The solver's position key reads stackAt (each tile oldest first). New tool
tools/verify-levels.mjs checks course/10-spellgrid/levels/proofs.json: each
level's shortest solution, and that it exhausts without its idea (neverRule)
or on the naive engine. Levels 4-10, one course idea each, with
test_10_level_N_solution in both tracks, scenarios and Lesson 10's list;
l1 no longer matches l10, and proofs.json is not listed as a level.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
