feat: add Pi subagent scheduler and child runtime

electron/coding-runtime/pi/worker-pool.ts

@@ -333,6 +333,15 @@ export class PiWorkerPool {
     return record ? this.publicState(record) : null;
   }
 
+  async reclaimIdleWorker(): Promise<boolean> {
+    const record = [...this.workers.values()]
+      .filter((candidate) => candidate.state === 'ready' || candidate.state === 'idle')
+      .sort((left, right) => left.lastUsed - right.lastUsed)[0];
+    if (!record) return false;
+    await this.evict(record);
+    return true;
+  }
+
   subscribe(listener: (event: PiWorkerPoolEvent) => void): () => void {
     this.listeners.add(listener);
     return () => this.listeners.delete(listener);