Fix Pi approval continuation follow-up display

[xz-dev]

Summary

Follow-up to #805.

• Keep the Pi approved-plan continuation, but stop sending it as an immediate followUp from agent_end.
• Wait until Pi reports the session is idle, then send the continuation as a normal extension user message.
• Cap the wait at 10 seconds so the extension cannot poll forever.

Background

#804 fixed an approval-path crash in the Pi extension. Approved plans return terminate: true, then Plannotator sends a small continuation message so Pi starts executing the approved plan:

pi.sendUserMessage("Continue with the approved plan.");

That direct call was unsafe from inside the agent_end handler because Pi can still consider the agent run active while agent_end extension listeners are settling. #805 fixed the crash by sending the continuation as:

pi.sendUserMessage("Continue with the approved plan.", { deliverAs: "followUp" });

That keeps execution working, but it has a UI side effect in current Pi TUI: the continuation is rendered as a queued pending message even though the approved plan is already starting:

Follow-up: Continue with the approved plan.
↳ Alt+Up to edit all queued messages

This is confusing because users see a pending follow-up while the agent is already working.

Why this approach

I checked the current Pi source instead of relying on observed behavior:

• agent_end is emitted before the run is fully idle; isStreaming remains true until awaited agent_end listeners settle.
• sendUserMessage() without deliverAs throws while streaming.
• deliverAs: "followUp" pushes the text into Pi's follow-up queue, and the interactive UI renders queued follow-ups with the Follow-up: prefix.

So the extension needs to avoid both extremes:

1. Sending immediately without deliverAs can recreate Pi extension errors after approving a plan #804.
2. Sending immediately with deliverAs: "followUp" creates the visible queued-message row.

The smallest plugin-side solution is to defer the continuation until Pi reports idle, then send a normal user message. That starts the implementation turn without using the visible follow-up queue.

The polling is bounded at 200 attempts × 50ms = 10 seconds. If Pi never becomes idle, Plannotator stops waiting instead of looping forever or creating a stale follow-up queue entry.

Testing

• git diff --check
• Manual local Pi extension test:
  • Approve plan in browser.
  • Agent continues with Continue with the approved plan. as a normal message.
  • No persistent Follow-up: Continue with the approved plan. pending row remains.
• Not run: bun run typecheck (Bun is not installed in this environment: bun: command not found).

[backnotprop]

This is now released in v0.19.27. Thanks for your contribution!