Nothing to try yet
Plumbing exists for a prefix-lock-rejection warning message, but it always renders as empty text.
Plumbing for a prefix-lock-rejection warning message is in place, including parsing of the anthropic-thinking-prefix-mismatch response header and detection of related safeguards-related 400s, but the function that generates the actual warning text currently always returns an empty string, so no message content is shown yet.