Unwrap a mesh with a vertex shader

Hello, I'm trying to unwrap a mesh according to its UV coordinates from a vertex shader and display it in screen space. I can't quite figure out why what I'm doing isn't working out. I apply it to a sphere and i just see nothing in the viewport. On occasion it will simply crash Unity. Any ideas?

 Shader "Custom/UnwrapShader" {
 Properties {
 }
 SubShader {
     Pass {
         CGPROGRAM

         #pragma vertex vert_main
         #pragma fragment frag_main
         #include "UnityCG.cginc"
     
         struct Output_Struct {
             float4 position : POSITION;
             float2 texcoord : TEXCOORD0;
         };    
         
         struct Vertex_Struct {
             float4 vertex : POSITION;
             float2 texcoord : TEXCOORD0;
         };
 
         Output_Struct vert_main (Vertex_Struct v) {
             Output_Struct OUT;

             OUT.position.xy = v.texcoord.xy * 2.0 - 1;
             OUT.position.z = 0.0;
             OUT.position.w = 1.0;
             
             return OUT;
         }
         
         float4 frag_main (Output_Struct OUT) : COLOR {
             return float4(1,1,0,1);
         }
 
         ENDCG
     }
 }
 FallBack "Diffuse"

}