ACP misses autonomous harness turns because event subscription is prompt-scoped

Summary

The kimi-code ACP server does not forward session/update notifications for turns started autonomously by the harness. Examples include background-task completion injections, system-reminder-only turns, and cron fires.

Affected version

Verified in kimi-code 0.38.0, published 2026-08-20. The same behavior exists in local 0.34.0.

SHA256 for the checked 0.38.0 Linux x64 binary:
7f18b701ea751d14bf051776747ca0339f8d59693aec9051276933067a914b00

Evidence

The embedded ACP server code in both versions has this structure:

prompt() calls runTurnBody(...)
runTurnBody creates:
  const unsub = this.session.onEvent((event) => { ... })
runTurnBody unsubscribes when the prompt turn settles

There is no persistent per-session harness-event subscription. Therefore, when no client prompt request is active, autonomous harness events have no subscription that can forward them as ACP session/update notifications.

Expected behavior

A connected ACP client receives session/update notifications whenever the session produces main-agent events, including events from autonomous harness turns. ACP session updates are not limited to a prompt request lifetime.

Actual behavior

Autonomous turns produce no ACP session/update notifications. A client that is waiting for background activity cannot display the assistant output or the turn boundaries.

Minimal fix proposal

Create one persistent main-agent event subscription when the ACP session is created or loaded. Forward those events to conn.sessionUpdate unconditionally. Keep runTurnBody responsible only for settlement of its own prompt request, such as resolving on that prompt's turn.ended event.

This preserves prompt request semantics while allowing session updates at any time.

Reproduction

1. Start kimi-code in ACP mode.
2. Establish an ACP session and keep the connection open.
3. Trigger a harness action that starts a turn without an active client prompt, such as a background-task completion injection or cron fire.
4. Observe that no session/update notification arrives for the autonomous turn.
5. Compare with a normal client prompt, where updates arrive while runTurnBody has subscribed.

Please let me know if you need the binary extraction details or a small ACP client trace.

Start at the ACP server's prompt() and runTurnBody path, then trace session creation or loading and the existing session.onEvent subscription. Reproduce the issue with an autonomous harness turn while no prompt is active, and compare it with a normal prompt. Done means connected clients receive session/update notifications for autonomous turns without changing prompt settlement behavior.