Expanding now takes the conversation's place rather than the window's: covering everything left the rail underneath with its toggle still on screen and doing nothing visible. Collapse the rail too and the document fills the window. Back is gone and expand takes the left slot, as one button with Maximize2 / Minimize2. The header matches the conversation header's metrics so the two line up across the seam, the documents button hides while the pane is open, and expand hides on the list, where it would mean nothing. AGENTS.md gains the [hidden] gotcha — an author display outranks the attribute's UA display:none, and it always presents as a JS bug. Three instances this week.