fix: update CNCF model detection to use artifactType field in manifest

Author: ilopezluna

pkg/distribution/internal/bundle/unpack.go

@@ -40,14 +40,16 @@ func isV02Model(model types.ModelArtifact) bool {
 }
 
 // isCNCFModel checks if the model was packaged using the CNCF ModelPack format.
+// Detection uses the manifest's artifactType field, which is required by the
+// CNCF model-spec ("application/vnd.cncf.model.manifest.v1+json").
 // CNCF ModelPack uses a layer-per-file approach with filepath annotations,
 // similar to V0.2, so it can be unpacked using UnpackFromLayers.
 func isCNCFModel(model types.ModelArtifact) bool {
 	manifest, err := model.Manifest()
 	if err != nil {
 		return false
 	}
-	return manifest.Config.MediaType == modelpack.MediaTypeModelConfigV1
+	return manifest.ArtifactType == modelpack.ArtifactTypeModelManifest
 }
 
 // unpackLegacy is the original V0.1 unpacking logic that uses model.GGUFPaths(), model.SafetensorsPaths(), etc.

pkg/distribution/internal/bundle/unpack_test.go

@@ -235,11 +235,13 @@ func TestIsCNCFModel(t *testing.T) {
 	tests := []struct {
 		name            string
 		configMediaType oci.MediaType
+		artifactType    string
 		expected        bool
 	}{
 		{
 			name:            "CNCF ModelPack config V1",
 			configMediaType: modelpack.MediaTypeModelConfigV1,
+			artifactType:    modelpack.ArtifactTypeModelManifest,
 			expected:        true,
 		},
 		{
@@ -256,9 +258,10 @@ func TestIsCNCFModel(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			// Create a minimal artifact with the given config media type
+			// Create a minimal artifact with the given config media type and artifact type
 			artifact := &testArtifactWithConfigMediaType{
 				configMediaType: tt.configMediaType,
+				artifactType:    tt.artifactType,
 			}
 			result := isCNCFModel(artifact)
 			if result != tt.expected {
@@ -271,10 +274,12 @@ func TestIsCNCFModel(t *testing.T) {
 // testArtifactWithConfigMediaType is a minimal ModelArtifact for testing isCNCFModel/isV02Model.
 type testArtifactWithConfigMediaType struct {
 	configMediaType oci.MediaType
+	artifactType    string
 }
 
 func (a *testArtifactWithConfigMediaType) Manifest() (*oci.Manifest, error) {
 	return &oci.Manifest{
+		ArtifactType: a.artifactType,
 		Config: oci.Descriptor{
 			MediaType: a.configMediaType,
 		},

pkg/distribution/internal/partial/partial.go

@@ -357,13 +357,21 @@ func ManifestForLayers(i WithLayers) (*oci.Manifest, error) {
 		return nil, fmt.Errorf("get layers: %w", err)
 	}
 
+	type descriptorProvider interface {
+		GetDescriptor() oci.Descriptor
+	}
+
 	var layers []oci.Descriptor
 	for _, l := range ls {
 		// Check if this is our Layer type which embeds the full descriptor
 		// with annotations.
 		if layer, ok := l.(*Layer); ok {
 			// Use the embedded descriptor directly to preserve annotations.
 			layers = append(layers, layer.Descriptor)
+		} else if dp, ok := l.(descriptorProvider); ok {
+			// Use GetDescriptor() to preserve annotations from wrapper
+			// types like remappedLayer.
+			layers = append(layers, dp.GetDescriptor())
 		} else {
 			// Fall back to computing descriptor for other layer types.
 			mt, err := l.MediaType()