Function inject_truncations 

pub fn inject_truncations(src: &str, table: &SymbolTable) -> String

Walk var X: TYPE = <expr>; (or let) declarations and fix HLSL- implicit-conversion mismatches between LHS type and RHS type:

• f32 = vec: rewrite RHS to (<expr>).x (HLSL truncation).
• vec = scalar: rewrite RHS to vecN<f32>(<expr>) (HLSL broadcast).

The pass is intentionally conservative: only fires when the LHS type is known and the inferred RHS type is the other of the two cases above. Anything ambiguous (Unknown RHS) passes through.

Why this exists: MD2 user shaders frequently write float3 bg = pow(length(dz), 0.7)*2 + GetBlur1(uv).y*2; — RHS is scalar, LHS is vec3; HLSL silently broadcasts, WGSL rejects with the type of bg is expected to be vec3<f32> but got f32. Mirror case: float lum = GetPixel(uv) * c.x; — RHS vec3, LHS f32.