fix: serialize session lifecycle transitions

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

@@ -66,6 +66,27 @@ test("l'exit del VECCHIO child non elimina il nuovo runtime (exit identity-check
   mgr.teardown("respawn-id");
 });
 
+test("identity-checked teardown cannot kill a replacement runtime", () => {
+  const cfg = loadConfig({ THT_HARNESS_DIR: "../harness" });
+  const firstChild = recordingChild();
+  const secondChild = recordingChild();
+  firstChild.kill = vi.fn();
+  secondChild.kill = vi.fn();
+  const children = [firstChild, secondChild];
+  const mgr = new PiProcessManager(cfg, { spawnFn: () => children.shift() as any });
+  const first = mgr.createFor("replace-id", {});
+  mgr.teardown("replace-id");
+  const second = mgr.createFor("replace-id", {});
+
+  expect(mgr.teardownIfCurrent("replace-id", first)).toBe(false);
+  expect(mgr.get("replace-id")).toBe(second);
+  expect(secondChild.kill).not.toHaveBeenCalled();
+
+  expect(mgr.teardownIfCurrent("replace-id", second)).toBe(true);
+  expect(mgr.get("replace-id")).toBeUndefined();
+  expect(secondChild.kill).toHaveBeenCalledOnce();
+});
+
 test("oltre maxPiProcesses solleva errore", async () => {
   const cfg = { ...loadConfig({}), maxPiProcesses: 1 };
   const mgr = new PiProcessManager(cfg, { spawnFn: () => spawn("node", [FAKE, SCRIPT]) as any });