Diff file tree doesn't jump to a file, and added lines are hard to read #620

In the Diff tab, clicking a file in the tree doesn't move to its patch, and added lines are hard to read.

What was seen

• Show file tree → click todo.md (out of view): the file is highlighted in the tree, and a search is cleared, but "the diff's scroll position stayed at 0 after two clicks". The map expects "Clicking a file scrolls to its patch" (^687).
• Added lines ("hello from ace", "tabs test", and the bulk files' "File 1", "File 10") are "pale text on a pale green background", "nearly invisible" (^692).
• The dot.png Binary and bulk 120 files rows look clickable but do nothing: no preview, no way to list the 120 files (^688).
• Each file header shows only the bare name, so files in different folders can't be told apart without the tree (^684).

Steps

1. Ask the agent to change README.md, add notes/todo.md, a PNG and a folder of 120 files.
2. Open the Diff tab, shrink the window so todo.md is off screen, Show file tree → click todo.md.

Rig: web (loopback source host from origin/main, 0.0.53 code).

Map: ^687, ^692, ^688, ^684.

Found in the 2026-10-22 map study.