onAsanaTaskCompleted specializes completion changes. Automate.ax fetches the task once and only emits when its current completed value is true.
automations/respond-to-asana-completion.automation.ts
resourceId is required. Optional static account defaults to the project binding.
Returns a task-changed event signal whose change.field is "completed" and change.action is "changed". It remains a compact event; call getTask for the full task. Reopening a task does not emit this trigger.