Add structured validation failures

internal/candidate/check_test.go

@@ -9,6 +9,8 @@ import (
 	"path/filepath"
 	"strings"
 	"testing"
+
+	"gitea.maximumdirect.net/eric/ReleaseKit/internal/validation"
 )
 
 const testVersion = "v1.2.3"
@@ -123,6 +125,14 @@ func TestDefaultValidationDoesNotInheritGOFLAGSRunFilter(t *testing.T) {
 			if err == nil || !strings.Contains(output.String(), "TestExpectedFailure") {
 				t.Fatalf("Check() error = %v, output = %q; wanted the failing standard test to run", err, output.String())
 			}
+			var failure *validation.Failure
+			if !errors.As(err, &failure) || failure.Check != validation.GoTest {
+				t.Fatalf("Check() error = %v; want a go-test validation failure", err)
+			}
+			var exitErr *exec.ExitError
+			if !errors.As(err, &exitErr) {
+				t.Fatalf("Check() error = %v; want the Go process exit error preserved", err)
+			}
 		})
 	}
 }