trello.onChecklistItemCompleted matches an updateCheckItemStateOnCard action whose item state is "complete".
automations/watch-trello-checklist-completions.automation.ts
board as an ID, short link, or URL. Optional static account defaults to the project binding.
Returns a resource event with actionType: "updateCheckItemStateOnCard", required checkItem.state: "complete" and board, plus actionId, occurredAt, optional checklist, card, memberCreator, and the complete provider event. The action also matches trello.onChecklistItemUpdated.