Unreal materials (master materials, Substrate, textures, shader cost)

Expert level means a few master materials whose instances cover the kit, a known and budgeted permutation count, cost proven in milliseconds on a fixed camera, and physically plausible values before any artistic push. The graph is authored once (scripted build or template); everything else is instances, Custom Primitive Data and textures that follow a role policy. Never trust the instruction count or a pretty preview. If a sibling skill named here is missing from your available skills, ask the user to install it (npx skills add scenario-labs/skills --skill <name>); unattended, proceed from tool schemas and flag the gap.

REQUIRED BACKGROUND: scenario-unreal-expert (channels, review loop, 5.8 traps).

Status (2026-09-24): Unreal is not installed; offline tests pass (tests/code/unreal-materials/run_all.sh, editor layer on a fake unreal). Every snippet is not yet run in Unreal: run P0 first.

Stance (the expert delta)