Function warn_on_glue_compatibility_mismatch 

async fn warn_on_glue_compatibility_mismatch(
    client: &Client,
    registry_name: &str,
    schema_name: &str,
    desired: Option<&Compatibility>,
)

Warn if the schema’s existing compatibility differs from desired.

Best-effort and advisory only: a failed read is logged and ignored. The sink never changes an existing schema’s compatibility (see publish_glue_schema), so a mismatch is surfaced for the operator, not acted on.