Drop outer Border wrapper in WorktreesOverviewModalView so Avalonia edge resize handles reach the window frame. Add split pane to WorktreeModalView with file tree on left and per-file unified diff on right; wire SelectedNode via SelectedItem TwoWay binding + SelectionChanged fallback; add GetFileDiffAsync to GitService. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>