The region around the pond center is uniform dirt color (0.42, 0.37, 0.30) — that's exactly the PathMat color. The dirt path boxes are covering the pond area! The path goes from the door toward the shore and ends around (4.2,-4.2), but the boxes are long and rotated — let me check if the path crosses over the pond.

The path curve: x from -4 to 4.2, y from 1.2 to -4.2. The pond starts at (1.6,-7)... The path end (4.2,-4.2) — the pond edge at that latitude is around (1.6,-7) to (14.4,-7). Actually the pond's north edge is at y≈-0.6, so the path ending at y=-4.2 is INSIDE the pond region! The path goes into the pond.

That's the problem — the dirt path runs into the water. I need to shorten the path so it ends at the shore, before the water starts. The pond north edge at x≈4.6 is at y≈-2.5 (edge of the circle at distance 6.4 from (8,-7)). Let me recompute: the pond is a circle radius 6.4 centered (8,-7). At x=4.6, the circle edge is at y = -7 ± sqrt(6.4² - (4.6-8)²) = -7 ± sqrt(40.96-11.56) = -7 ± 5.42. So the north edge at x=4.6 is y=-1.58. The path should end before y=-1.58 at x=4.6.

Let me fix the path to end at the shore.

import bpy, math
from mathutils import Vector

mc = bpy.context.scene.collection

# remove old path boxes
for o in list(mc.objects):
    if o.name.startswith('Path'):
        mc.objects.unlink(o)
        bpy.data.objects.remove(o, do_unlink=True)

def box(name, size, loc, matname=None, rot=None):
    bpy.ops.mesh.primitive_cube_add(size=1, location=loc)
    o = bpy.context.active_object
    o.name = name
    o.scale = size
    if rot: o.rotation_euler = rot
    if matname:
        o.data.materials.clear()
        o.data.materials.append(bpy.data.materials.get(matname))
    return o

def th(x, y):
    import math as m
    h = 0.35 + 0.14*m.sin(x*0.45+1.1)*m.sin(y*0.4-0.6) \
        + 0.08*m.sin(x*1.1+3.0)*m.cos(y*0.9+1.5) \
        + 0.05*m.sin(x*2.3+0.4)*m.sin(y*2.1+0.9)
    dc = m.hypot(x+4, y-1)
    if dc < 7.0:
        t = dc/7.0; s = t*t*(3-2*t)
        h = h*s + 0.55*(1-s)
    dp = m.hypot(x-8, y+7)
    R = 6.4
    if dp < R:
        t = dp/R
        h -= 1.5*(1-t*t)*(1-t*t)
    return h

# Path from door to pond shore (north edge). Shore point: (4.3,-2.2)
seg_pts = []
for i in range(8):
    t = i/7.0
    x = -4.0 + 4.2*t + 2.6*t*t
    y = 1.2 - 3.4*t
    z = th(x, y)
    seg_pts.append((x, y, z))
for i, (x, y, z) in enumerate(seg_pts[:-1]):
    x2, y2, z2 = seg_pts[i+1]
    mx, my, mz = (x+x2)/2, (y+y2)/2, (z+z2)/2
    dx, dy = x2-x, y2-y
    ln = math.hypot(dx, dy)
    ang = math.atan2(dy, dx)
    box(f'Path{i}', (0.8, ln/2, 0.03), (mx, my, mz+0.02), 'PathMat', rot=(0, 0, ang))

print('path fixed, objects:', len(mc.objects))
print('path end', seg_pts[-1])