Better captions for voice demos

Voice demos show captions so you can read along with the conversation. Subtitles have been around since silent film, so we assumed this part would be easy. It was not. Live captions for a two-way conversation involve more edge cases than we would like to discuss: the agent talks, listens, and drives a real browser at the same time, and you're allowed to interrupt it mid-sentence. We've reworked how the captions follow all of this.

• Captions follow the voice. What's on screen is what's being said, word by word.
• Pausing to think is allowed. Your caption stays up while you find the rest of your sentence.
• Interruptions work. Cut the agent off and your words take over.
• The dots mean it's still working. They show while your answer is on the way, including while the agent is off clicking around the product.