fix(pi-task): serialize state updates and remind about open tasks

pi/extensions/pi-task/state.test.ts

@@ -0,0 +1,47 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+import { TaskStore, restoreTasks, type Task } from "./state.ts";
+
+const active: Task[] = [{ text: "Build feature", status: "in_progress" }];
+const done: Task[] = [{ text: "Build feature", status: "completed" }];
+const result = (tasks: Task[], isError = false) => ({
+  type: "message", message: { role: "toolResult", toolName: "task", isError, details: { tasks } },
+});
+
+test("restores the last valid snapshot on the active branch, including a clear", () => {
+  assert.deepEqual(restoreTasks([result(active), result(done, true), result(done)]), done);
+  assert.deepEqual(restoreTasks([result(active), result([])]), []);
+  assert.deepEqual(restoreTasks([result(active), {
+    type: "message", message: { role: "toolResult", toolName: "task", details: { tasks: [{ text: "bad", status: "invalid" }] } },
+  }]), active);
+});
+
+test("serializes concurrent updates and returns independent snapshots", async () => {
+  const store = new TaskStore();
+  const first = store.call(active);
+  const second = store.call(done);
+  assert.deepEqual(await first, { tasks: active, wasComplete: false });
+  assert.deepEqual(await second, { tasks: done, wasComplete: false });
+  assert.deepEqual(store.read(), done);
+  const snapshot = store.read();
+  snapshot[0].text = "changed";
+  assert.deepEqual(store.read(), done);
+});
+
+test("rejects invalid and cancelled calls without changing state", async () => {
+  const store = new TaskStore();
+  await store.call(active);
+  await assert.rejects(store.call([{ text: "  ", status: "pending" }]), /empty/);
+  const controller = new AbortController();
+  controller.abort();
+  await assert.rejects(store.call(done, controller.signal), /cancelled/);
+  assert.deepEqual(store.read(), active);
+});
+
+test("rejects queued calls after a branch change", async () => {
+  const store = new TaskStore();
+  const queued = store.call(done);
+  store.restore([result(active)]);
+  await assert.rejects(queued, /session changed/);
+  assert.deepEqual(store.read(), active);
+});