fix(lint): make compatibility test assertions fatal

backend/internal/service/gemini_messages_compat_service_test.go

@@ -782,9 +782,7 @@ func TestExtractGeminiUsage(t *testing.T) {
 				}
 				return
 			}
-			if got == nil {
-				t.Fatalf("期望返回非 nil，实际返回 nil")
-			}
+			require.NotNil(t, got)
 			if got.InputTokens != tt.wantUsage.InputTokens {
 				t.Errorf("InputTokens: 期望 %d，实际 %d", tt.wantUsage.InputTokens, got.InputTokens)
 			}

backend/internal/service/openai_gateway_service_codex_snapshot_test.go

@@ -3,6 +3,8 @@ package service
 import (
 	"testing"
 	"time"
+
+	"github.com/stretchr/testify/require"
 )
 
 func TestCodexSnapshotBaseTime(t *testing.T) {
@@ -50,9 +52,7 @@ func TestCodexResetAtRFC3339(t *testing.T) {
 	t.Run("positive seconds", func(t *testing.T) {
 		sec := 90
 		got := codexResetAtRFC3339(base, &sec)
-		if got == nil {
-			t.Fatal("expected non-nil")
-		}
+		require.NotNil(t, got)
 		if *got != "2026-02-16T10:01:30Z" {
 			t.Fatalf("got %s, want %s", *got, "2026-02-16T10:01:30Z")
 		}
@@ -61,9 +61,7 @@ func TestCodexResetAtRFC3339(t *testing.T) {
 	t.Run("negative seconds clamp to base", func(t *testing.T) {
 		sec := -3
 		got := codexResetAtRFC3339(base, &sec)
-		if got == nil {
-			t.Fatal("expected non-nil")
-		}
+		require.NotNil(t, got)
 		if *got != "2026-02-16T10:00:00Z" {
 			t.Fatalf("got %s, want %s", *got, "2026-02-16T10:00:00Z")
 		}