Strengthen validation retries and checkpoint safety

internal/modules/dnd/validate/itemregistry/source_refs/validator.go

@@ -97,5 +97,5 @@ func DecodeOptions(options map[string]any) (Options, error) {
 func validateOptions(options map[string]any) error { _, err := DecodeOptions(options); return err }
 
 func rejection(message string) contracts.ValidationResult {
-	return contracts.ValidationResult{Approved: false, ReasonCode: ReasonCode, Message: message}
+	return contracts.ValidationResult{Approved: false, ReasonCode: ReasonCode, Message: message, CorrectionGuidance: "Return registry items whose source references identify valid transcript ranges within the supplied extraction chunk and directly support each named item."}
 }