fix(build): emit legacy vnd.cnai.* identifiers for registry compat

PR #415 switched modctl from dragonflyoss/model-spec to modelpack/
model-spec, which moved every wire-format identifier from the
vnd.cnai.* / org.cnai.* family to vnd.cncf.* / org.cncf.*. Registries
whose MODEL artifact processor is still keyed on the legacy
identifiers cannot dispatch the new manifests and return
"processor for artifact MODEL not found" on /additions/* endpoints.

Centralize the legacy identifiers in pkg/backend/build/legacy.go and
point every build-path write site at them: manifest artifactType,
config blob mediaType, the eight layer mediaTypes, layer annotations
(filepath, file metadata), the manifest-level modctl modelfile
annotation, plus two raw-weight cache-key compares in
computeDigestAndSize so the digest cache stays consistent with the
emitted strings.

The Go-level modelspec package and the read/inspect paths
(inspect.go, pull.go, fetch.go, attach.go, codec/raw.go) are
untouched, so artifacts produced by either identifier family
remain readable.

Delete pkg/backend/build/legacy.go and revert the call sites to
modelspec.* once downstream registries register processors for the
modelpack identifiers.

Signed-off-by: Zhao Chen <winters.zc@antgroup.com>

Author: aftersnow

pkg/backend/build.go

@@ -24,7 +24,6 @@ import (
 	"path/filepath"
 
 	retry "github.com/avast/retry-go/v4"
-	modelspec "github.com/modelpack/model-spec/specs-go/v1"
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 	"github.com/sirupsen/logrus"
 
@@ -40,7 +39,9 @@ import (
 
 const (
 	// annotationModelfile is the annotation key for the Modelfile.
-	annotationModelfile = "org.cncf.modctl.modelfile"
+	// Uses the legacy "org.cnai.*" prefix to remain compatible with registry
+	// processors keyed on the pre-CNCF identifiers; see pkg/backend/build/legacy.go.
+	annotationModelfile = "org.cnai.modctl.modelfile"
 )
 
 // Build builds the user materials into the model artifact which follows the Model Spec.
@@ -166,33 +167,33 @@ func (b *backend) getProcessors(modelfile modelfile.Modelfile, cfg *config.Build
 	processors := []processor.Processor{}
 
 	if configs := modelfile.GetConfigs(); len(configs) > 0 {
-		mediaType := modelspec.MediaTypeModelWeightConfig
+		mediaType := build.LegacyMediaTypeModelWeightConfig
 		if cfg.Raw {
-			mediaType = modelspec.MediaTypeModelWeightConfigRaw
+			mediaType = build.LegacyMediaTypeModelWeightConfigRaw
 		}
 		processors = append(processors, processor.NewModelConfigProcessor(b.store, mediaType, configs, ""))
 	}
 
 	if models := modelfile.GetModels(); len(models) > 0 {
-		mediaType := modelspec.MediaTypeModelWeight
+		mediaType := build.LegacyMediaTypeModelWeight
 		if cfg.Raw {
-			mediaType = modelspec.MediaTypeModelWeightRaw
+			mediaType = build.LegacyMediaTypeModelWeightRaw
 		}
 		processors = append(processors, processor.NewModelProcessor(b.store, mediaType, models, ""))
 	}
 
 	if codes := modelfile.GetCodes(); len(codes) > 0 {
-		mediaType := modelspec.MediaTypeModelCode
+		mediaType := build.LegacyMediaTypeModelCode
 		if cfg.Raw {
-			mediaType = modelspec.MediaTypeModelCodeRaw
+			mediaType = build.LegacyMediaTypeModelCodeRaw
 		}
 		processors = append(processors, processor.NewCodeProcessor(b.store, mediaType, codes, ""))
 	}
 
 	if docs := modelfile.GetDocs(); len(docs) > 0 {
-		mediaType := modelspec.MediaTypeModelDoc
+		mediaType := build.LegacyMediaTypeModelDoc
 		if cfg.Raw {
-			mediaType = modelspec.MediaTypeModelDocRaw
+			mediaType = build.LegacyMediaTypeModelDocRaw
 		}
 		processors = append(processors, processor.NewDocProcessor(b.store, mediaType, docs, ""))
 	}

pkg/backend/build/builder.go

@@ -218,7 +218,7 @@ func (ab *abstractBuilder) BuildConfig(ctx context.Context, config modelspec.Mod
 	}
 
 	digest := fmt.Sprintf("sha256:%x", sha256.Sum256(configJSON))
-	return ab.strategy.OutputConfig(ctx, modelspec.MediaTypeModelConfig, digest, int64(len(configJSON)), bytes.NewReader(configJSON), hooks)
+	return ab.strategy.OutputConfig(ctx, LegacyMediaTypeModelConfig, digest, int64(len(configJSON)), bytes.NewReader(configJSON), hooks)
 }
 
 func (ab *abstractBuilder) BuildManifest(ctx context.Context, layers []ocispec.Descriptor, config ocispec.Descriptor, annotations map[string]string, hooks hooks.Hooks) (ocispec.Descriptor, error) {
@@ -227,7 +227,7 @@ func (ab *abstractBuilder) BuildManifest(ctx context.Context, layers []ocispec.D
 			SchemaVersion: 2,
 		},
 		Annotations:  annotations,
-		ArtifactType: modelspec.ArtifactTypeModelManifest,
+		ArtifactType: LegacyArtifactTypeModelManifest,
 		Config: ocispec.Descriptor{
 			MediaType: config.MediaType,
 			Digest:    config.Digest,
@@ -249,7 +249,7 @@ func (ab *abstractBuilder) BuildManifest(ctx context.Context, layers []ocispec.D
 // computeDigestAndSize computes the digest and size for the encoded content, using cache if available.
 func (ab *abstractBuilder) computeDigestAndSize(ctx context.Context, mediaType, path, workDirPath string, info os.FileInfo, reader io.Reader, codec pkgcodec.Codec) (io.Reader, string, int64, error) {
 	// Try to retrieve valid digest from cache for raw model weights.
-	if mediaType == modelspec.MediaTypeModelWeightRaw {
+	if mediaType == LegacyMediaTypeModelWeightRaw {
 		if digest, size, ok := ab.retrieveCache(ctx, path, info); ok {
 			return reader, digest, size, nil
 		}
@@ -273,7 +273,7 @@ func (ab *abstractBuilder) computeDigestAndSize(ctx context.Context, mediaType,
 	}
 
 	// Update cache.
-	if mediaType == modelspec.MediaTypeModelWeightRaw {
+	if mediaType == LegacyMediaTypeModelWeightRaw {
 		if err := ab.updateCache(ctx, path, info.ModTime(), size, digest); err != nil {
 			logrus.Warnf("builder: failed to update cache for file %s: %s", path, err)
 		}
@@ -405,7 +405,7 @@ func addFileMetadata(desc *ocispec.Descriptor, path, relPath string) error {
 	if desc.Annotations == nil {
 		desc.Annotations = make(map[string]string)
 	}
-	desc.Annotations[modelspec.AnnotationFileMetadata] = string(metadataStr)
+	desc.Annotations[LegacyAnnotationFileMetadata] = string(metadataStr)
 	return nil
 }
 

pkg/backend/build/builder_test.go

@@ -29,7 +29,6 @@ import (
 	"testing"
 	"time"
 
-	modelspec "github.com/modelpack/model-spec/specs-go/v1"
 	godigest "github.com/opencontainers/go-digest"
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 	"github.com/stretchr/testify/assert"
@@ -148,7 +147,7 @@ func (s *BuilderTestSuite) TestBuildLayer() {
 func (s *BuilderTestSuite) TestBuildConfig() {
 	s.Run("successful build config", func() {
 		expectedDesc := ocispec.Descriptor{
-			MediaType: modelspec.MediaTypeModelConfig,
+			MediaType: LegacyMediaTypeModelConfig,
 			Digest:    "sha256:test",
 			Size:      100,
 		}
@@ -166,7 +165,7 @@ func (s *BuilderTestSuite) TestBuildConfig() {
 		config, err := BuildModelConfig(modelConfig, []ocispec.Descriptor{})
 		s.NoError(err)
 
-		s.mockOutputStrategy.On("OutputConfig", mock.Anything, modelspec.MediaTypeModelConfig, mock.Anything, mock.Anything, mock.Anything, mock.Anything).
+		s.mockOutputStrategy.On("OutputConfig", mock.Anything, LegacyMediaTypeModelConfig, mock.Anything, mock.Anything, mock.Anything, mock.Anything).
 			Return(expectedDesc, nil).Once()
 
 		desc, err := s.builder.BuildConfig(context.Background(), config, hooks.NewHooks())
@@ -190,7 +189,7 @@ func (s *BuilderTestSuite) TestBuildConfig() {
 		config, err := BuildModelConfig(modelConfig, []ocispec.Descriptor{})
 		s.NoError(err)
 
-		s.mockOutputStrategy.On("OutputConfig", mock.Anything, modelspec.MediaTypeModelConfig, mock.Anything, mock.Anything, mock.Anything, mock.Anything).
+		s.mockOutputStrategy.On("OutputConfig", mock.Anything, LegacyMediaTypeModelConfig, mock.Anything, mock.Anything, mock.Anything, mock.Anything).
 			Return(ocispec.Descriptor{}, errors.New("output error")).Once()
 
 		_, err = s.builder.BuildConfig(context.Background(), config, hooks.NewHooks())
@@ -209,7 +208,7 @@ func (s *BuilderTestSuite) TestBuildManifest() {
 			},
 		}
 		config := ocispec.Descriptor{
-			MediaType: modelspec.MediaTypeModelConfig,
+			MediaType: LegacyMediaTypeModelConfig,
 			Digest:    "sha256:config",
 			Size:      50,
 		}

pkg/backend/build/legacy.go

@@ -0,0 +1,48 @@
+/*
+ *     Copyright 2026 The ModelPack Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package build
+
+// Transitional wire-format identifiers (vnd.cnai.* / org.cnai.*).
+//
+// The source-of-truth model-spec moved from github.com/dragonflyoss/model-spec
+// (vnd.cnai.* / org.cnai.*) to github.com/modelpack/model-spec (vnd.cncf.* /
+// org.cncf.*) when the project graduated into the CNCF sandbox. Registries
+// that registered their MODEL artifact processor against the legacy
+// identifiers cannot dispatch vnd.cncf.* manifests and return
+// "processor for artifact MODEL not found" on /additions endpoints.
+//
+// These constants pin the wire-format strings emitted by modctl to the
+// legacy values for compatibility with such registries. Once downstream
+// registries register processors for the modelpack identifiers, delete
+// this file and switch the build-path call sites back to modelspec.*.
+const (
+	LegacyArtifactTypeModelManifest = "application/vnd.cnai.model.manifest.v1+json"
+
+	LegacyMediaTypeModelConfig = "application/vnd.cnai.model.config.v1+json"
+
+	LegacyMediaTypeModelWeight          = "application/vnd.cnai.model.weight.v1.tar"
+	LegacyMediaTypeModelWeightRaw       = "application/vnd.cnai.model.weight.v1.raw"
+	LegacyMediaTypeModelWeightConfig    = "application/vnd.cnai.model.weight.config.v1.tar"
+	LegacyMediaTypeModelWeightConfigRaw = "application/vnd.cnai.model.weight.config.v1.raw"
+	LegacyMediaTypeModelCode            = "application/vnd.cnai.model.code.v1.tar"
+	LegacyMediaTypeModelCodeRaw         = "application/vnd.cnai.model.code.v1.raw"
+	LegacyMediaTypeModelDoc             = "application/vnd.cnai.model.doc.v1.tar"
+	LegacyMediaTypeModelDocRaw          = "application/vnd.cnai.model.doc.v1.raw"
+
+	LegacyAnnotationFilepath     = "org.cnai.model.filepath"
+	LegacyAnnotationFileMetadata = "org.cnai.model.file.metadata+json"
+)

pkg/backend/build/local.go

@@ -21,7 +21,6 @@ import (
 	"fmt"
 	"io"
 
-	modelspec "github.com/modelpack/model-spec/specs-go/v1"
 	godigest "github.com/opencontainers/go-digest"
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 
@@ -63,7 +62,7 @@ func (lo *localOutput) OutputLayer(ctx context.Context, mediaType, relPath, dest
 		Digest:    godigest.Digest(digest),
 		Size:      size,
 		Annotations: map[string]string{
-			modelspec.AnnotationFilepath: destPath,
+			LegacyAnnotationFilepath: destPath,
 		},
 	}
 

pkg/backend/build/local_test.go

@@ -23,7 +23,6 @@ import (
 	"strings"
 	"testing"
 
-	modelspec "github.com/modelpack/model-spec/specs-go/v1"
 	godigest "github.com/opencontainers/go-digest"
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 	"github.com/stretchr/testify/mock"
@@ -78,7 +77,7 @@ func (s *LocalOutputTestSuite) TestOutputLayer() {
 		s.Equal("test/mediatype", desc.MediaType)
 		s.Equal(godigest.Digest(expectedDigest), desc.Digest)
 		s.Equal(expectedSize, desc.Size)
-		s.Equal("test-file.txt", desc.Annotations[modelspec.AnnotationFilepath])
+		s.Equal("test-file.txt", desc.Annotations[LegacyAnnotationFilepath])
 		s.mockStorage.AssertExpectations(s.T())
 	})
 

pkg/backend/build/remote.go

@@ -21,7 +21,6 @@ import (
 	"fmt"
 	"io"
 
-	modelspec "github.com/modelpack/model-spec/specs-go/v1"
 	godigest "github.com/opencontainers/go-digest"
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 
@@ -61,7 +60,7 @@ func (ro *remoteOutput) OutputLayer(ctx context.Context, mediaType, relPath, des
 		Digest:    godigest.Digest(digest),
 		Size:      size,
 		Annotations: map[string]string{
-			modelspec.AnnotationFilepath: destPath,
+			LegacyAnnotationFilepath: destPath,
 		},
 	}