The Mermaid and HTML previews are the kind of quality-of-life additions that feel obvious in retrospect — both required third-party extensions before 1.121. Mermaid diagrams now render inline in Markdown and notebook contexts with pan/zoom support for larger graphs. HTML files get a right-click "Open in Integrated Browser" path that skips the Live Server detour. The Remote Agent Sessions feature is the one to watch. It uses a new open Agent Host Protocol (AHP) and treats the remote agent host as long-lived — sessions survive client disconnects. That's a meaningful shift: agents can now run on dedicated machines rather than being tethered to a developer's local environment. Still in preview, but the architecture is laid out.