[startup] auto-select GPU backend

start.py

@@ -47,17 +47,32 @@ def get_install_features(lib_name: str = None):
     possible_features = ["cu12", "amd"]
 
     if not lib_name:
-        # Ask the user for the GPU lib
-        gpu_lib_choices = {
-            "A": {"pretty": "NVIDIA Cuda 12.x", "internal": "cu12"},
-            "B": {"pretty": "AMD", "internal": "amd"},
-        }
-        user_input = get_user_choice(
-            "Select your GPU. If you don't know, select Cuda 12.x (A)",
-            gpu_lib_choices,
-        )
-
-        lib_name = gpu_lib_choices.get(user_input, {}).get("internal")
+        has_nvidia = which("nvidia-smi") is not None
+        has_rocm = which("rocm-smi") is not None
+        has_amd = which("amd-smi") is not None
+        has_amd_gpu = has_rocm or has_amd
+
+        if has_nvidia and not has_amd_gpu:
+            lib_name = "cu12"
+            print("Auto-detected NVIDIA GPU. Using CUDA 12.x backend.")
+        elif has_amd_gpu and not has_nvidia:
+            lib_name = "amd"
+            print("Auto-detected AMD GPU. Using AMD backend.")
+        else:
+            gpu_lib_choices = {
+                "A": {"pretty": "NVIDIA Cuda 12.x", "internal": "cu12"},
+                "B": {"pretty": "AMD", "internal": "amd"},
+            }
+            print(
+                "WARNING: Auto-detection failed. "
+                "Please ensure you have either an NVIDIA GPU (with nvidia-smi) "
+                "or an AMD GPU (with rocm-smi or amd-smi) installed."
+            )
+            user_input = get_user_choice(
+                "Select your GPU. If you don't know, select Cuda 12.x (A)",
+                gpu_lib_choices,
+            )
+            lib_name = gpu_lib_choices.get(user_input, {}).get("internal")
 
         # Write to start options
         start_options["gpu_lib"] = lib_name