* fix(server): keep active agent trees resident
Idle collection treated an inactive parent turn as process quiescence even when descendant work was still running. Protect managed and provider-owned subagent trees, carry descendant activity into the idle window, and use a conservative 30-minute fallback.
* fix(server): close idle collection races
Retain managed ancestry across closed intermediates, refresh descendant state after each awaited close, and invalidate running provider subagents when their runtime is terminated.
* fix(server): serialize agent tree collection
Keep ancestors resident until managed descendants are collected, serialize descendant registration with idle collection, and preserve provider subagent state across hot reloads.
* fix(server): retain closed descendant activity
Carry persisted descendant activity through runtime closure, avoid error children pinning parents, and cancel stale provider children when reload replacement aborts.
* test(server): make descendant expiry deterministic
* fix(server): scope idle child protection
* fix(server): tighten idle tree coordination
* fix(server): reduce aggressive idle cleanup
Keep the mitigation conservative: extend the idle timeout without inferring tree liveness from incomplete lifecycle signals.
* fix(server): keep parents alive during child work
Idle cleanup now respects running managed and provider-native children while retaining a conservative 30-minute fallback.
* fix(server): clear running child state on close
* fix(server): drain child events before close
