          // daemon exists for (holding sessions across app restarts).
+          await (srv as unknown as DaemonServerPrivate).routeRequest('ghost-client', {
+            id: 'req-idle-1',
+            type: 'createOrAttach',
+            payload: { sessionId: 'idle-session', cols: 80, rows: 24 }
+          })
+        }
       })
       expect(idleArmed()).toBe(false)
 
diff --git a/src/main/daemon/terminal-host.test.ts b/src/main/daemon/terminal-host.test.ts
index 0f575f34003..b0fe2797a1d 100644
--- a/src/main/daemon/terminal-host.test.ts
+++ b/src/main/daemon/terminal-host.test.ts
@@ -516,4 +516,45 @@ describe('TerminalHost', () => {
       expect(liveSub.dispose).toHaveBeenCalled()
     })
   })
+
+  describe('onSessionCountChange', () => {
+    // Why: the daemon's idle-exit countdown arms/cancels purely off this hook;
+    // a missed notification on any transition silently disables idle exit (or
+    // worse, lets it fire with a session alive). Pin every transition.
+    it('notifies on create, natural-exit reap, and dispose', async () => {
+      const onSessionCountChange = vi.fn()
+      host.dispose()
+      host = new TerminalHost({
+        spawnSubprocess: spawnFn as MockSpawnFn,
+        onSessionCountChange
+      })
+
+      await host.createOrAttach({
+        sessionId: 'session-1',
+        cols: 80,
+        rows: 24,
+        streamClient: { onData: vi.fn(), onExit: vi.fn() }
+      })
+      expect(host.sessionCount()).toBe(1)
+      expect(onSessionCountChange).toHaveBeenCalledTimes(1)
+
+      // Natural exit reaps synchronously — this is the transition that lets
+      // an otherwise-empty daemon start its idle countdown.
+      lastSubprocess._onExitCb?.(0)
+      expect(host.sessionCount()).toBe(0)
+      expect(onSessionCountChange).toHaveBeenCalledTimes(2)
+
+      await host.createOrAttach({
+        sessionId: 'session-2',
+        cols: 80,
+        rows: 24,
+        streamClient: { onData: vi.fn(), onExit: vi.fn() }
+      })
+      expect(onSessionCountChange).toHaveBeenCalledTimes(3)
+
+      host.dispose()
+      expect(host.sessionCount()).toBe(0)
+      expect(onSessionCountChange).toHaveBeenCalledTimes(4)
+    })
+  })
 })