Strengthen validation retries and checkpoint safety

internal/modules/dnd/validate/locationregistry/identity/validator.go

@@ -47,8 +47,10 @@ func (v *Validator) Validate(_ context.Context, req contracts.TypedValidationReq
 		issues[index] = fmt.Sprintf("locations[%d] %s: %s", issue.RecordIndex, issue.Code, diagnostics.Quote(issue.Value))
 	}
 	return contracts.ValidationResult{
-		Approved: false, ReasonCode: ReasonCode,
-		Message: diagnostics.Aggregate("invalid location identity", issues),
+		Approved:           false,
+		ReasonCode:         ReasonCode,
+		Message:            diagnostics.Aggregate("invalid location identity", issues),
+		CorrectionGuidance: "Return one canonical registry entry per distinct proper location name, combining duplicate mentions of the same location.",
 	}, nil
 }