feat: add task duration tracking

tests/state.test.ts

@@ -68,6 +68,144 @@ test("enforces done descendants against the final atomic update state", () => {
   assert.deepEqual(state.list().map((task) => task.status), ["in-progress", "in-progress"]);
 });
 
+test("preserves and accumulates timing across repeated updates and status changes", () => {
+  const startedAt = Date.UTC(2026, 0, 1);
+  let now = startedAt;
+  const state = new TaskState(() => now);
+
+  const [started] = state.add([{ name: "Timed", status: "in-progress" }]);
+  assert.equal(started?.startedAt, new Date(startedAt).toISOString());
+  assert.equal(started?.stoppedAt, undefined);
+  assert.equal(started?.durationMs, 0);
+
+  now += 5_000;
+  const [repeated] = state.update([{ id: 1, name: "Renamed", status: "in-progress" }]);
+  assert.equal(repeated?.startedAt, started?.startedAt);
+  assert.equal(repeated?.stoppedAt, undefined);
+  assert.equal(repeated?.durationMs, 5_000);
+
+  now += 2_000;
+  const [paused] = state.update([{ id: 1, status: "blocked" }]);
+  assert.equal(paused?.startedAt, started?.startedAt);
+  assert.equal(paused?.stoppedAt, new Date(now).toISOString());
+  assert.equal(paused?.durationMs, 7_000);
+
+  now += 10_000;
+  assert.equal(state.get([1])[0]?.durationMs, 7_000);
+  const [resumed] = state.update([{ id: 1, status: "in-progress" }]);
+  assert.equal(resumed?.startedAt, started?.startedAt);
+  assert.equal(resumed?.stoppedAt, undefined);
+  assert.equal(resumed?.durationMs, 7_000);
+
+  now += 3_000;
+  const [done] = state.update([{ id: 1, status: "done" }]);
+  assert.equal(done?.startedAt, started?.startedAt);
+  assert.equal(done?.stoppedAt, new Date(now).toISOString());
+  assert.equal(done?.durationMs, 10_000);
+  assert.deepEqual(state.snapshot().timings, [
+    { taskId: 1, startedAt, stoppedAt: now, accumulatedMs: 10_000 },
+  ]);
+});
+
+test("does not stop a timer when an atomic update fails", () => {
+  const startedAt = Date.UTC(2026, 0, 1);
+  let now = startedAt;
+  const state = new TaskState(() => now);
+  state.add([
+    {
+      name: "Parent",
+      status: "in-progress",
+      children: [{ name: "Unfinished child" }],
+    },
+  ]);
+
+  now += 5_000;
+  assert.throws(() => state.update([{ id: 1, status: "done" }]), /unfinished descendants/);
+  const afterFailure = state.get([1])[0];
+  assert.equal(afterFailure?.stoppedAt, undefined);
+  assert.equal(afterFailure?.durationMs, 5_000);
+
+  now += 2_000;
+  assert.equal(state.get([1])[0]?.durationMs, 7_000);
+});
+
+test("restores timers and starts legacy in-progress snapshots at load time", () => {
+  const startedAt = Date.UTC(2026, 0, 1);
+  let now = startedAt;
+  const source = new TaskState(() => now);
+  source.add([{ name: "Persisted", status: "in-progress" }]);
+  now += 2_500;
+  source.update([{ id: 1, status: "pending" }]);
+
+  now += 20_000;
+  const restored = new TaskState(() => now);
+  restored.restore(source.snapshot());
+  assert.equal(restored.get([1])[0]?.startedAt, new Date(startedAt).toISOString());
+  assert.equal(restored.get([1])[0]?.stoppedAt, new Date(startedAt + 2_500).toISOString());
+  assert.equal(restored.get([1])[0]?.durationMs, 2_500);
+
+  const legacy = new TaskState(() => now);
+  legacy.restore({
+    tasks: [
+      {
+        id: 1,
+        name: "Legacy active",
+        status: "in-progress",
+        parentId: null,
+        childrenIds: [],
+      },
+    ],
+    nextId: 2,
+  });
+  assert.equal(legacy.get([1])[0]?.startedAt, new Date(now).toISOString());
+  assert.equal(legacy.get([1])[0]?.durationMs, 0);
+  assert.equal(legacy.snapshot().timings?.[0]?.activeStartedAt, now);
+});
+
+test("rejects out-of-range persisted timestamps without replacing state", () => {
+  const state = new TaskState(() => 0);
+  state.add([{ name: "Keep" }]);
+  const before = state.snapshot();
+
+  assert.throws(
+    () =>
+      state.restore({
+        tasks: [
+          {
+            id: 1,
+            name: "Corrupt timer",
+            status: "in-progress",
+            parentId: null,
+            childrenIds: [],
+          },
+        ],
+        nextId: 2,
+        timings: [
+          {
+            taskId: 1,
+            startedAt: Number.MAX_SAFE_INTEGER,
+            activeStartedAt: Number.MAX_SAFE_INTEGER,
+            accumulatedMs: 0,
+          },
+        ],
+      }),
+    /startedAt must be a valid non-negative timestamp/,
+  );
+  assert.deepEqual(state.snapshot(), before);
+});
+
+test("finalizes an active timer in removed task details", () => {
+  let now = Date.UTC(2026, 0, 1);
+  const state = new TaskState(() => now);
+  state.add([{ name: "Canceled", status: "in-progress" }]);
+  now += 4_000;
+
+  const [removed] = state.remove([1]);
+  assert.equal(removed?.stoppedAt, new Date(now).toISOString());
+  assert.equal(removed?.durationMs, 4_000);
+  assert.deepEqual(state.list(), []);
+});
+
 test("rejects cycles and duplicate patches without partial changes", () => {
   const state = new TaskState();
   state.add([{ name: "Root", description: "Root", children: [{ name: "Child", description: "Child" }] }]);