Components
Resizable
Splitter panels and resize handles: an invisible 12 / 8 / 3px gap whose 3×48 pill appears 200ms after hover, turns accent and full-length on keyboard focus; tile handles for code panes; a standalone px handle (sidebar edge).
Pill handle
Hover the gap: the pill fades in after 200ms (200ms fade). Tab to the handle: accent pill, full height, no delay, plus the focus shadow on the 12px hit layer. Arrow keys resize (2 % steps), Home / End jump.
Click to collapse and tiles
The artifact panel handle (v2: 12px, “Resize file viewer”) collapses its panel on a click without drag; a drag still resizes. Tile handles (code panes) show a 3×56 20 % pill in 120ms and the primary ink while dragging.
Standalone ResizeHandle
For px widths that are not splitter panels (sidebar edge, file tree). role=separator with aria-valuenow / min / max; drag with pointer capture, ArrowLeft / Right ∓ 8px (Shift ×4), Home / End, double-click resets, a click emits toggle.