HTML-panel interaction probe — GPU pick → offscreen DOM
The DOM panel lives in the canvas layoutsubtree at a fixed position with pointer-events:none — it is never moved and never directly clickable. The only path to it is the MRT GPU picker: it resolves the panel + world hit point (depth-tested, so the cube genuinely occludes), and the real pointerdown synchronously actuates the resolved sub-element with a programmatic method — click() / focus() / showPicker() / Selection API / clipboard. No slide.
empirical probe: how do the HTMLTexture + pick pipelines fare off WebGPU? Shared choice (all DOM-in-3D test routes), persisted; toggling reloads — a canvas can't swap context kinds in place.
Booting WebGPU + picker…