fix: release Pi snapshots on failed initialization

backend/test/pi-process-manager.test.ts

@@ -306,10 +306,18 @@ test("createFor kills a spawned child when post-spawn initialization throws", ()
   child.stdout = {
     on: () => { throw new Error("READER_INIT_SENTINEL"); },
   };
-  const mgr = new PiProcessManager(loadConfig({}), { spawnFn: () => child as any });
+  let snapshotDir: string | undefined;
+  const mgr = new PiProcessManager(loadConfig({}), {
+    spawnFn: (_command, _args, options) => {
+      snapshotDir = options.env.PI_CODING_AGENT_DIR;
+      return child as any;
+    },
+  });
 
   expect(() => mgr.createFor("broken-init", {})).toThrow("READER_INIT_SENTINEL");
 
+  expect(snapshotDir).toBeTruthy();
+  expect(existsSync(snapshotDir!)).toBe(false);
   expect(child.kill).toHaveBeenCalledOnce();
   expect(mgr.get("broken-init")).toBeUndefined();
   expect(mgr.count()).toBe(0);