fix: document tidy crashes on a duplicate with NULL timestamps (#1772)

tests/test_document_tidy_null_timestamp.py

@@ -0,0 +1,60 @@
+"""run_document_tidy must not crash when a duplicate has NULL timestamps.
+
+The duplicate-keeper sort used key=(real_len, updated_at or created_at). When
+two duplicates tie on real length and one has both timestamps NULL, Python
+compared None against a datetime and raised TypeError, aborting the entire
+tidy run. The sort key is now total-order safe.
+"""
+import asyncio
+import tempfile
+import uuid
+from datetime import datetime
+
+import pytest
+from sqlalchemy import create_engine
+from sqlalchemy.orm import sessionmaker
+from sqlalchemy.pool import NullPool
+
+import core.database as cdb
+from core.database import Document
+
+
+@pytest.fixture
+def db_factory(monkeypatch):
+    tmp = tempfile.NamedTemporaryFile(suffix=".db", delete=False)
+    engine = create_engine(f"sqlite:///{tmp.name}", connect_args={"check_same_thread": False}, poolclass=NullPool)
+    cdb.Base.metadata.create_all(engine)
+    TS = sessionmaker(bind=engine, autoflush=False, autocommit=False)
+    monkeypatch.setattr(cdb, "SessionLocal", TS)
+    return TS
+
+
+def test_tidy_survives_duplicate_with_null_timestamps(db_factory):
+    content = "This is a real document body long enough to survive junk rules."
+    db = db_factory()
+    try:
+        # Same title + content => same dedup group, equal real length.
+        db.add(Document(id=str(uuid.uuid4()), owner="alice", title="My Report",
+                        current_content=content, updated_at=None, created_at=None))
+        db.add(Document(id=str(uuid.uuid4()), owner="alice", title="My Report",
+                        current_content=content,
+                        updated_at=datetime(2026, 6, 1, 9, 0), created_at=datetime(2026, 6, 1, 9, 0)))
+        db.commit()
+    finally:
+        db.close()
+
+    # Old code raised TypeError (None vs datetime) and aborted.
+    result = asyncio.run(run_tidy())
+    assert isinstance(result, str)
+
+    db = db_factory()
+    try:
+        remaining = db.query(Document).filter(Document.owner == "alice").count()
+        assert remaining == 1  # one duplicate kept, the other removed
+    finally:
+        db.close()
+
+
+async def run_tidy():
+    from src.document_actions import run_document_tidy
+    return await run_document_tidy("alice")