Fix nvdiffrast ABI mismatch + pymeshfix TrackedArray crash

- Replace Jeff Xiang's prebuilt nvdiffrast wheel (built against PyTorch
~2.5.x) with a source build from git so it compiles against torch 2.8.0
- Add packages.txt with ninja-build and OpenGL headers needed for compilation
- Fix pymeshfix load_array crash: cast trimesh TrackedArray to plain
np.ndarray with correct dtypes (float64 vertices, int32 faces)

packages.txt

@@ -0,0 +1,6 @@
+# System packages installed by HF Spaces before pip install runs.
+# Required to build nvdiffrast from source against torch 2.8.0.
+ninja-build
+libgl1-mesa-glx
+libgles2-mesa-dev
+libglfw3-dev

requirements.txt

@@ -50,10 +50,11 @@ xatlas
 scipy               # normal map dilation
 
 # ===== Milestone 5: Stage 2F Normal Baking =====
-# nvdiffrast is not on PyPI — use Jeff Xiang's prebuilt wheel.
-# If this fails ABI checks at import time the baking functions
-# degrade gracefully (they catch ImportError internally).
-https://github.com/JeffreyXiang/Storages/releases/download/Space_Wheels_251210/nvdiffrast-0.4.0-cp310-cp310-linux_x86_64.whl
+# Build nvdiffrast from source against the installed torch version.
+# Jeff Xiang's prebuilt wheel (Space_Wheels_251210) was compiled against
+# PyTorch ~2.5.x and fails with an ABI mismatch on torch 2.8.0.
+# Source build via git requires ninja-build + OpenGL headers (packages.txt).
+git+https://github.com/NVlabs/nvdiffrast.git
 
 coacd==1.0.4  # Milestone 8 collision
 

src/stages/stage2_repair.py

@@ -3,6 +3,8 @@ from __future__ import annotations
 
 from pathlib import Path
 
+import numpy as np
+
 from src import workspace
 from src.workspace import CURRENT
 
@@ -13,7 +15,10 @@ def repair_mesh(input_glb: Path) -> tuple[Path, str]:
     import pymeshfix
 
     mesh = trimesh.load(str(input_glb), force="mesh")
-    v, f = mesh.vertices.copy(), mesh.faces.copy()
+    # pymeshfix.load_array requires plain ndarray (not TrackedArray subclass),
+    # float64 vertices, int32 faces, C-contiguous.
+    v = np.ascontiguousarray(mesh.vertices, dtype=np.float64)
+    f = np.ascontiguousarray(mesh.faces, dtype=np.int32)
 
     tin = pymeshfix.PyTMesh()   # verbose kwarg removed in pymeshfix ≥ 0.17
     tin.load_array(v, f)