Fix: Robust HF cache directory with graceful /data fallback

- Handle PermissionError when /data is not accessible
- Auto-fallback: /data/.huggingface → /home/user/.cache
- Add write permission verification
- Support both paid tier and free tier

Resolves: PermissionError [Errno 13] Permission denied: '/data'

code/cube3d/config.py

@@ -58,22 +58,54 @@ DATA_DIR = PROJECT_ROOT / "data"
 CAR_1K_DIR = DATA_DIR / "car_1k"
 CAR_DATA_DIR = DATA_DIR / "1313个筛选车结构和对照渲染图"
 
-# HuggingFace model cache directory
-# Use /data for persistent storage (writable in HF Spaces)
+# HuggingFace model cache directory with robust fallback handling
+# Priority: /data/.huggingface (persistent storage) → /home/user/.cache/huggingface (backup)
 if ENVIRONMENT == "huggingface":
-    # /data is persistent and writable in HF Spaces
-    HF_CACHE_DIR = os.getenv("HF_HOME", "/data/.huggingface")
-    print(f"[Config] Using HF cache directory: {HF_CACHE_DIR}")
+    # HuggingFace Spaces: Try persistent storage with graceful fallback
+
+    # Candidate directories in priority order
+    candidates = [
+        os.getenv("HF_HOME", "/data/.huggingface"),  # Persistent storage (paid tier)
+        "/home/user/.cache/huggingface",              # Ephemeral but always writable
+    ]
+
+    HF_CACHE_DIR = None
+    for cache_dir in candidates:
+        try:
+            # Attempt to create directory to verify write permissions
+            os.makedirs(cache_dir, exist_ok=True)
+
+            # Test write access by creating a test file
+            test_file = os.path.join(cache_dir, ".write_test")
+            with open(test_file, 'w') as f:
+                f.write("test")
+            os.remove(test_file)
+
+            # Success! Use this directory
+            HF_CACHE_DIR = cache_dir
+            print(f"✅ [Config] HuggingFace cache directory: {HF_CACHE_DIR}")
+            break
+
+        except (PermissionError, OSError) as e:
+            print(f"⚠️  [Config] Cannot use {cache_dir}: {e}")
+            continue
+
+    # Fallback if all candidates failed (should never happen)
+    if HF_CACHE_DIR is None:
+        HF_CACHE_DIR = tempfile.gettempdir()
+        print(f"⚠️  [Config] Using system temp directory as last resort: {HF_CACHE_DIR}")
 
-    # Ensure directory exists
-    os.makedirs(HF_CACHE_DIR, exist_ok=True)
 else:
-    # Local development
+    # Local development: use standard user cache
     HF_CACHE_DIR = os.path.expanduser("~/.cache/huggingface")
-
-# Ensure cache directory exists (fallback for local)
-if ENVIRONMENT != "huggingface":
-    os.makedirs(HF_CACHE_DIR, exist_ok=True)
+    try:
+        os.makedirs(HF_CACHE_DIR, exist_ok=True)
+        print(f"[Config] Local HuggingFace cache directory: {HF_CACHE_DIR}")
+    except (PermissionError, OSError) as e:
+        # Fallback to temp directory
+        HF_CACHE_DIR = os.path.join(tempfile.gettempdir(), "huggingface")
+        os.makedirs(HF_CACHE_DIR, exist_ok=True)
+        print(f"⚠️  [Config] Using temp directory due to permission error: {HF_CACHE_DIR}")
 
 
 # ============================================================================