Serialize typed artifacts at durable boundaries

internal/framework/contracts/artifact.go

@@ -27,6 +27,15 @@ type SerializedArtifact struct {
 	Metadata  map[string]any `json:"metadata,omitempty"`
 }
 
+// SerializedOutput associates a domain-neutral artifact with the pipeline
+// operation that produced it. Provenance remains outside codec-owned bytes.
+type SerializedOutput struct {
+	LaneID        string             `json:"lane_id"`
+	NormalizerKey string             `json:"normalizer_key"`
+	SourceID      string             `json:"source_id,omitempty"`
+	Artifact      SerializedArtifact `json:"artifact"`
+}
+
 // ArtifactCodec owns the stable encoding for one concrete artifact type.
 type ArtifactCodec[T any] interface {
 	Kind() ArtifactKind
@@ -55,6 +64,11 @@ func CloneSerializedArtifact(artifact SerializedArtifact) SerializedArtifact {
 	return artifact
 }
 
+func CloneSerializedOutput(output SerializedOutput) SerializedOutput {
+	output.Artifact = CloneSerializedArtifact(output.Artifact)
+	return output
+}
+
 func cloneArtifactMetadata(metadata map[string]any) map[string]any {
 	if len(metadata) == 0 {
 		return nil