Strengthen validation retries and checkpoint safety

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

@@ -49,9 +49,10 @@ func (v *Validator) Validate(_ context.Context, req contracts.TypedValidationReq
 		return contracts.ValidationResult{Approved: true}, nil
 	}
 	return contracts.ValidationResult{
-		Approved:   false,
-		ReasonCode: ReasonCode,
-		Message:    diagnostics.Aggregate("invalid combat turn source references", issues),
+		Approved:           false,
+		ReasonCode:         ReasonCode,
+		Message:            diagnostics.Aggregate("invalid combat turn source references", issues),
+		CorrectionGuidance: "Return combat turns whose source references identify valid transcript ranges within the supplied extraction chunk and directly support each turn.",
 	}, nil
 }