fix: settle Pi child capacity reservations

tests/unit/pi-worker-pool.test.ts

@@ -227,6 +227,33 @@ describe('Pi worker pool', () => {
     expect(processBudget.activeCount).toBe(0);
   });
 
+  it('releases the process lease even when stopping an idle worker fails', async () => {
+    const processBudget = new PiProcessBudget(1);
+    const pool = new PiWorkerPool({
+      processBudget,
+      maxIdle: 1,
+      openWorker: async ({ conversation: input }) => {
+        const worker = new FakeWorker(`worker-${input.conversationId}`);
+        worker.stop = async () => {
+          worker.stopped = true;
+          throw new Error('stop failed');
+        };
+        return {
+          worker,
+          session: {
+            piSessionId: `session-${input.conversationId}`,
+            sessionKey: `key-${input.conversationId}`,
+          },
+        };
+      },
+    });
+    await pool.prepare(conversation('conversation-stop-failure'));
+
+    await expect(pool.dispose('conversation-stop-failure')).rejects.toThrow('stop failed');
+    expect(processBudget.activeCount).toBe(0);
+    expect(processBudget.waitingCount).toBe(0);
+  });
+
   it('never evicts a running worker when the warm-idle LRU exceeds its cap', async () => {
     const workers = new Map<string, FakeWorker>();
     const pool = new PiWorkerPool({