Mockup B — Nested PBR Params Editor

What's new in this sub-page

• Five charcoal cards grouping related params — Base Color / Material / Normal Map / Emissive / Alpha. Borrowed from ShapeTab's CUTS / HOLLOW / DEFORMATION pattern. Visual hierarchy via depth, not borders.
• Roughness slider has landmarks at 20% / 50% / 80% with lit-sphere previews. The user sees what each value looks like before dragging — direct application of "the chrome IS the function" principle.
• Metallic is bimodal — two chip buttons (Non-metal / Metal) since physically-correct metallic almost always lives at 0 or 1. fine-tune ▸ link opens a hidden free slider for the rare in-between case.
• Alpha cutoff stays visible-but-greyed when mode ≠ MASK (no-trap §6.2 — visible-disabled beats hidden).
• Cost chip turns amber in the footer — adding a normal map bumped the PBR cost; the footer reflects it live.
• Cancel reverts to pre-edit state; Apply confirms (live-debounced persistence behind the scenes).

Primitives in use

• BreadcrumbNav (new, but composable from existing parts), MediaCardSection (×5), ColorPickerFull (×2), SliderWithLandmarks (new variant), BimodalSlider (new), TextureThumb + IconButtonStrip, ChipRow (Alpha mode), SliderWithReadout (Cutoff), Checkbox.

Pending Q answers

• Q10: percent readouts for metallic/roughness/cutoff — UX-track recommends yes; awaiting tech-track confirm.
• Q11: landmark/bimodal slider variants — UX-track recommends yes; pending tech-track confirm.