Implement final fixes and close out the implemetation roadmap

internal/framework/pipeline/artifact_codec_registry.go

@@ -67,7 +67,7 @@ type artifactCodecEntry struct {
 	valueType       reflect.Type
 	encode          func(any) ([]byte, error)
 	encodeCandidate func(any) ([]byte, error)
-	metadata        func(any) map[string]any
+	metadata        func(any) (map[string]any, error)
 	decode          func([]byte) (any, error)
 }
 
@@ -132,10 +132,10 @@ func RegisterArtifactCodec[T any](registry *ArtifactCodecRegistry, codec contrac
 		return append([]byte(nil), content...), nil
 	}
 	if provider, ok := any(codec).(interface{ Metadata(T) map[string]any }); ok {
-		entry.metadata = func(value any) map[string]any {
+		entry.metadata = func(value any) (map[string]any, error) {
 			typed, err := exactTypedValue[T]("artifact metadata", value)
 			if err != nil {
-				return nil
+				return nil, err
 			}
 			return cloneMetadata(provider.Metadata(typed))
 		}