[FEATURE] Desktop app: make it obvious how to collapse an expanded thinking block (and hold scroll position)

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Thanks for the desktop app. The streaming thinking summary is one of my favorite things about working in it -- being able to peek at the reasoning mid-run is how I catch a wrong turn early, so I click into it often.

Clicking the "...almost done thinking" label expands the thinking block. Once it is open I get a long continuous block of text, and I cannot find any control to put it back. Because the block is tall, everything above it is pushed far up: my own prompt for that turn ends up several screens off the top, and getting back to it means a lot of scrolling. Over a session with a few expanded blocks, this compounds.

If re-clicking the original label already collapses it, that is not discoverable -- by the time the block is open, the label has scrolled off-screen, and nothing on the expanded block indicates it is clickable.

Proposed Solution

1. A discoverable collapse control on an expanded thinking block -- a chevron or a "hide thinking" affordance at the top of the block, ideally sticky so it stays reachable without scrolling back up through the block.
2. Preserve scroll anchoring across collapse/expand, so the message being read stays where it is instead of the viewport jumping.
3. Optional: a preference to keep thinking collapsed by default.

Alternative Solutions

Today the workaround is manual scrolling back up to find my prompt, which is what makes long sessions hard to navigate. A keyboard shortcut to jump to the last user message would help but would not address the root issue (an expanded block with no visible way out).

#73789 asks for a compact/collapsed-by-default mode, but it is scoped to the VS Code extension and is about the default state rather than getting back out of an already-expanded block.

Priority

Medium - Would be very helpful

Feature Category

Other

Use Case Example

Long multi-step session in the desktop app. I expand the thinking on one turn to check the reasoning, read it, and then want to get back to my own prompt to compare it against what I asked for. Right now that means scrolling past the whole expanded block with no way to fold it away first.

Additional Context

Environment: Claude Code desktop app 1.24012.9, macOS (Darwin 25.5.0), claude-code 2.1.219.