fix: close Pi subagent review gaps

electron/coding-runtime/pi/subagent.ts

@@ -353,8 +353,12 @@ export class PiSubagentScheduler {
     let child: PiSubagentChild | undefined;
     try {
       releaseChild = await this.childPermits.acquire(record.controller.signal);
-      await this.reclaimIdleCapacity(record.controller.signal);
-      processLease = await this.processBudget.acquire(record.controller.signal);
+      const budgetWasFull = this.processBudget.activeCount >= this.processBudget.maxProcesses;
+      const processLeaseFlight = this.processBudget.acquire(record.controller.signal, 'child');
+      if (budgetWasFull && this.reclaimProcessCapacity) {
+        await this.reclaimProcessCapacity();
+      }
+      processLease = await processLeaseFlight;
       if (record.controller.signal.aborted) throw new PiSubagentChildError('SUBAGENT_ABORTED');
       projected.status = 'running';
       this.emit(details, onUpdate);
@@ -391,14 +395,6 @@ export class PiSubagentScheduler {
     }
   }
 
-  private async reclaimIdleCapacity(signal: AbortSignal): Promise<void> {
-    while (!signal.aborted
-      && this.processBudget.activeCount >= this.processBudget.maxProcesses
-      && this.reclaimProcessCapacity) {
-      if (!await this.reclaimProcessCapacity()) break;
-    }
-  }
-
   private markRemaining(
     details: SubagentDetailsV1,
     from: number,

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

@@ -116,6 +116,7 @@ export interface PiProcessLease {
 
 interface PiProcessBudgetWaiter {
   signal?: AbortSignal;
+  priority: 'normal' | 'child';
   resolve(lease: PiProcessLease): void;
   reject(error: Error): void;
   onAbort?: () => void;
@@ -134,11 +135,19 @@ export class PiProcessBudget {
   get activeCount(): number { return this.active; }
   get waitingCount(): number { return this.waiters.length; }
 
-  acquire(signal?: AbortSignal): Promise<PiProcessLease> {
+  acquire(
+    signal?: AbortSignal,
+    priority: 'normal' | 'child' = 'normal',
+  ): Promise<PiProcessLease> {
     if (signal?.aborted) return Promise.reject(new Error('Pi process budget acquisition cancelled'));
     if (this.active < this.maxProcesses) return Promise.resolve(this.issueLease());
     return new Promise<PiProcessLease>((resolve, reject) => {
-      const waiter: PiProcessBudgetWaiter = { resolve, reject, ...(signal ? { signal } : {}) };
+      const waiter: PiProcessBudgetWaiter = {
+        resolve,
+        reject,
+        priority,
+        ...(signal ? { signal } : {}),
+      };
       if (signal) {
         waiter.onAbort = () => {
           const index = this.waiters.indexOf(waiter);
@@ -166,7 +175,9 @@ export class PiProcessBudget {
 
   private advance(): void {
     while (this.active < this.maxProcesses && this.waiters.length > 0) {
-      const waiter = this.waiters.shift() as PiProcessBudgetWaiter;
+      const childIndex = this.waiters.findIndex(({ priority }) => priority === 'child');
+      const [waiter] = this.waiters.splice(childIndex >= 0 ? childIndex : 0, 1);
+      if (!waiter) return;
       if (waiter.onAbort && waiter.signal) {
         waiter.signal.removeEventListener('abort', waiter.onAbort);
       }

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

@@ -65,7 +65,9 @@ export type PiWorkerProcessOptions = {
 export function buildPiRpcArgs(
   sessionDir: string,
   additionalArgs: readonly string[] = [],
-  tools: readonly string[] = ['read', 'bash', 'edit', 'write', 'grep', 'find', 'ls', 'ask_user'],
+  tools: readonly string[] = [
+    'read', 'bash', 'edit', 'write', 'grep', 'find', 'ls', 'ask_user', 'subagent',
+  ],
 ): string[] {
   return [
     '--mode', 'rpc',