Shared MySQL drill engine extracted from testsAndMisc: sandboxed
per-run db and user, exact-match cell diff, predict drills (builtin
theory set incl. an error drill), save_generated validation.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WzxdWYGW5NZL5uVpnqmNKo