fix: gate CUDA directory checks on GPU vendor to prevent false CUDA detection

Container images that install CUDA runtime libraries (e.g., cuda-cudart-12-5
via apt) create /usr/local/cuda-12 directories as a side effect. The previous
code checked for these directories before checking whether a GPU was present,
causing CPU-only hosts to select a CUDA backend that crashes because
libcuda.so.1 is absent.

Reorder checks so CUDA directory existence only refines the capability when
an NVIDIA GPU is actually detected, consistent with the arm64 L4T code path.

Signed-off-by: Sertac Ozercan <sozercan@gmail.com>

Author: sozercan

pkg/system/capabilities.go

@@ -132,29 +132,32 @@ func (s *SystemState) getSystemCapabilities() string {
 		}
 	}
 
-	if cuda13DirExists {
-		s.systemCapabilities = nvidiaCuda13
-		return s.systemCapabilities
-	}
-
-	if cuda12DirExists {
-		s.systemCapabilities = nvidiaCuda12
-		return s.systemCapabilities
-	}
-
+	// No GPU detected → default capability
 	if s.GPUVendor == "" {
 		xlog.Info("Default capability (no GPU detected)", "env", capabilityEnv)
 		s.systemCapabilities = defaultCapability
 		return s.systemCapabilities
 	}
 
-	// If vram is less than 4GB, let's default to CPU but warn the user that they can override that via env
+	// GPU detected but insufficient VRAM → default with warning
 	if s.VRAM <= 4*1024*1024*1024 {
 		xlog.Warn("VRAM is less than 4GB, defaulting to CPU", "env", capabilityEnv)
 		s.systemCapabilities = defaultCapability
 		return s.systemCapabilities
 	}
 
+	// CUDA directories refine capability only for NVIDIA GPUs
+	if s.GPUVendor == Nvidia {
+		if cuda13DirExists {
+			s.systemCapabilities = nvidiaCuda13
+			return s.systemCapabilities
+		}
+		if cuda12DirExists {
+			s.systemCapabilities = nvidiaCuda12
+			return s.systemCapabilities
+		}
+	}
+
 	s.systemCapabilities = s.GPUVendor
 	return s.systemCapabilities
 }

pkg/system/capabilities_test.go

@@ -0,0 +1,129 @@
+package system
+
+import (
+	"os"
+	"runtime"
+
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("getSystemCapabilities", func() {
+	const eightGB = 8 * 1024 * 1024 * 1024
+	const twoGB = 2 * 1024 * 1024 * 1024
+
+	var (
+		origEnv    string
+		origCuda12 bool
+		origCuda13 bool
+	)
+
+	BeforeEach(func() {
+		if runtime.GOOS == "darwin" {
+			Skip("darwin short-circuits before reaching CUDA logic")
+		}
+
+		origEnv = os.Getenv(capabilityEnv)
+		os.Unsetenv(capabilityEnv)
+
+		origCuda12 = cuda12DirExists
+		origCuda13 = cuda13DirExists
+	})
+
+	AfterEach(func() {
+		cuda12DirExists = origCuda12
+		cuda13DirExists = origCuda13
+
+		if origEnv != "" {
+			os.Setenv(capabilityEnv, origEnv)
+		}
+	})
+
+	type testCase struct {
+		gpuVendor      string
+		vram           uint64
+		cuda12         bool
+		cuda13         bool
+		wantCapability string
+		wantTokens     []string
+	}
+
+	DescribeTable("capability detection",
+		func(tc testCase) {
+			cuda12DirExists = tc.cuda12
+			cuda13DirExists = tc.cuda13
+
+			s := &SystemState{
+				GPUVendor: tc.gpuVendor,
+				VRAM:      tc.vram,
+			}
+
+			Expect(s.getSystemCapabilities()).To(Equal(tc.wantCapability))
+			Expect(s.BackendPreferenceTokens()).To(Equal(tc.wantTokens))
+		},
+		Entry("CUDA dir present but no GPU", testCase{
+			gpuVendor:      "",
+			vram:           0,
+			cuda12:         true,
+			cuda13:         false,
+			wantCapability: "default",
+			wantTokens:     []string{"cpu"},
+		}),
+		Entry("CUDA 12 with NVIDIA GPU", testCase{
+			gpuVendor:      Nvidia,
+			vram:           eightGB,
+			cuda12:         true,
+			cuda13:         false,
+			wantCapability: "nvidia-cuda-12",
+			wantTokens:     []string{"cuda", "vulkan", "cpu"},
+		}),
+		Entry("CUDA 13 with NVIDIA GPU", testCase{
+			gpuVendor:      Nvidia,
+			vram:           eightGB,
+			cuda12:         false,
+			cuda13:         true,
+			wantCapability: "nvidia-cuda-13",
+			wantTokens:     []string{"cuda", "vulkan", "cpu"},
+		}),
+		Entry("Both CUDA dirs with NVIDIA GPU prefers 13", testCase{
+			gpuVendor:      Nvidia,
+			vram:           eightGB,
+			cuda12:         true,
+			cuda13:         true,
+			wantCapability: "nvidia-cuda-13",
+			wantTokens:     []string{"cuda", "vulkan", "cpu"},
+		}),
+		Entry("CUDA dir with AMD GPU ignored", testCase{
+			gpuVendor:      AMD,
+			vram:           eightGB,
+			cuda12:         true,
+			cuda13:         false,
+			wantCapability: "amd",
+			wantTokens:     []string{"rocm", "hip", "vulkan", "cpu"},
+		}),
+		Entry("No CUDA dir and no GPU", testCase{
+			gpuVendor:      "",
+			vram:           0,
+			cuda12:         false,
+			cuda13:         false,
+			wantCapability: "default",
+			wantTokens:     []string{"cpu"},
+		}),
+		Entry("No CUDA dir with NVIDIA GPU", testCase{
+			gpuVendor:      Nvidia,
+			vram:           eightGB,
+			cuda12:         false,
+			cuda13:         false,
+			wantCapability: "nvidia",
+			wantTokens:     []string{"cuda", "vulkan", "cpu"},
+		}),
+		Entry("CUDA dir with NVIDIA GPU but low VRAM", testCase{
+			gpuVendor:      Nvidia,
+			vram:           twoGB,
+			cuda12:         true,
+			cuda13:         false,
+			wantCapability: "default",
+			wantTokens:     []string{"cpu"},
+		}),
+	)
+})

pkg/system/system_suite_test.go

@@ -0,0 +1,13 @@
+package system
+
+import (
+	"testing"
+
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+func TestSystem(t *testing.T) {
+	RegisterFailHandler(Fail)
+	RunSpecs(t, "System test suite")
+}