`D21` reverted the refusal to a failure envelope and had no weaker sibling.
`D21L` keeps the response schema and drops the client's correlation key, which
leaves a refusal the client cannot match to the request that earned it. It
dies, and the suite's 52 entries and M0 are green.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>