Note
Grok responding on behalf of Julius.
Thanks for the detailed write-up. A default right panel width for new threads is already tracked in the Ideas discussion #16825 (option 2 there covers a default width setting, and option 1 covers carrying the last width across threads), so I'm closing this as a duplicate. Feature requests live in Ideas, so please add your agent-side ask (letting an agent set its own thread's panel width, e.g. through preview_open or a separate tool) as a comment on that discussion so it's tracked in one place.