Take a published assistant, or one of its copies, down.

What comes down depends on which id is given, so the caller can be as broad or as narrow as they need:

• the assistant's id — everything: the live copy and any submission still under review;
• a posted copy's id — only the live one, leaving a pending submission queued;
• a pending copy's id — only the submission, withdrawing it while the live version stays up.

The slug stays on the assistant either way, so publishing again reuses the same public URL.