MessageResponse is the assistant-message content renderer from
smithers-orchestrator/ui. It uses the dependency-free Markdown primitive,
keeps incomplete fences and inline markers stable between stream chunks, and
adds an aria-hidden caret while streaming is true.
onLinkClick receives only sanitized scheme-less, http, https, or
mailto hrefs after default navigation has been prevented. Other schemes are
never passed to the callback. The caret stops blinking under reduced-motion
preferences.