From a3197e214646565aea516251579070f9ba8a21b8 Mon Sep 17 00:00:00 2001
From: Sakurasan <26715255+Sakurasan@users.noreply.github.com>
Date: Fri, 30 Oct 2026 01:21:43 +0800
Subject: [PATCH] =?UTF-8?q?fix:=20=E8=AE=B0=E8=B4=A6=E5=90=8C=E4=B8=80=20t?=
 =?UTF-8?q?race=20=E9=98=B2=E9=87=8D=E5=A4=8D=E6=89=A3=E6=AC=BE?=
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流水 ref_id 有唯一索引，但扣款本身没有：重试/重复 flush 场景下
同一 trace 会被重复扣钱。billUser 扣款前先查 ref_id 是否已存在。
在远端记账重写基础上合并防重检查与测试。
---
 server/internal/usage/usage.go      |  7 +++++++
 server/internal/usage/usage_test.go | 29 +++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/server/internal/usage/usage.go b/server/internal/usage/usage.go
index 4f80dc3..61518ec 100644
--- a/server/internal/usage/usage.go
+++ b/server/internal/usage/usage.go
@@ -158,6 +158,13 @@ func (r *Recorder) billUser(tx *gorm.DB, l *store.UsageLog) error {
 		return err
 	}
 	// 余额允许为负（流式请求不中断；后续请求被 402 拒），所以 WHERE 只按 id 匹配
+	// 同一 trace 已记过账（重试/重复 flush）则跳过：流水 ref_id 有唯一索引，
+	// 但扣款本身没有，不挡住会重复扣钱
+	var billed int64
+	tx.Model(&store.BalanceLog{}).Where("ref_id = ?", usageRefID(l.TraceID)).Count(&billed)
+	if billed > 0 {
+		return nil
+	}
 	res := tx.Model(&store.User{}).Where("id = ?", l.UserID).Update("balance", gorm.Expr("balance - ?", l.Cost))
 	if res.Error != nil {
 		return res.Error
diff --git a/server/internal/usage/usage_test.go b/server/internal/usage/usage_test.go
index 8926673..773f7fb 100644
--- a/server/internal/usage/usage_test.go
+++ b/server/internal/usage/usage_test.go
@@ -141,3 +141,32 @@ func seedModel(t *testing.T, db *gorm.DB) uint64 {
 }
 
 func strPtr(s string) *string { return &s }
+
+// 同一 trace 重复记账（重试/重复 flush 场景）只扣一次款：流水 ref_id 有唯一索引，
+// 但扣款本身没有，billUser 必须先查再扣。
+func TestBillingRefIDImpotency(t *testing.T) {
+	db := openTestDB(t)
+	u := seedUser(t, db, 5)
+
+	rec := NewRecorder(db)
+	mk := func(trace string) *store.UsageLog {
+		return &store.UsageLog{TraceID: trace, UserID: u, ModelName: "m1",
+			Status: store.UsageStatusSuccess, Cost: 1, CreatedAt: time.Now().UTC()}
+	}
+	rec.Record(mk("dup"))
+	rec.Record(mk("dup"))
+	rec.Close()
+
+	var user store.User
+	if err := db.First(&user, u).Error; err != nil {
+		t.Fatal(err)
+	}
+	if user.Balance != 4 {
+		t.Errorf("balance = %v, want 4 (重复 trace 不重复扣款)", user.Balance)
+	}
+	var n int64
+	db.Model(&store.BalanceLog{}).Where("user_id = ?", u).Count(&n)
+	if n != 1 {
+		t.Errorf("balance logs = %d, want 1", n)
+	}
+}