addParticipants + updateParticipant returned log:null → invisible in
combat log. Contract test caught them. Now both return
log:{ message, undo:{ participants }}.
App.js handlers wired (handleAddAllCharacters, handleUpdateParticipant,
handleInlineInitiative) — call logAction on logged mutations.
Logging contract now complete: every mutating combat op produces a log
entry. No gaps. turn.logging.test.js proves it.
238 tests green.