Minor API name issue (`smooth_vert`). Continuing with the existing terrain:

import bpy, bmesh, math

scene = bpy.context.scene
ter = bpy.data.objects["Ground"]
me = ter.data

bm = bmesh.new(); bm.from_mesh(me)
bmesh.ops.smooth_vert(bm, verts=bm.verts, factor=0.6)
bm.to_mesh(me); bm.free()

for p in me.polygons: p.use_smooth = True
me.shade_smooth()

def link_to(obj, cname):
    col = bpy.data.collections.get(cname)
    if col is None:
        col = bpy.data.collections.new(cname); scene.collection.children.link(col)
    for c in list(obj.users_collection): c.objects.unlink(obj)
    col.objects.link(obj)
link_to(ter, "Terrain")

# ---------- terrain material ----------
mat = bpy.data.materials.new("GroundMat"); mat.use_nodes = True
nt = mat.node_tree; nt.nodes.clear()
out = nt.nodes.new("ShaderNodeOutputMaterial"); out.location=(600,0)
bsdf = nt.nodes.new("ShaderNodeBsdfPrincipled")
nt.links.new(bsdf.outputs['BSDF'], out.inputs['Surface'])
attr = nt.nodes.new("ShaderNodeAttribute"); attr.attribute_name="mask"; attr.location=(-500,100)
sep = nt.nodes.new("ShaderNodeSeparateColor"); sep.location=(-320,100)
nt.links.new(attr.outputs['Color'], sep.inputs['Color'])
mix = nt.nodes.new("ShaderNodeMixRGB"); mix.blend_type='MIX'; mix.location=(-100,150)
mix.inputs['Color1'].default_value=(0.088,0.135,0.045,1)
mix.inputs['Color2'].default_value=(0.205,0.235,0.075,1)
nt.links.new(sep.outputs['Green'], mix.inputs['Fac'])
m2 = nt.nodes.new("ShaderNodeMixRGB"); m2.blend_type='MIX'; m2.location=(80,150)
m2.inputs['Color1'].default_value=(0,0,0,1)
m2.inputs['Color2'].default_value=(0.44,0.365,0.245,1)
nt.links.new(mix.outputs['Color'], m2.inputs['Color1'])
nt.links.new(sep.outputs['Blue'], m2.inputs['Fac'])
m3 = nt.nodes.new("ShaderNodeMixRGB"); m3.blend_type='MIX'; m3.location=(260,150)
m3.inputs['Color2'].default_value=(0.185,0.125,0.075,1)
nt.links.new(m2.outputs['Color'], m3.inputs['Color1'])
nt.links.new(sep.outputs['Red'], m3.inputs['Fac'])
m4 = nt.nodes.new("ShaderNodeMixRGB"); m4.blend_type='MIX'; m4.location=(420,150)
m4.inputs['Color2'].default_value=(0.075,0.072,0.055,1)
nt.links.new(m3.outputs['Color'], m4.inputs['Color1'])
nt.links.new(sep.outputs['Alpha'], m4.inputs['Fac'])
nt.links.new(m4.outputs['Color'], bsdf.inputs['Base Color'])

texco = nt.nodes.new("ShaderNodeTexCoord"); texco.location=(-500,-250)
noiz = nt.nodes.new("ShaderNodeTexNoise"); noiz.location=(-320,-250)
noiz.inputs['Scale'].default_value=0.35; noiz.inputs['Detail'].default_value=6
rampv = nt.nodes.new("ShaderNodeMapRange"); rampv.location=(-140,-250)
rampv.inputs['From Min'].default_value=0.35; rampv.inputs['From Max'].default_value=0.72
rampv.inputs['To Min'].default_value=0.72; rampv.inputs['To Max'].default_value=0.95
nt.links.new(texco.outputs['Object'], noiz.inputs['Vector'])
nt.links.new(noiz.outputs['Fac'], rampv.inputs['Value'])
nt.links.new(rampv.outputs['Result'], bsdf.inputs['Roughness'])
bumpn = nt.nodes.new("ShaderNodeTexNoise"); bumpn.location=(-320,-480)
bumpn.inputs['Scale'].default_value=2.2; bumpn.inputs['Detail'].default_value=8
bmp = nt.nodes.new("ShaderNodeBump"); bmp.location=(80,-480)
bmp.inputs['Strength'].default_value=0.22; bmp.inputs['Distance'].default_value=0.03
nt.links.new(texco.outputs['Object'], bumpn.inputs['Vector'])
nt.links.new(bumpn.outputs['Fac'], bmp.inputs['Height'])
nt.links.new(bmp.outputs['Normal'], bsdf.inputs['Normal'])
ter.data.materials.append(mat)

result = {"ok": True, "mat": mat.name}


Traceback (most recent call last):
  File "<repo>\.runner\blender-mcp-v1.0.0\addon\mcp_to_blender_server.py", line 230, in _execute_code
    exec(code, namespace)
    ~~~~^^^^^^^^^^^^^^^^^
  File "<string>", line 47, in <module>
KeyError: 'bpy_prop_collection[key]: key "Alpha" not found'