Implement ordered pipeline step resolution

internal/framework/pipeline/module.go

@@ -133,6 +133,7 @@ func normalizeReferenceSlots(slots []contracts.ReferenceSlot) []contracts.Refere
 		slot.Name = strings.TrimSpace(slot.Name)
 		slot.Description = strings.TrimSpace(slot.Description)
 		slot.AcceptedMediaTypes = normalizeStringSet(slot.AcceptedMediaTypes)
+		slot.AcceptedArtifactKinds = normalizeArtifactKinds(slot.AcceptedArtifactKinds)
 		normalized = append(normalized, slot)
 	}
 	sort.SliceStable(normalized, func(i, j int) bool {
@@ -141,6 +142,34 @@ func normalizeReferenceSlots(slots []contracts.ReferenceSlot) []contracts.Refere
 	return normalized
 }
 
+func normalizeArtifactKinds(values []contracts.ArtifactKind) []contracts.ArtifactKind {
+	if len(values) == 0 {
+		return nil
+	}
+	seen := make(map[contracts.ArtifactKind]struct{}, len(values))
+	containsEmpty := false
+	for _, value := range values {
+		value = normalizeArtifactKind(value)
+		if value != "" {
+			seen[value] = struct{}{}
+		} else {
+			containsEmpty = true
+		}
+	}
+	if len(seen) == 0 && !containsEmpty {
+		return nil
+	}
+	result := make([]contracts.ArtifactKind, 0, len(seen))
+	for value := range seen {
+		result = append(result, value)
+	}
+	if containsEmpty {
+		result = append(result, "")
+	}
+	sort.Slice(result, func(i, j int) bool { return result[i] < result[j] })
+	return result
+}
+
 func normalizeStringSet(values []string) []string {
 	if len(values) == 0 {
 		return nil
@@ -178,6 +207,11 @@ func validateReferenceSlots(slots []contracts.ReferenceSlot) error {
 		if slot.MaxBytes < 0 {
 			return fmt.Errorf("slot %q max_bytes must not be negative", slot.Name)
 		}
+		for _, kind := range slot.AcceptedArtifactKinds {
+			if normalizeArtifactKind(kind) == "" {
+				return fmt.Errorf("slot %q accepted artifact kind must not be empty", slot.Name)
+			}
+		}
 	}
 	return nil
 }