fix: persist cleared knowledge collection timestamps

backend/app/schemas/catalog.py

@@ -41,8 +41,7 @@ class Patch(Input):
     @classmethod
     def disallow_required_null(cls, value, info):
         if (
-            info.field_name
-            in {"name", "title", "category", "content", "notes", "collected_at", "expected_version"}
+            info.field_name in {"name", "title", "category", "content", "notes", "expected_version"}
             and value is None
         ):
             raise ValueError("该字段不能为 null")
@@ -92,6 +91,13 @@ class DocumentUpdate(Patch):
     collected_at: AwareDatetime | None = None
     notes: Notes | None = None
 
+    @field_validator("collected_at", mode="before")
+    @classmethod
+    def collection_time_is_required(cls, value):
+        if value is None:
+            raise ValueError("文档采集时间不能为 null")
+        return value
+
 
 class DocumentRead(Read):
     source_id: int

backend/tests/test_catalog.py

@@ -156,6 +156,52 @@ def test_review_edit_and_history(client):
     assert events["items"][1]["snapshot"]["item"]["verification_status"] == "verified"
 
 
+def test_clear_knowledge_collection_time_requires_new_evidence(client):
+    verified = review(client, knowledge(client)).json()
+    path = f"/api/knowledge/{verified['id']}"
+    before = client.get(path + "/history").json()["items"]
+
+    response = client.patch(
+        path, json={"expected_version": verified["version"], "collected_at": None}
+    )
+
+    assert response.status_code == 200
+    cleared = response.json()
+    assert cleared["collected_at"] is None
+    assert cleared["version"] == verified["version"] + 1
+    assert cleared["verification_status"] == "pending"
+    assert cleared["reviewer"] is None and cleared["reviewed_at"] is None
+    assert cleared["verification_notes"] is None
+    assert review(client, cleared).status_code == 422
+    assert client.get(path).json() == cleared
+    events = client.get(path + "/history").json()["items"]
+    assert events[0]["snapshot"]["item"]["collected_at"] is None
+    assert events[1:] == before
+    assert (
+        client.patch(
+            path, json={"expected_version": verified["version"], "collected_at": COLLECTED}
+        ).status_code
+        == 409
+    )
+
+    restored = client.patch(
+        path, json={"expected_version": cleared["version"], "collected_at": COLLECTED}
+    ).json()
+    assert review(client, restored).status_code == 200
+
+
+def test_document_collection_time_cannot_be_cleared(client):
+    doc = document(client, source(client)["id"])
+    path = f"/api/documents/{doc['id']}"
+    before = client.get(path + "/history").json()
+
+    response = client.patch(path, json={"expected_version": doc["version"], "collected_at": None})
+
+    assert response.status_code == 422
+    assert client.get(path).json() == doc
+    assert client.get(path + "/history").json() == before
+
+
 def test_source_document_changes_invalidate_evidence(client):
     src = source(client)
     doc = document(client, src["id"])