Require candidate decoders for artifact codecs

internal/framework/pipeline/artifact_codec_registry.go

@@ -69,6 +69,7 @@ type artifactCodecEntry struct {
 	encodeCandidate func(any) ([]byte, error)
 	metadata        func(any) (map[string]any, error)
 	decode          func([]byte) (any, error)
+	decodeCandidate func([]byte) (any, error)
 }
 
 func NewArtifactCodecRegistry() *ArtifactCodecRegistry {
@@ -77,7 +78,7 @@ func NewArtifactCodecRegistry() *ArtifactCodecRegistry {
 
 // RegisterArtifactCodec registers one codec for T. The concrete type is kept
 // private and checked at every erased encode boundary.
-func RegisterArtifactCodec[T any](registry *ArtifactCodecRegistry, codec contracts.ArtifactCodec[T]) error {
+func RegisterArtifactCodec[T any](registry *ArtifactCodecRegistry, codec contracts.CandidateArtifactCodec[T]) error {
 	if registry == nil {
 		return fmt.Errorf("artifact codec registry must not be nil")
 	}
@@ -119,6 +120,13 @@ func RegisterArtifactCodec[T any](registry *ArtifactCodecRegistry, codec contrac
 			}
 			return decoded, nil
 		},
+		decodeCandidate: func(content []byte) (any, error) {
+			decoded, err := codec.DecodeCandidate(append([]byte(nil), content...))
+			if err != nil {
+				return nil, &ArtifactCodecOperationError{Operation: "decode candidate", Kind: spec.Kind, Err: err}
+			}
+			return decoded, nil
+		},
 	}
 	entry.encodeCandidate = func(value any) ([]byte, error) {
 		typed, err := exactTypedValue[T]("encode candidate artifact", value)