keys.delete returned the number of selected keys even when some of them
no longer existed, so a delete that removed nothing still reported success.
It now returns the number of keys actually removed, and a key that is gone
or listed twice is not counted.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JaA7tHy731qtvscjulrcfz
