fix: close Pi subagent review gaps

tests/unit/pi-subagent.test.ts

@@ -213,7 +213,13 @@ describe('Pi subagent scheduler', () => {
     const processBudget = new PiProcessBudget(2);
     const firstParent = await processBudget.acquire();
     const idleParent = await processBudget.acquire();
+    let waitingParentSettled = false;
+    const waitingParent = processBudget.acquire().then((lease) => {
+      waitingParentSettled = true;
+      return lease;
+    });
     let reclaimed = 0;
+    let childRanBeforeWaitingParent = false;
     const scheduler = new PiSubagentScheduler({
       processBudget,
       reclaimProcessCapacity: async () => {
@@ -223,7 +229,10 @@ describe('Pi subagent scheduler', () => {
       },
       openChild: async (input) => ({
         id: input.taskId,
-        async run() { return { summary: 'done' }; },
+        async run() {
+          childRanBeforeWaitingParent = !waitingParentSettled;
+          return { summary: 'done' };
+        },
         async stop() {},
       }),
     });
@@ -234,8 +243,12 @@ describe('Pi subagent scheduler', () => {
       details: { tasks: [{ status: 'complete' }] },
     });
     expect(reclaimed).toBe(1);
-    expect(processBudget.activeCount).toBe(1);
+    expect(childRanBeforeWaitingParent).toBe(true);
+    const waitingParentLease = await waitingParent;
+    expect(processBudget.activeCount).toBe(2);
+    waitingParentLease.release();
     firstParent.release();
+    expect(processBudget.activeCount).toBe(0);
     await scheduler.close();
   });
 });