FLEET: session.task_complete does not fire after fleet execution #2262

Summary

session.task_complete — which fires reliably after a normal sendAndWait() turn — never fires after fleet execution completes. There is no clean fleet-done signal.

Steps to Reproduce

const session = await client.createSession({
    onPermissionRequest: async () => ({ approved: true }),
});

let taskCompleteCount = 0;
session.on('session.task_complete', () => taskCompleteCount++);

session.on('session.idle', () => {
    console.log(`task_complete fired ${taskCompleteCount} times`);
    // → "task_complete fired 0 times"
});

await session.rpc.fleet.start({ prompt: 'Research X and Y in parallel' });

Observed Behaviour

session.task_complete fired 0 times across all fleet runs. Spike data (2026-03-17) for a 4-subagent run with 757 total events:

{
  "session.background_tasks_changed": 172,
  "subagent.started": 4,
  "subagent.completed": 2,
  "session.idle": 1,
  "session.task_complete": 0
}

session.task_complete fires normally for regular sendAndWait() turns — fleet is the only case where it doesn't.

Expected Behaviour

session.task_complete should fire when fleet finishes all sub-agents, consistent with regular turn behaviour. Alternatively, a dedicated fleet.complete event should be introduced.

Workaround

Wait on session.idle, but see related issue FLEET-3 — session.idle fires before all sub-agents finish, making this imprecise.

Environment

• SDK: @github/copilot-sdk v0.1.32
• CLI: latest
• Node: v24.13.1