Root cause: dba_write_api.php's $paths registry keyed systems by OLD sequential single-digit codes (sys-01=Master...sys-10=Travel) while db-admin.html's DB_CONFIG (frontend, already correct) keys every system by its real decade code (sys-10,sys-20...sys-95). Only sys-00 (Admin) coincidentally overlapped, so every other system's Pick/edit action in db-admin.html silently 404'd with db not found. Fix: rekeyed all 10 non-Admin entries in $paths to decade codes matching DB_CONFIG exactly, no other logic touched (additive rename only, same structure). Files touched: backend/tools/critical/dba_write_api.php (backed up first to backups/20-builder/php/Builder_dba_write_api_CURRENT.php). Normally Server[40] lane (PHP/API) per D231 -- done directly on USR369's explicit go-ahead since Server was occupied elsewhere this session.