feat: add task and habit reordering

tests/test_app.py

@@ -92,6 +92,41 @@ def test_task_can_be_updated_completed_and_soft_deleted(client):
     assert client.get("/api/v1/tasks").json()["items"] == []
 
 
+def test_reorder_tasks_persists_top_level_and_subtask_order(client):
+    client = initialized_client(client)
+    inbox = client.get("/api/v1/lists").json()[0]
+    first = client.post("/api/v1/tasks", json={"title": "第一个", "list_id": inbox["id"]}).json()
+    second = client.post("/api/v1/tasks", json={"title": "第二个", "list_id": inbox["id"]}).json()
+    child_a = client.post(
+        "/api/v1/tasks", json={"title": "子任务 A", "list_id": inbox["id"], "parent_id": first["id"]}
+    ).json()
+    child_b = client.post(
+        "/api/v1/tasks", json={"title": "子任务 B", "list_id": inbox["id"], "parent_id": first["id"]}
+    ).json()
+
+    top_level = client.put("/api/v1/tasks/reorder", json={"task_ids": [second["id"], first["id"]]})
+    assert top_level.status_code == 204
+    children = client.put("/api/v1/tasks/reorder", json={"task_ids": [child_b["id"], child_a["id"]]})
+    assert children.status_code == 204
+
+    client.post("/api/v1/tasks", json={"title": "第三个", "list_id": inbox["id"]})
+    listed = client.get("/api/v1/tasks", params={"list_id": inbox["id"], "page": 1}).json()["items"]
+    assert [task["title"] for task in listed] == ["第二个", "第一个", "第三个"]
+    assert [task["title"] for task in listed[1]["subtasks"]] == ["子任务 B", "子任务 A"]
+
+
+def test_reorder_tasks_rejects_mixed_parent_scopes(client):
+    client = initialized_client(client)
+    inbox = client.get("/api/v1/lists").json()[0]
+    parent = client.post("/api/v1/tasks", json={"title": "父任务", "list_id": inbox["id"]}).json()
+    child = client.post(
+        "/api/v1/tasks", json={"title": "子任务", "list_id": inbox["id"], "parent_id": parent["id"]}
+    ).json()
+
+    response = client.put("/api/v1/tasks/reorder", json={"task_ids": [parent["id"], child["id"]]})
+    assert response.status_code == 400
+
+
 def test_task_update_rejects_null_title(client):
     client.post(
         "/api/v1/setup/initialize",