feat: add SelfHealingManager for unattended multi-day operation

Adds four self-healing subsystems to enable the engine to recover from
common failure modes without human intervention:

- Auto-unpause: clears rate-limit-triggered globalPause with escalating
  backoff (5 min → 60 min cap), resets on sustained recovery
- Stuck kill budget: caps task stuck-kill retries (default 3) to prevent
  infinite stuck→todo→stuck loops
- Periodic maintenance (every 15 min): git worktree prune, orphan cleanup,
  SQLite WAL checkpoint
- Worktree cap enforcement: removes oldest idle worktrees when count
  exceeds 2× maxWorktrees

New settings: autoUnpauseEnabled, autoUnpauseBaseDelayMs,
autoUnpauseMaxDelayMs, maxStuckKills, maintenanceIntervalMs.
New task field: stuckKillCount (schema v8 migration).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/engine/src/runtimes/in-process-runtime.ts

@@ -20,6 +20,7 @@ import type {
 import { runtimeLog } from "../logger.js";
 import type { StuckTaskDetector } from "../stuck-task-detector.js";
 import type { UsageLimitPauser } from "../usage-limit-detector.js";
+import { SelfHealingManager } from "../self-healing.js";
 
 /**
  * InProcessRuntime runs a project within the main process.
@@ -65,6 +66,7 @@ export class InProcessRuntime
   private globalSemaphore?: AgentSemaphore;
   private stuckTaskDetector?: StuckTaskDetector;
   private usageLimitPauser?: UsageLimitPauser;
+  private selfHealingManager?: SelfHealingManager;
   private agentStore?: AgentStore;
   private heartbeatMonitor?: HeartbeatMonitor;
   /** Maps task IDs to agent IDs for lifecycle tracking */
@@ -225,13 +227,19 @@ export class InProcessRuntime
         runtimeLog.warn(`AgentStore initialization failed (continuing without agent monitoring):`, agentErr);
       }
 
-      // 7. Set up event forwarding from TaskStore
+      // 7. Initialize SelfHealingManager
+      this.selfHealingManager = new SelfHealingManager(this.taskStore, {
+        rootDir: this.config.workingDirectory,
+      });
+      this.selfHealingManager.start();
+
+      // 8. Set up event forwarding from TaskStore
       this.setupEventForwarding();
 
-      // 8. Resume orphaned in-progress tasks
+      // 9. Resume orphaned in-progress tasks
       await this.executor.resumeOrphaned();
 
-      // 9. Start scheduler
+      // 10. Start scheduler
       this.scheduler.start();
 
       this.setStatus("active");
@@ -266,13 +274,19 @@ export class InProcessRuntime
     runtimeLog.log(`Stopping InProcessRuntime for project ${this.config.projectId}`);
 
     try {
-      // 1. Stop heartbeat monitor
+      // 1. Stop self-healing manager
+      if (this.selfHealingManager) {
+        this.selfHealingManager.stop();
+        runtimeLog.log("SelfHealingManager stopped");
+      }
+
+      // 2. Stop heartbeat monitor
       if (this.heartbeatMonitor) {
         this.heartbeatMonitor.stop();
         runtimeLog.log("HeartbeatMonitor stopped");
       }
 
-      // 2. Stop scheduler (prevents new task scheduling)
+      // 3. Stop scheduler (prevents new task scheduling)
       if (this.scheduler) {
         this.scheduler.stop();
         runtimeLog.log("Scheduler stopped");