fix(event-sourced-state): preserve updated_at in todo-add projection

docs/development/bugs/event-sourced-updated-at-drop.md

@@ -0,0 +1,22 @@
+# Resolved: `_todo_from_added_event` 丢弃 `updated_at`
+
+**状态**：已修复（PR #3359，回归测试已转绿）。
+
+## 问题
+
+`_todo_from_added_event` 的构造字典漏拷贝 `updated_at`。生产端 `event_writeback.py` 在
+`TODO_ADDED` payload 中始终写入该字段，读取端 `render_todo_markdown` 与
+`management_projection` 又消费它；reducer 漏拷贝使新增 todo 投影丢失最后活动时间，
+破坏「生产者写入 → 投影 → 消费者读取」的保真不变量。
+
+## 修复
+
+构造字典补入 `"updated_at": compact_text(payload.get("updated_at"))`，归一化与完成事件
+reducer 一致。缺省时 `compact_text(None)` 为空串，读取端
+`todo.get("updated_at") or todo.get("latest_event_at")` 的 fallback 不变。
+
+## 回归测试
+
+`test_updated_at_survives_todo_add_projection`
+（`tests/control_plane/test_todo_mutation_authority.py`）—— 走真实 `TODO_ADDED` 事件 +
+`build_state_projection`，断言投影保留时间戳。

loopx/event_sourced_state.py

@@ -661,6 +661,7 @@ def _todo_from_added_event(event: dict[str, Any]) -> dict[str, Any]:
         "planner_order": payload.get("planner_order"),
         "append_sequence": event.get("append_sequence"),
         "last_event_id": event.get("event_id"),
+        "updated_at": compact_text(payload.get("updated_at")),
     }
     if task_class:
         todo["task_class"] = task_class

tests/control_plane/test_todo_mutation_authority.py

@@ -1311,6 +1311,28 @@ def test_task_domain_survives_markdown_event_projection() -> None:
     assert projection["agent_todos"]["items"][0]["task_domain"] == "validation"
 
 
+def test_updated_at_survives_todo_add_projection() -> None:
+    added = make_state_event(
+        event_id="evt-updated-at-add",
+        goal_id=GOAL_ID,
+        event_type=TODO_ADDED,
+        refs={"todo_id": "todo_updated_at001"},
+        payload={
+            "role": "agent",
+            "title": "Validate one adaptive lane.",
+            "updated_at": "2026-07-18T00:00:00+00:00",
+        },
+        recorded_at="2026-07-18T00:00:00+00:00",
+    )
+
+    projection = build_state_projection([added])
+
+    assert (
+        projection["agent_todos"]["items"][0]["updated_at"]
+        == "2026-07-18T00:00:00+00:00"
+    )
+
+
 def test_task_domain_event_update_is_normalized_and_invalid_values_fail() -> None:
     added = make_state_event(
         event_id="evt-domain-add",