Example of how to copy geometry with a VEX node in Houdini.

copyGeo.h

int numVerts = nvertices(1);
int numPoints = npoints(1);
int numPrim = nprimitives(1);

int ptTally = 0;

// copy all the primitives,vertex data, and indices.
for(int p = 0; p < numPrim; ++p){
    int prim = addprim(0,"poly");
    
      // get vertices for primitive 
    int primverts[] = primvertices(1,p);
   
    for(int a = 0; a < len(primverts);++a){
        int pt = vertexpoint(1,primverts[a]);
        addpoint(0,pt);
        addvertex(0,prim,pt);
        
        ptTally += 1;
    }
}

// the last process will create a glut of points that we need to trim.
// we will also need to give those points value. 
for(int i = ptTally; i > numPoints - 1; --i){
    removepoint(0,i);
}

// re-value the point positions on the output 
for(int i = 0; i < npoints(1); ++i){
    vector pos = point(1,"P",i);
    setpointattrib(0,"P",i,pos);
}

I am learning Houdini and I was trying to think of how to copy a piece of geometry completely in VEX. This is probably not something done often if at all but the problem bugged me enough that I spent far too much time working on it.

This assumes your node is set to Detail for the Run Over setting and that the geometry you want to copy is wired to input 1 with input 0 being free.

Hopefully this is helpful to someone.