Fix: stop full document saves from writing file path columns

A full save() of a Document instance loaded before another process moved its file wrote the old filename back. The DB then pointed at a path that no longer existed, and recovery only worked when the recomputed path happened to match the file's real location.

Document.save() now leaves filename and archive_filename out of full saves on existing rows. Writers that own those columns opt in with write_file_paths=True or an explicit update_fields. A full save of a row deleted elsewhere now raises instead of re-inserting it.

src/documents/consumer.py

@@ -762,7 +762,7 @@ class ConsumerPlugin(
                         # Don't save with the lock active. Saving will cause the file
                         # renaming logic to acquire the lock as well.
                         # This triggers things like file renaming
-                        document.save()
+                        document.save(write_file_paths=True)
 
                         if document.root_document_id:
                             document_updated.send(