fix(ops): preserve zero-valued system metrics

backend/internal/repository/ops_repo_metrics.go

@@ -114,37 +114,37 @@ INSERT INTO ops_system_metrics (
 		opsNullFloat64(input.QPS),
 		opsNullFloat64(input.TPS),
 
-		opsNullInt(input.DurationP50Ms),
-		opsNullInt(input.DurationP90Ms),
-		opsNullInt(input.DurationP95Ms),
-		opsNullInt(input.DurationP99Ms),
+		opsNullMetricInt(input.DurationP50Ms),
+		opsNullMetricInt(input.DurationP90Ms),
+		opsNullMetricInt(input.DurationP95Ms),
+		opsNullMetricInt(input.DurationP99Ms),
 		opsNullFloat64(input.DurationAvgMs),
-		opsNullInt(input.DurationMaxMs),
+		opsNullMetricInt(input.DurationMaxMs),
 
-		opsNullInt(input.TTFTP50Ms),
-		opsNullInt(input.TTFTP90Ms),
-		opsNullInt(input.TTFTP95Ms),
-		opsNullInt(input.TTFTP99Ms),
+		opsNullMetricInt(input.TTFTP50Ms),
+		opsNullMetricInt(input.TTFTP90Ms),
+		opsNullMetricInt(input.TTFTP95Ms),
+		opsNullMetricInt(input.TTFTP99Ms),
 		opsNullFloat64(input.TTFTAvgMs),
-		opsNullInt(input.TTFTMaxMs),
+		opsNullMetricInt(input.TTFTMaxMs),
 
 		opsNullFloat64(input.CPUUsagePercent),
-		opsNullInt(input.MemoryUsedMB),
-		opsNullInt(input.MemoryTotalMB),
+		opsNullMetricInt64(input.MemoryUsedMB),
+		opsNullMetricInt64(input.MemoryTotalMB),
 		opsNullFloat64(input.MemoryUsagePercent),
 
 		opsNullBool(input.DBOK),
 		opsNullBool(input.RedisOK),
 
-		opsNullInt(input.RedisConnTotal),
-		opsNullInt(input.RedisConnIdle),
+		opsNullMetricInt(input.RedisConnTotal),
+		opsNullMetricInt(input.RedisConnIdle),
 
-		opsNullInt(input.DBConnActive),
-		opsNullInt(input.DBConnIdle),
-		opsNullInt(input.DBConnWaiting),
+		opsNullMetricInt(input.DBConnActive),
+		opsNullMetricInt(input.DBConnIdle),
+		opsNullMetricInt(input.DBConnWaiting),
 
-		opsNullInt(input.GoroutineCount),
-		opsNullInt(input.ConcurrencyQueueDepth),
+		opsNullMetricInt(input.GoroutineCount),
+		opsNullMetricInt(input.ConcurrencyQueueDepth),
 	)
 	return err
 }
@@ -437,6 +437,20 @@ func opsNullFloat64(v *float64) any {
 	return sql.NullFloat64{Float64: *v, Valid: true}
 }
 
+func opsNullMetricInt(v *int) any {
+	if v == nil {
+		return sql.NullInt64{}
+	}
+	return sql.NullInt64{Int64: int64(*v), Valid: true}
+}
+
+func opsNullMetricInt64(v *int64) any {
+	if v == nil {
+		return sql.NullInt64{}
+	}
+	return sql.NullInt64{Int64: *v, Valid: true}
+}
+
 func opsNullTime(v *time.Time) any {
 	if v == nil || v.IsZero() {
 		return sql.NullTime{}

backend/internal/repository/ops_repo_metrics_test.go

@@ -0,0 +1,59 @@
+package repository
+
+import (
+	"context"
+	"database/sql/driver"
+	"testing"
+	"time"
+
+	"github.com/DATA-DOG/go-sqlmock"
+	"github.com/Wei-Shaw/sub2api/internal/service"
+)
+
+func TestInsertSystemMetricsNullableIntegerMetrics(t *testing.T) {
+	createdAt := time.Date(2026, time.September, 4, 12, 0, 0, 0, time.UTC)
+	zero := 0
+
+	tests := []struct {
+		name         string
+		dbConnActive *int
+		wantDBActive driver.Value
+	}{
+		{name: "explicit zero is preserved", dbConnActive: &zero, wantDBActive: int64(0)},
+		{name: "unavailable metric remains null", dbConnActive: nil, wantDBActive: nil},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			db, mock, err := sqlmock.New()
+			if err != nil {
+				t.Fatalf("sqlmock.New: %v", err)
+			}
+			t.Cleanup(func() { _ = db.Close() })
+
+			args := make([]driver.Value, 40)
+			args[0] = createdAt
+			args[1] = int64(1)
+			for i := 4; i <= 12; i++ {
+				args[i] = int64(0)
+			}
+			args[35] = tt.wantDBActive
+
+			mock.ExpectExec("INSERT INTO ops_system_metrics").
+				WithArgs(args...).
+				WillReturnResult(sqlmock.NewResult(1, 1))
+
+			repo := &opsRepository{db: db}
+			err = repo.InsertSystemMetrics(context.Background(), &service.OpsInsertSystemMetricsInput{
+				CreatedAt:    createdAt,
+				DBConnActive: tt.dbConnActive,
+			})
+			if err != nil {
+				t.Fatalf("InsertSystemMetrics: %v", err)
+			}
+			if err := mock.ExpectationsWereMet(); err != nil {
+				t.Fatalf("unmet SQL expectations: %v", err)
+			}
+		})
+	}
+}