fix: make session resume atomic across restarts

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

@@ -84,6 +84,36 @@ function recordingChild() {
   return ch;
 }
 
+test("createFor kills a spawned child when post-spawn initialization throws", () => {
+  const child = recordingChild();
+  child.kill = vi.fn();
+  child.stdout = {
+    on: () => { throw new Error("READER_INIT_SENTINEL"); },
+  };
+  const mgr = new PiProcessManager(loadConfig({}), { spawnFn: () => child as any });
+
+  expect(() => mgr.createFor("broken-init", {})).toThrow("READER_INIT_SENTINEL");
+
+  expect(child.kill).toHaveBeenCalledOnce();
+  expect(mgr.get("broken-init")).toBeUndefined();
+  expect(mgr.count()).toBe(0);
+});
+
+test("createFor kills a spawned child when spawn boundary initialization throws", () => {
+  const child = recordingChild();
+  child.kill = vi.fn();
+  child.stderr = {
+    on: () => { throw new Error("STDERR_INIT_SENTINEL"); },
+  };
+  const mgr = new PiProcessManager(loadConfig({}), { spawnFn: () => child as any });
+
+  expect(() => mgr.createFor("broken-spawn-init", {})).toThrow("STDERR_INIT_SENTINEL");
+
+  expect(child.kill).toHaveBeenCalledOnce();
+  expect(mgr.get("broken-spawn-init")).toBeUndefined();
+  expect(mgr.count()).toBe(0);
+});
+
 test("un exit INATTESO del child notifica il client (info error + agent_end)", async () => {
   const cfg = loadConfig({});
   const child = recordingChild();