Add type-safe artifact lane resolution

internal/framework/pipeline/module.go

@@ -23,6 +23,7 @@ const (
 type ModuleSpec struct {
 	Key            string
 	Stage          ModuleStage
+	ArtifactKind   contracts.ArtifactKind
 	Provides       []string
 	Requires       []string
 	ReferenceSlots []contracts.ReferenceSlot
@@ -39,6 +40,7 @@ func normalizeModuleSpec(spec ModuleSpec) ModuleSpec {
 	return ModuleSpec{
 		Key:            strings.TrimSpace(spec.Key),
 		Stage:          spec.Stage,
+		ArtifactKind:   normalizeArtifactKind(spec.ArtifactKind),
 		Provides:       normalizeCapabilities(spec.Provides),
 		Requires:       normalizeCapabilities(spec.Requires),
 		ReferenceSlots: normalizeReferenceSlots(spec.ReferenceSlots),
@@ -74,6 +76,7 @@ func cloneModuleSpec(spec ModuleSpec) ModuleSpec {
 	return ModuleSpec{
 		Key:            spec.Key,
 		Stage:          spec.Stage,
+		ArtifactKind:   spec.ArtifactKind,
 		Provides:       append([]string(nil), spec.Provides...),
 		Requires:       append([]string(nil), spec.Requires...),
 		ReferenceSlots: contracts.CloneReferenceSlots(spec.ReferenceSlots),
@@ -87,6 +90,9 @@ func validateModuleSpec(kind string, expectedStage ModuleStage, spec ModuleSpec)
 	if spec.Stage != expectedStage {
 		return fmt.Errorf("%s %q must use %q stage, got %q", kind, spec.Key, expectedStage, spec.Stage)
 	}
+	if spec.ArtifactKind != "" && spec.Stage != StageExtract && spec.Stage != StageMerge && spec.Stage != StageNormalize {
+		return fmt.Errorf("%s %q must not declare an artifact kind", kind, spec.Key)
+	}
 	if !referenceSlotStage(spec.Stage) && len(spec.ReferenceSlots) > 0 {
 		return fmt.Errorf("%s %q must not declare reference slots", kind, spec.Key)
 	}
@@ -113,6 +119,10 @@ func sortedRegistryKeys[C any](constructors map[string]C) []string {
 	return keys
 }
 
+func sortArtifactKinds(kinds []contracts.ArtifactKind) {
+	sort.Slice(kinds, func(i, j int) bool { return kinds[i] < kinds[j] })
+}
+
 func normalizeReferenceSlots(slots []contracts.ReferenceSlot) []contracts.ReferenceSlot {
 	if len(slots) == 0 {
 		return nil