fix(billing): settle usage when the API key is deleted before billing completes

When an API key with quota or rate limits was deleted while a request was
still in flight, the key counter update matched no rows and returned
ErrAPIKeyNotFound, rolling back the whole billing transaction including the
balance/subscription charge. Skip the key-scoped counters in that case and
keep settling the user and account side as usual.

backend/internal/repository/usage_billing_repo.go

@@ -187,16 +187,18 @@ func (r *usageBillingRepository) applyUsageBillingEffects(ctx context.Context, t
 		result.BalanceOverdrafted = !sufficient
 	}
 
+	// API Key 在请求进行中被删除时，其自身的额度/限速计数已无意义，跳过即可；
+	// 但用户余额、订阅与账号额度必须照常结算，不能因此回滚整个计费事务。
 	if cmd.APIKeyQuotaCost > 0 {
 		exhausted, err := incrementUsageBillingAPIKeyQuota(ctx, tx, cmd.APIKeyID, cmd.APIKeyQuotaCost)
-		if err != nil {
+		if err != nil && !errors.Is(err, service.ErrAPIKeyNotFound) {
 			return err
 		}
 		result.APIKeyQuotaExhausted = exhausted
 	}
 
 	if cmd.APIKeyRateLimitCost > 0 {
-		if err := incrementUsageBillingAPIKeyRateLimit(ctx, tx, cmd.APIKeyID, cmd.APIKeyRateLimitCost); err != nil {
+		if err := incrementUsageBillingAPIKeyRateLimit(ctx, tx, cmd.APIKeyID, cmd.APIKeyRateLimitCost); err != nil && !errors.Is(err, service.ErrAPIKeyNotFound) {
 			return err
 		}
 	}

backend/internal/repository/usage_billing_repo_integration_test.go

@@ -162,6 +162,61 @@ func TestUsageBillingRepositoryApply_RequestFingerprintConflict(t *testing.T) {
 	require.ErrorIs(t, err, service.ErrUsageBillingRequestConflict)
 }
 
+func TestUsageBillingRepositoryApply_DeletedAPIKeyStillBillsBalance(t *testing.T) {
+	ctx := context.Background()
+	client := testEntClient(t)
+	repo := NewUsageBillingRepository(client, integrationDB)
+
+	user := mustCreateUser(t, client, &service.User{
+		Email:        fmt.Sprintf("usage-billing-deleted-key-user-%d@example.com", time.Now().UnixNano()),
+		PasswordHash: "hash",
+		Balance:      100,
+	})
+	apiKey := mustCreateApiKey(t, client, &service.APIKey{
+		UserID:      user.ID,
+		Key:         "sk-usage-billing-deleted-key-" + uuid.NewString(),
+		Name:        "billing-deleted-key",
+		Quota:       50,
+		RateLimit5h: 50,
+	})
+	account := mustCreateAccount(t, client, &service.Account{
+		Name: "usage-billing-deleted-key-account-" + uuid.NewString(),
+		Type: service.AccountTypeAPIKey,
+	})
+
+	_, err := integrationDB.ExecContext(ctx, "UPDATE api_keys SET deleted_at = NOW() WHERE id = $1", apiKey.ID)
+	require.NoError(t, err)
+
+	requestID := uuid.NewString()
+	result, err := repo.Apply(ctx, &service.UsageBillingCommand{
+		RequestID:           requestID,
+		APIKeyID:            apiKey.ID,
+		UserID:              user.ID,
+		AccountID:           account.ID,
+		AccountType:         service.AccountTypeAPIKey,
+		BalanceCost:         1.25,
+		APIKeyQuotaCost:     1.25,
+		APIKeyRateLimitCost: 1.25,
+	})
+	require.NoError(t, err)
+	require.NotNil(t, result)
+	require.True(t, result.Applied)
+	require.False(t, result.APIKeyQuotaExhausted)
+
+	var balance float64
+	require.NoError(t, integrationDB.QueryRowContext(ctx, "SELECT balance FROM users WHERE id = $1", user.ID).Scan(&balance))
+	require.InDelta(t, 98.75, balance, 0.000001)
+
+	var quotaUsed, usage5h float64
+	require.NoError(t, integrationDB.QueryRowContext(ctx, "SELECT quota_used, usage_5h FROM api_keys WHERE id = $1", apiKey.ID).Scan(&quotaUsed, &usage5h))
+	require.InDelta(t, 0, quotaUsed, 0.000001)
+	require.InDelta(t, 0, usage5h, 0.000001)
+
+	var dedupCount int
+	require.NoError(t, integrationDB.QueryRowContext(ctx, "SELECT COUNT(*) FROM usage_billing_dedup WHERE request_id = $1 AND api_key_id = $2", requestID, apiKey.ID).Scan(&dedupCount))
+	require.Equal(t, 1, dedupCount)
+}
+
 func TestUsageBillingRepositoryApply_UpdatesAccountQuota(t *testing.T) {
 	ctx := context.Background()
 	client := testEntClient(t)

backend/internal/repository/usage_billing_repo_unit_test.go

@@ -20,6 +20,8 @@ const (
 	captureBatchImageHoldSQL    = `(?s)UPDATE users\s+SET balance = balance\s+\+ CASE WHEN \$1 > \$2 THEN \$1 - \$2 ELSE 0 END\s+- CASE WHEN \$2 > \$1 THEN \$2 - \$1 ELSE 0 END,\s+frozen_balance = COALESCE\(frozen_balance, 0\) - \$1,\s+updated_at = NOW\(\)\s+WHERE id = \$3 AND deleted_at IS NULL AND COALESCE\(frozen_balance, 0\) >= \$1\s+RETURNING balance, frozen_balance`
 	releaseBatchImageHoldSQL    = `(?s)UPDATE users\s+SET balance = balance \+ \$1,\s+frozen_balance = COALESCE\(frozen_balance, 0\) - \$1,\s+updated_at = NOW\(\)\s+WHERE id = \$2 AND deleted_at IS NULL AND COALESCE\(frozen_balance, 0\) >= \$1\s+RETURNING balance, frozen_balance`
 	userExistsForBillingSQL     = `(?s)SELECT 1\s+FROM users\s+WHERE id = \$1 AND deleted_at IS NULL`
+	apiKeyQuotaIncrementSQL     = `(?s)UPDATE api_keys\s+SET quota_used = quota_used \+ \$1,.*WHERE id = \$2 AND deleted_at IS NULL\s+RETURNING`
+	apiKeyRateLimitIncrementSQL = `(?s)UPDATE api_keys SET\s+usage_5h = .*WHERE id = \$2 AND deleted_at IS NULL`
 )
 
 func TestDeductUsageBillingBalance_UsesSufficientBalanceGuard(t *testing.T) {
@@ -99,6 +101,66 @@ func TestApplyUsageBillingEffects_FlagsBalanceOverdraft(t *testing.T) {
 	require.NoError(t, mock.ExpectationsWereMet())
 }
 
+func TestApplyUsageBillingEffects_DeletedAPIKeyStillBillsBalance(t *testing.T) {
+	ctx := context.Background()
+	db, mock, err := sqlmock.New()
+	require.NoError(t, err)
+	defer func() { _ = db.Close() }()
+
+	mock.ExpectBegin()
+	tx, err := db.BeginTx(ctx, nil)
+	require.NoError(t, err)
+	mock.ExpectQuery(conditionalBalanceDeductSQL).
+		WithArgs(10.0, int64(42)).
+		WillReturnRows(sqlmock.NewRows([]string{"balance"}).AddRow(90.0))
+	mock.ExpectQuery(apiKeyQuotaIncrementSQL).
+		WithArgs(10.0, int64(7), service.StatusAPIKeyActive, service.StatusAPIKeyQuotaExhausted).
+		WillReturnError(sql.ErrNoRows)
+	mock.ExpectExec(apiKeyRateLimitIncrementSQL).
+		WithArgs(10.0, int64(7)).
+		WillReturnResult(sqlmock.NewResult(0, 0))
+	mock.ExpectCommit()
+
+	result := &service.UsageBillingApplyResult{Applied: true}
+	err = (&usageBillingRepository{}).applyUsageBillingEffects(ctx, tx, &service.UsageBillingCommand{
+		UserID:              42,
+		APIKeyID:            7,
+		BalanceCost:         10,
+		APIKeyQuotaCost:     10,
+		APIKeyRateLimitCost: 10,
+	}, result)
+	require.NoError(t, err)
+	require.NotNil(t, result.NewBalance)
+	require.InDelta(t, 90.0, *result.NewBalance, 0.000001)
+	require.False(t, result.APIKeyQuotaExhausted)
+	require.NoError(t, tx.Commit())
+	require.NoError(t, mock.ExpectationsWereMet())
+}
+
+func TestApplyUsageBillingEffects_APIKeyCounterErrorStillFails(t *testing.T) {
+	ctx := context.Background()
+	db, mock, err := sqlmock.New()
+	require.NoError(t, err)
+	defer func() { _ = db.Close() }()
+
+	mock.ExpectBegin()
+	tx, err := db.BeginTx(ctx, nil)
+	require.NoError(t, err)
+	mock.ExpectExec(apiKeyRateLimitIncrementSQL).
+		WithArgs(10.0, int64(7)).
+		WillReturnError(sql.ErrConnDone)
+	mock.ExpectRollback()
+
+	err = (&usageBillingRepository{}).applyUsageBillingEffects(ctx, tx, &service.UsageBillingCommand{
+		UserID:              42,
+		APIKeyID:            7,
+		APIKeyRateLimitCost: 10,
+	}, &service.UsageBillingApplyResult{Applied: true})
+	require.ErrorIs(t, err, sql.ErrConnDone)
+	require.NoError(t, tx.Rollback())
+	require.NoError(t, mock.ExpectationsWereMet())
+}
+
 func TestDeductUsageBillingBalance_ReturnsUserNotFoundWhenNoUserUpdated(t *testing.T) {
 	ctx := context.Background()
 	db, mock, err := sqlmock.New()