The document 'drop' listener called event.preventDefault() and stopPropagation() unconditionally on every drop. ComfyUI's native drag&drop handler bails when event.defaultPrevented is already true, so dropping any workflow file (PNG/JSON/webp) onto the canvas silently did nothing as long as Mixlab was installed. Scope preventDefault()/stopPropagation() to the application/json case actually handled here, so all other drops fall through to ComfyUI. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>