feat(coder): v2.6 Phase 3 — lifecycle hardening (idle evict, crash recovery, worktree reaper)

Idle TTL eviction per (chat,agent) + LRU cap (never a busy backend); pure lifecycle-decisions.ts (TDD). Crash recovery lifts openchamber's health-monitor + busy-aware-restart + stale-grace state machine into opencode-server.ts (+ port reclaim) and warm-acp.ts; opencode crash -> fresh sessions, ACP -> re-session/new. F.1 turn-guard + U.6 usage preserved (their tests pass). Orphan worktree reaper (1h grace, superset-style dirty/unpushed preflight, Paseo soft-delete) + close hooks + diff re-baseline after apply_pending. 35 new tests + DB-opt-in reconnect test; 215 coder tests pass; tsc + build clean. Completes v2.6. Follow-ups out of scope: apps/server close-hook caller, 3.7 DiffPanel staging hint, live smokes.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/coder/src/services/backends/warm-acp.ts

@@ -132,6 +132,12 @@ export class WarmAcpBackend implements AgentBackend {
     return this.up ? 'up' : 'down';
   }
 
+  /** Phase 3: busy iff this backend's single session has an in-flight turn. The
+   *  pool reads this to skip idle/LRU eviction (never kill the child mid-prompt). */
+  isBusy(): boolean {
+    return this.activeTurn != null;
+  }
+
   // ─── warm-process lifecycle (2.1 spawn + initialize + session/new ONCE) ───────
 
   /** Lazy: spawn the warm process on first use. Idempotent — one process per backend. */