Function infer_bool_shape 

fn infer_bool_shape(e: &Expr, ctx: &mut WalkCtx<'_>) -> WgslType

Walks the bool-producing subtree and returns the inferred vector shape of the underlying values being compared. Returns F32 for scalar bool (so the caller emits scalar literals), VecN for vector bool, Unknown when nothing can be inferred (caller falls back to scalar — which matches the conservative pre-AA behaviour).