#24574 cmux NEXT session rail grows with content

Leo said:

“lawrence sees a cut off thing... but more importantly, this session side machine/project info can prob maybe be off by default maybe?”

“also we shouldnt be cutting our stuff off like that idk why there's seemingly some hard set max height but that's not the point of the session rail??? if you look at the attached chatgpt thing they just let it hang to the bottom if it needs it... or you should just be able to do a show more or view all type thing tho that one im not sure of. maybe scroll is ok, but just constrain some of the individual side things, not the entire bar until it's the window size itself's height.”

Before: the Session Info rail stopped at a fixed 560px ceiling and nested long-list scroll boxes, while machine and folder rows were always present. After: the rail grows to the window bottom and owns scrolling; Outputs, Subagents, and Background tasks show about six rows with a View all row; machine and folder rows are hidden by default and controlled by the new Agent Chat setting.

The gallery has three long-list treatments (rail-view-all, rail-scroll, rail-all); rail-view-all is shipped. It also includes hidden and enabled environment states.

Validation:

• Focused Inspector tests: 38 passed across Outputs, Environment, Tasks, Subagents, Chat Inspector, and Chat Display.
• python3 scripts/cmux-next/prepush-gate.py: passed.
• bun run check: reached the existing base TypeScript errors in test/new-tab-composer-layout.test.tsx and test/thread-minimap-stream.test.tsx; no changed-file lint errors.
• bunx vp lint <changed files> and bunx vp fmt --check: passed.
• Open PR overlap snapshot found related Inspector PRs #23990 and #24463, but no duplicate for this rail growth and environment visibility slice.

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Summary by cubic

Fixes the Session Info rail so it grows with its content instead of stopping at a fixed 560px height with nested scroll boxes.

• The rail now extends to the window bottom and its body scrolls when content is taller than the pane.
• Outputs, Subagents, and Background tasks each show about six rows followed by a View all row, replacing per-section scroll lists.
• Machine and folder rows are hidden by default; the new Show Machine and Folder setting under Agent Chat reveals them.