The toolkit: nodes, modifiers, layout, widgets, input. No engine, no OpenGL, no AWT.

The effects the toolkit ships: blur, outline, colour grade, dissolve. Public API only.

The in-play widgets: bars, reticle, hotbar, cooldowns, minimap, damage numbers, particles. Public API only.

The Android half of a backend: the parts of a phone no engine reports.

Debug tooling for development builds: the inspector, the developer console, and the layout, focus, redraw, overdraw, text and frame budget overlays. Public API only.

The one renderer every backend draws with: canvas, batch, layers, glyph atlas and the OpenGL device.

Shared test material: the scenes every backend must draw the same, and golden comparison.