_is_uuid took an uppercase or mixed-case uuid, and the paths built from it
are the live lowercase session's own files on macOS's default
case-insensitive APFS. The in-use checks compare exactly, though: session
files and command lines carry the lowercase id, so `purge claude <UPPER>`
found no holder and could remove a live session's files. _canonical now
lowercases a canonical uuid, and the paths, the session-file and job
matches, the in-use check and the residual all use it; a command line is
searched for both spellings.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>