Web chat: completed turns collapse into the Thinking chip and content slides under 'Earlier activity' mid-read

On the macOS desktop app, multi-step turns that finished normally still render as a collapsed 'Thinking... N steps' chip, and earlier messages get moved under an 'Earlier activity' divider while the user is still reading them. The full text exists but sits behind folds the user didn't ask for, so long answers read as missing or truncated. Screenshots confirm the final message appears both expanded and duplicated under 'Earlier activity'. Request: completed turns stay expanded by default (or a setting to disable folding), and the 'Earlier activity' boundary shouldn't advance while the user is actively viewing that content.