wip(assembler): M2 round 2 -- same-LOD borders watertight for MC/hybrid/DC; LOD0/1 transitions still open

Shared halo + deterministic border-quad ownership + T-junction conformance: 625/625 same-LOD for all three.
LOD 2:1 prototype (collar zipper) fails MC 5 / hybrid 38 / DC 40 cases (corners, overhangs).
Hybrid is bit-identical to MC on a sampled native SurfaceWorld cliff; DC rougher. Standalone only.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MmSoF64BbRFmk9C3p1VsBJ

Standalone/Research/WorldAssemblerM2/RenderSharpMesherCaptures.py

@@ -19,6 +19,7 @@ PIECES = (
     ("riser1m", "one metre riser"),
     ("cliff_overhang", "cliff ledge / overhang"),
     ("organic_cave_chamber", "organic cave chamber wall"),
+    ("native_surface_cliff", "sampled SurfaceWorld cliff"),
 )
 WIDTH, HEIGHT = 288, 216
 BG = (239, 242, 244)
@@ -56,14 +57,26 @@ def read_obj(path: Path):
     return vertices, normals, faces
 
 
-def project_mesh(vertices, faces, seam=False):
+def project_mesh(vertices, faces, seam=False, target=None):
     # One view is reused for every candidate in a row: azimuth 38°, elevation 27°.
-    target = (0.0, 0.0, 0.0)
+    if target is None:
+        if vertices:
+            bounds_min = tuple(min(v[i] for v in vertices) for i in range(3))
+            bounds_max = tuple(max(v[i] for v in vertices) for i in range(3))
+            target = tuple((bounds_min[i] + bounds_max[i]) * 0.5 for i in range(3))
+        else:
+            target = (0.0, 0.0, 0.0)
     view_dir = normalize((8.0, -10.0, 7.0))
     forward = tuple(-c for c in view_dir)
     right = normalize(cross(forward, (0.0, 0.0, 1.0)))
     up = normalize(cross(right, forward))
-    scale = 20.2
+    projected_bounds = []
+    for point in vertices:
+        rel = tuple(point[i] - target[i] for i in range(3))
+        projected_bounds.append((dot(rel, right), dot(rel, up)))
+    span_x = max((point[0] for point in projected_bounds), default=0.0) - min((point[0] for point in projected_bounds), default=0.0)
+    span_y = max((point[1] for point in projected_bounds), default=0.0) - min((point[1] for point in projected_bounds), default=0.0)
+    scale = min(20.2, 0.84 * min((WIDTH - 24) / max(span_x, 1.0e-6), (HEIGHT - 24) / max(span_y, 1.0e-6)))
     projected = []
     for p in vertices:
         rel = tuple(p[i] - target[i] for i in range(3))
@@ -102,7 +115,10 @@ def raster(path: Path, color_by_x=False):
             for i in range(1, len(clipped) - 1):
                 clipped_faces.append(((first, first), (first + i, first + i), (first + i + 1, first + i + 1)))
         vertices, normals, faces = clipped_vertices, clipped_normals, clipped_faces
-    projected = project_mesh(vertices, faces, color_by_x)
+    bounds_min = tuple(min(v[i] for v in vertices) for i in range(3))
+    bounds_max = tuple(max(v[i] for v in vertices) for i in range(3))
+    target = tuple((bounds_min[i] + bounds_max[i]) * 0.5 for i in range(3))
+    projected = project_mesh(vertices, faces, color_by_x, target)
     pixels = Image.new("RGB", (WIDTH, HEIGHT), BG)
     zbuf = [float("inf")] * (WIDTH * HEIGHT)
     px = pixels.load()
@@ -146,7 +162,7 @@ def raster(path: Path, color_by_x=False):
         draw = ImageDraw.Draw(pixels)
         # Project a visible segment on the LOD boundary plane, x=0.
         seam_world = [(-0.0, y, z) for y, z in ((-4, -4), (4, -4), (4, 4), (-4, 4), (-4, -4))]
-        seam_points = project_mesh(seam_world, [], True)
+        seam_points = project_mesh(seam_world, [], True, target)
         draw.line([(p[0], p[1]) for p in seam_points], fill=(181, 55, 49), width=2)
     return pixels
 
@@ -174,14 +190,14 @@ def main():
         captures.append(row)
     seam_row = []
     for method in METHODS:
-        obj = RESULTS / "meshes" / f"lodseam_cliff_overhang_{method}.obj"
-        image = capture_title(raster(obj, color_by_x=True), "LOD0 to LOD1 cliff seam", f"{method} | fine left, coarse right, x=0 seam")
-        path = CAPTURES / f"lodseam_{method}.jpg"
+        obj = RESULTS / "meshes" / f"lodseam_cliff_crossing_{method}.obj"
+        image = capture_title(raster(obj, color_by_x=True), "Sharp cliff across LOD border", f"{method} | LOD0 left, LOD1 right, x=0")
+        path = CAPTURES / f"lodseam_cliff_crossing_{method}.jpg"
         image.save(path, quality=86, optimize=True)
         seam_row.append(image)
     captures.append(seam_row)
 
-    sheet = Image.new("RGB", (WIDTH * 3, (HEIGHT + 30) * 6), (221, 227, 230))
+    sheet = Image.new("RGB", (WIDTH * 3, (HEIGHT + 30) * len(captures)), (221, 227, 230))
     draw = ImageDraw.Draw(sheet)
     for row_index, row in enumerate(captures):
         for col_index, image in enumerate(row):