Function bake_source_at_world 

pub fn bake_source_at_world(
    source: &Mesh,
    world_row_major: &[f64; 16],
    rtc: [f64; 3],
) -> (Vec<f32>, Vec<f32>, Vec<u32>)

Bake a SOURCE-coords Mesh at a PRE-RTC row-major world transform into absolute POST-RTC world geometry (positions, normals, indices) — the #1623 Phase 2 finalize fallback for a don’t-bake instance whose template occurrence never materialized (an orphan; effectively unreachable for the eligible single-solid type-instanced set, but kept so geometry is NEVER silently lost). The affine part transforms positions; the inverse-transpose of the linear part transforms normals (renormalized). Geometrically equal to the baked flat occurrence (same triangles); the registry source is pre-weld, so vertices are unwelded — that changes only the vertex count, not the rendered surface.