turn.undo.test.js: every op with log.undo roundtrips to prior state.
startEncounter, nextTurn, togglePause, applyHpChange, toggleCondition,
toggleParticipantActive, addParticipant, removeParticipant, endEncounter.
Found: reorderParticipants returns log:null. Cannot undo. Documents as
BUG-7 candidate (test green now, asserts current behavior).
david raistrick