[Claudesaul]

Problem

Closing the right panel makes the thread details button jump about 475px across the window on the first frame, while the panel edge is still far away. Opening doesn't do this: the button rides the edge of the chat.

Change

The chat header and the window's top right each have their own copy of this button, and closing swaps one for the other. The top right one now starts where the header's sat and slides into its slot, on the panel's own timing, so it travels with the closing edge.

Scope and approval

Small fix for an obvious jump. What the button does hasn't changed.

Verification

• To reproduce: set panel animations to 300ms, open the right panel and close it.
• Chromium on macOS at 1280×800 against the dev server: I froze the close at set points and measured the button. On main it's at 1175px from the first frame. Here it starts at 700px, where the header's button sat, stays just inside the closing edge, and lands at 1175px.
• Closing a maximized panel or closing with animations off doesn't slide the button, and reopening partway through a close leaves it in the right place.
• vp test run apps/web/src/components/chat (598 passed); web typecheck and lint clean.
• Not checked: the Electron window. Its Windows and Linux title bars space these buttons differently.

Recording: a few opens and closes at regular speed, then one close and open zoomed in at quarter speed. Both sides include the panel fix from pingdotgg#28922, so only this change differs.

Before	After

Model: Claude Opus 5.5; harness: T3 Code.