parse_rehearsal_date() extracts YYMMDD / YYYYMMDD from the file path and get_or_create() a RehearsalSession. Both the watcher nc-upload endpoint and the nc-scan endpoint now set song.session_id when a dated folder is detected. Existing songs without a session_id are back-filled on the next import of the same folder. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>