fix(agent): reject ambiguous duplicate todo identities

apps/agent/src/todos.py

@@ -20,6 +20,11 @@ def manage_todos(todos: list[Todo], runtime: ToolRuntime) -> Command:
     """
     Manage the current todos.
     """
+    # Validate supplied IDs before assigning any missing IDs or updating state.
+    supplied_ids = [todo["id"] for todo in todos if todo.get("id")]
+    if len(supplied_ids) != len(set(supplied_ids)):
+        raise ValueError("Todo IDs must be unique; give each item a distinct ID.")
+
     # Ensure all todos have IDs that are unique
     for todo in todos:
         if "id" not in todo or not todo["id"]:

apps/agent/tests/test_todo_unique_ids_regression.py

@@ -0,0 +1,37 @@
+from copy import deepcopy
+
+import pytest
+from langchain.tools import ToolRuntime
+
+from src.todos import manage_todos
+
+
+def runtime():
+    return ToolRuntime(state={"messages": [], "todos": []}, context=None, config={},
+                       stream_writer=lambda _: None, tool_call_id="todo-call", store=None)
+
+
+def todo(id, title):
+    return {"id": id, "title": title, "description": "", "emoji": "", "status": "pending"}
+
+
+def test_duplicate_supplied_ids_are_rejected_before_state_update():
+    items = [todo("", "New"), todo("same", "First"), todo("same", "Second")]
+    original = deepcopy(items)
+    with pytest.raises(ValueError, match="unique"):
+        manage_todos.func(items, runtime())
+    assert items == original
+
+
+def test_unique_supplied_ids_are_stable_in_state_update():
+    items = [todo("one", "First"), todo("two", "Second")]
+    result = manage_todos.func(items, runtime())
+    assert result.update["todos"] == items
+    assert result.update["messages"][0].tool_call_id == "todo-call"
+
+
+def test_new_todos_receive_distinct_nonempty_ids():
+    result = manage_todos.func([todo("", "First"), todo("", "Second")], runtime())
+    ids = [item["id"] for item in result.update["todos"]]
+    assert all(ids)
+    assert len(set(ids)) == 2