To enforce the API contract that the client never performs any stable writes to an unpublished table, we need to add a check to __disagg_shared_metadata_op that ensures that the table already exists in the shared metadata table if the requested operation is (WT_SHARED_METADATA_UPDATE. If the check fails, WiredTiger should panic. This mechanism is far from perfect, but it will still provide the guarantee that we will never complete a checkpoint with stable data in an unpublished table.