Baba.undo() restores the level before the last step or move (board snapshot:
objects in age order with ids, the id counter, and won; rules recompiled).
place clears the history. SpellGrid's undo throws/panics 'not supported'.
stackAt / stack_at lists a tile's kinds oldest first, on Baba and SpellGrid.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Mutation runs on the references showed six surviving mutants: a live aura
scan, two turn-phase reorderings, a dropped final parse, and two hazard
reorderings. Each now fails a named test.
Co-Authored-By: Claude Fable 5.2 <noreply@anthropic.com>
Movement planned in full, then committed: a Planner builds a plan
(moving and destroyed ids) by running content's movement responses
(OPEN/SHUT, PUSH, STOP) for every step, rolling back failed branches.
Edge of level blocks; YOU objects move furthest-ahead first; rules are
reparsed once after movement. Harness: move/move_dir(Dir), posOf,
kindsAt. Expansion Drop: PULL as one word plus one content response.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
