RenderSubmesh carries stage 1 (texture, UV set, transform, Mod/Mod2x) for
textureCount 2 batches; M2Vertex reads UV1. WowModelExt gains a stage1
uniform + texture binding 94/95 and the WOW_STAGE1 shader def, so every
one-texture batch compiles the old code. The skybox lane binds stage 1 on
its own material copies and drives its transform rows.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
