Once support to read from the cu_useragent table and the agent_id columns has been added to all CheckUser interfaces and T361198: Create a maintenance script to populate the cu_useragent table and agent_id columns with values from the agent columns is complete and added to update.php, extension.json should be updated to indicate that the interfaces should read the user agent string from the cu_useragent table.

Acceptance criteria

• The schema migration config added in T361173 should be updated to SCHEMA_COMPAT_NEW | SCHEMA_COMPAT_WRITE_OLD in extension.json