[verified] feat: support monthly completion recurrence

tests/test_after_completion_recurrence.py

@@ -48,7 +48,7 @@ def test_dst_gap_rolls_forward_and_ambiguous_time_uses_first_fold():
         due_has_time=True,
     )
     gap_due = recurrence_service._after_completion_due(
-        gap_task, datetime(2026, 3, 7, 15, tzinfo=UTC), 1, user
+        gap_task, datetime(2026, 3, 7, 15, tzinfo=UTC), 1, "days", user
     )
     assert gap_due == datetime(2026, 3, 8, 7, 30, tzinfo=UTC)  # local 03:30 after gap
 
@@ -60,7 +60,7 @@ def test_dst_gap_rolls_forward_and_ambiguous_time_uses_first_fold():
         due_has_time=True,
     )
     fold_due = recurrence_service._after_completion_due(
-        fold_task, datetime(2026, 10, 31, 15, tzinfo=UTC), 1, user
+        fold_task, datetime(2026, 10, 31, 15, tzinfo=UTC), 1, "days", user
     )
     assert fold_due == datetime(2026, 11, 1, 5, 30, tzinfo=UTC)  # first 01:30, fold=0
 
@@ -89,6 +89,30 @@ def test_user_timezone_is_the_calendar_contract_for_after_completion(client, mon
     assert datetime.fromisoformat(completed.json()["due_at"]) == datetime(2026, 3, 9, 9, 30, tzinfo=UTC)
 
 
+def test_month_interval_uses_calendar_month_clamping(client, monkeypatch):
+    inbox = boot(client)
+    task = create_after_completion_task(
+        client,
+        inbox,
+        due_at="2026-01-31T01:30:00Z",
+        after_completion_days=1,
+        after_completion_unit="months",
+    ).json()
+    monkeypatch.setattr(
+        "backend.recurrence_service.utcnow",
+        lambda: datetime(2026, 1, 30, 16, 30, tzinfo=UTC),  # 2026-01-31 00:30 Asia/Shanghai
+    )
+
+    completed = client.patch(
+        f"/api/v1/tasks/{task['id']}", json={"completed": True, "version": task["version"]}
+    )
+
+    assert completed.status_code == 200
+    assert datetime.fromisoformat(completed.json()["due_at"]) == datetime(2026, 2, 28, 1, 30, tzinfo=UTC)
+    recurrence = client.get(f"/api/v1/tasks/{task['id']}/recurrence").json()
+    assert recurrence["after_completion_unit"] == "months"
+
+
 def test_atomic_task_create_and_read_after_completion_recurrence(client):
     inbox = boot(client)
 
@@ -105,6 +129,7 @@ def test_atomic_task_create_and_read_after_completion_recurrence(client):
         "ends_at": None,
         "trigger_mode": "after_completion",
         "after_completion_days": 2,
+        "after_completion_unit": "days",
         "last_completed_at": None,
     }
 
@@ -122,6 +147,8 @@ def test_after_completion_configuration_validation(client):
         {"title": "零天", "list_id": inbox["id"], "due_at": "2026-03-08T01:30:00Z", "trigger_mode": "after_completion", "after_completion_days": 0},
         {"title": "太长", "list_id": inbox["id"], "due_at": "2026-03-08T01:30:00Z", "trigger_mode": "after_completion", "after_completion_days": 3651},
         {"title": "子任务", "list_id": inbox["id"], "parent_id": child["id"], "due_at": "2026-03-08T01:30:00Z", "trigger_mode": "after_completion", "after_completion_days": 1},
+        {"title": "只有单位", "list_id": inbox["id"], "due_at": "2026-03-08T01:30:00Z", "after_completion_unit": "months"},
+        {"title": "定期带月份", "list_id": inbox["id"], "due_at": "2026-03-08T01:30:00Z", "trigger_mode": "scheduled", "rrule": "FREQ=DAILY", "after_completion_unit": "months"},
     ]
     for payload in invalid_payloads:
         assert client.post("/api/v1/tasks", json=payload).status_code in {400, 422}