Strengthen validation retries and checkpoint safety

internal/modules/dnd/validate/spells/catalog/validator.go

@@ -98,7 +98,7 @@ func rejection(unknown []unknownSpell) contracts.ValidationResult {
 		issues = append(issues, issue)
 	}
 	message := rejectionMessage(issues, len(unknown)-len(issues))
-	return contracts.ValidationResult{Approved: false, ReasonCode: ReasonCode, Message: message}
+	return contracts.ValidationResult{Approved: false, ReasonCode: ReasonCode, Message: message, CorrectionGuidance: "Use recognized D&D spell names supported by the supplied transcript evidence, and omit any candidate that is not a spell cast."}
 }
 
 func truncateDisplayedName(name string) string {

internal/modules/dnd/validate/spells/catalog/validator_test.go

@@ -54,6 +54,9 @@ func TestValidatorRejectsMultipleUnknownCastsInStableOrder(t *testing.T) {
 	if result.Approved || result.ReasonCode != ReasonCode {
 		t.Fatalf("Validate() = %#v, want unknown-spell rejection", result)
 	}
+	if err := contracts.ValidateValidationResult(result); err != nil {
+		t.Fatalf("ValidateValidationResult() error = %v for %#v", err, result)
+	}
 	if want := `spell_casts[0].spell "Unknown First", spell_casts[2].spell "Unknown Second"`; !strings.Contains(result.Message, want) {
 		t.Fatalf("message = %q, want %q", result.Message, want)
 	}