Pi integration: track async subagent lifecycle for working/idle state

[desideratum]

Summary

The Pi integration (herdr-agent-state.ts, integration version 3) does not track async subagent lifecycle. When a Pi session dispatches an async subagent via nicobailon/pi-subagents (the most widely used Pi subagent package), the parent agent's agent_end event fires immediately after dispatch, causing herdr to transition the pane to idle — even though the async subagent is still executing in the background.

Current behavior

The Pi integration hooks only Pi core lifecycle events: agent_start, agent_end, session_start, session_shutdown, plus a custom herdr:blocked event. When the parent Pi agent finishes its turn after dispatching an async subagent, agent_end fires, and herdr shows the pane as idle (after the 250ms debounce). The async subagent runs in a detached child process with no corresponding events visible to the integration.

Expected behavior

The pane should show as working while one or more async subagents are running, and transition to idle only when all async runs have completed (or failed/paused).

Available events

The nicobailon/pi-subagents extension already emits lifecycle events on pi.events:

• subagent:async-started — fired when an async run launches
• subagent:async-complete — fired when an async run finishes
• subagent:control-event — fired on control state changes (e.g., needs_attention)

These are defined in pi-subagents/src/shared/types.ts and consumed internally by pi-subagents' own async job tracker. They are available to any Pi extension that subscribes via pi.events.on().

Suggested approach

The integration already uses a counter pattern for blocked state (blockedCount). A similar asyncRunCount incremented on subagent:async-started and decremented on subagent:async-complete would feed into desiredState() to keep the pane in working while async runs are active. The subagent:control-event could optionally surface needs_attention as blocked.

This mirrors the approach already taken for Claude Code (subagent hook events, #198) and OpenCode (subagent permission prompts as blocked, #838).

Environment

• herdr: stable channel, current release
• Pi: v0.80.x (Homebrew)
• pi-subagents (nicobailon/pi-subagents): v0.31.x
• macOS

[vekexasia]

I would like this as well.