fix(tmux-subagent): avoid transcript fetches during idle stability checks

src/features/tmux-subagent/polling-manager.test.ts

@@ -55,4 +55,55 @@ describe("TmuxPollingManager overlap", () => {
     expect(maxActiveCalls).toBe(1)
     expect(statusCallCount).toBe(1)
   })
+
+  test("closes stable idle sessions without fetching full messages when activity was already observed from events", async () => {
+    //#given
+    const sessions = new Map<string, TrackedSession>()
+    sessions.set("ses-1", {
+      sessionId: "ses-1",
+      paneId: "%1",
+      description: "test",
+      createdAt: new Date(Date.now() - 15_000),
+      lastSeenAt: new Date(),
+      closePending: false,
+      closeRetryCount: 0,
+      activityVersion: 0,
+    })
+
+    let messagesCallCount = 0
+    const closedSessionIds: string[] = []
+    const client = {
+      session: {
+        status: async () => ({ data: { "ses-1": { type: "idle" } } }),
+        messages: async () => {
+          messagesCallCount += 1
+          return { data: [] }
+        },
+      },
+    }
+
+    const manager = new TmuxPollingManager(
+      client as unknown as import("../../tools/delegate-task/types").OpencodeClient,
+      sessions,
+      async (sessionId) => {
+        closedSessionIds.push(sessionId)
+      },
+    )
+
+    manager.handleEvent({
+      type: "message.part.delta",
+      properties: { sessionID: "ses-1", field: "text", delta: "done" },
+    })
+
+    //#when
+    const pollSessions = (manager as unknown as { pollSessions: () => Promise<void> }).pollSessions
+    await pollSessions.call(manager)
+    await pollSessions.call(manager)
+    await pollSessions.call(manager)
+    await pollSessions.call(manager)
+
+    //#then
+    expect(messagesCallCount).toBe(0)
+    expect(closedSessionIds).toEqual(["ses-1"])
+  })
 })