fix(monitor): align quota-fetcher credential/balance semantics with scheduler

P2-1/P2-3 from review:

- fetchCNQuota: credential-invalid now judged by StatusCode 401/403
  (aligned with fetchCNBalance) instead of `!Success && !CredentialValid` —
  CN quota service only sets CredentialValid=true on the success path, so
  500/429/zhipu business errors were all misclassified as failed instead
  of error.
- fetchCNBalance: snapshot carries new BalanceLow flag computed with the
  scheduler's exact criterion (`!Available || allCNBalancesBelowThreshold`)
  against Gateway.CNProviders.BalanceThreshold (ctor now takes cfg; wire
  regenerated). quotaDegradedHint reports "balance low" instead of the old
  `<=0` check, so an account already paused by the scheduler (balance 5 /
  threshold 10) no longer shows green in the monitor.
- threshold helper falls back to viper default 0.5 for nil/<=0 config to
  avoid a zero-threshold regression where balance=0 stops alerting.

Tests: CN quota status-code matrix (rewrites the test that cemented the
old behavior), balance-low matrix (below-threshold / unavailable /
multi-currency healthy), threshold-from-config; PayG stubs now set
Available explicitly (zero-value trap).

backend/cmd/server/wire_gen.go

@@ -337,7 +337,7 @@ func initializeApplication(buildInfo handler.BuildInfo) (*Application, error) {
 	batchImageWorkerRuntime := service.ProvideBatchImageWorkerRuntime(batchImageRepository, accountRepository, batchImageQueue, usageBillingRepository, usageLogRepository, batchImageModelPricingResolver, apiKeyAuthCacheInvalidator, configConfig)
 	scheduledTestRunnerService := service.ProvideScheduledTestRunnerService(scheduledTestPlanRepository, scheduledTestService, accountTestService, rateLimitService, configConfig)
 	paymentOrderExpiryService := service.ProvidePaymentOrderExpiryService(paymentService, leaderLockCache, db)
-	channelMonitorQuotaFetcher := service.NewChannelMonitorQuotaFetcher(accountUsageService, cnProviderQuotaService, cnProviderBalanceService, accountRepository)
+	channelMonitorQuotaFetcher := service.NewChannelMonitorQuotaFetcher(accountUsageService, cnProviderQuotaService, cnProviderBalanceService, accountRepository, configConfig)
 	channelMonitorRunner := service.ProvideChannelMonitorRunner(channelMonitorService, settingService, channelMonitorQuotaFetcher)
 	channelMonitorV2Aggregator := service.ProvideChannelMonitorV2Aggregator(channelMonitorV2Repository, db, settingService)
 	userPlatformQuotaUsageFlusher := service.ProvideUserPlatformQuotaUsageFlusher(configConfig, billingCache, serviceUserPlatformQuotaRepository, timingWheelService)

backend/internal/domain/channel_monitor_quota.go

@@ -50,6 +50,10 @@ type MonitorQuotaSnapshot struct {
 	Balances  []MonitorBalance   `json:"balances,omitempty"`   // 多币种余额（如 DeepSeek CNY+USD）
 	Currency  string             `json:"currency,omitempty"`   // 主余额币种
 	PlanLevel string             `json:"plan_level,omitempty"` // 套餐等级（如智谱 level）
+	// BalanceLow 余额低于阈值或账号被上游标记不可用（仅 cn_balance 来源）。
+	// 抓取器按 Gateway.CNProviders.BalanceThreshold 判定，口径与账号停调
+	// （CNProviderBalanceCheckService.checkOne）一致：任一币种达标即健康。
+	BalanceLow bool `json:"balance_low,omitempty"`
 	// CredentialInvalid 上游 401/403 鉴权失败（区别于网络/解析错误），
 	// 检测状态据此推导 failed 而非 error。
 	CredentialInvalid bool      `json:"credential_invalid,omitempty"`

backend/internal/service/channel_monitor_quota_fetcher.go

@@ -10,6 +10,7 @@ import (
 	"sync"
 	"time"
 
+	"github.com/Wei-Shaw/sub2api/internal/config"
 	"github.com/Wei-Shaw/sub2api/internal/domain"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/xai"
 	"golang.org/x/sync/singleflight"
@@ -58,6 +59,8 @@ type ChannelMonitorQuotaFetcher struct {
 	cnQuota   monitorCNQuotaSource
 	cnBalance monitorCNBalanceSource
 	accounts  monitorAccountSource
+	// balanceThreshold cn_balance 余额告警阈值（与账号停调共用配置，见 monitorBalanceThreshold）。
+	balanceThreshold float64
 
 	mu     sync.Mutex
 	cache  map[int64]monitorQuotaCacheEntry
@@ -76,8 +79,12 @@ func NewChannelMonitorQuotaFetcher(
 	cnQuota *CNProviderQuotaService,
 	cnBalance *CNProviderBalanceService,
 	accounts AccountRepository,
+	cfg *config.Config,
 ) *ChannelMonitorQuotaFetcher {
-	f := &ChannelMonitorQuotaFetcher{cache: make(map[int64]monitorQuotaCacheEntry)}
+	f := &ChannelMonitorQuotaFetcher{
+		cache:            make(map[int64]monitorQuotaCacheEntry),
+		balanceThreshold: monitorBalanceThreshold(cfg),
+	}
 	if usage != nil {
 		f.usage = usage
 	}
@@ -93,6 +100,17 @@ func NewChannelMonitorQuotaFetcher(
 	return f
 }
 
+// monitorBalanceThreshold 余额告警阈值，与账号停调（CNProviderBalanceCheckService）
+// 共用 gateway.cn_providers.balance_threshold，保证监控 degraded 与调度器停调
+// 口径一致（任一币种达标即健康）。未配置/非正值时回退 viper 默认 0.5（config.go），
+// 避免 0 阈值下「余额=0 也不告警」相对旧 `<=0` 判定的回归。
+func monitorBalanceThreshold(cfg *config.Config) float64 {
+	if cfg != nil && cfg.Gateway.CNProviders.BalanceThreshold > 0 {
+		return cfg.Gateway.CNProviders.BalanceThreshold
+	}
+	return 0.5
+}
+
 // LoadAccount 加载账号（不走缓存）。供 Create/Update 时校验
 // provider 与 account.platform 一致；账号不存在时返回错误。
 func (f *ChannelMonitorQuotaFetcher) LoadAccount(ctx context.Context, id int64) (*Account, error) {
@@ -341,7 +359,10 @@ func (f *ChannelMonitorQuotaFetcher) fetchCNQuota(ctx context.Context, accountID
 		Error:     result.Error,
 		FetchedAt: now,
 	}
-	if !result.Success && !result.CredentialValid {
+	// 只有 401/403 判凭据失效（与 fetchCNBalance 口径一致）：CN quota 服务的
+	// CredentialValid 仅在成功路径置 true，若按 `!Success && !CredentialValid`
+	// 推导，500/429/智谱业务错误全会被误判为 failed。
+	if !result.Success && (result.StatusCode == 401 || result.StatusCode == 403) {
 		snapshot.CredentialInvalid = true
 	}
 	if len(result.Tiers) > 0 {
@@ -386,6 +407,10 @@ func (f *ChannelMonitorQuotaFetcher) fetchCNBalance(ctx context.Context, account
 	if result.Success {
 		balance := result.Balance
 		snapshot.Balance = &balance
+		// 与账号停调（checkOne）同口径：上游标记不可用或全部币种低于阈值
+		// 才告警，任一币种达标即健康（余额 5 元/阈值 10 元的账号调度器已
+		// 停调，监控不能仍绿灯）。
+		snapshot.BalanceLow = !result.Available || allCNBalancesBelowThreshold(result, f.balanceThreshold)
 	} else if result.StatusCode == 401 || result.StatusCode == 403 {
 		snapshot.CredentialInvalid = true
 	}
@@ -454,7 +479,7 @@ func usageFailureInfo(usage *UsageInfo) (failed, credentialInvalid bool, msg str
 // deriveQuotaCheckResult 把配额快照推导为检测状态（复用既有 status 枚举，
 // 时间线/可用率机制自动生效）：
 //   - 查询成功且无告警        → operational
-//   - 任一窗口使用率 >= 阈值或余额耗尽 → degraded
+//   - 任一窗口使用率 >= 阈值或余额低于阈值/不可用 → degraded
 //   - 账号未关联（配置问题）    → degraded
 //   - 凭据失效（401/403）     → failed
 //   - 网络/解析等其他错误      → error
@@ -499,8 +524,11 @@ func quotaDegradedHint(snapshot *domain.MonitorQuotaSnapshot) string {
 			return fmt.Sprintf("quota high: %s at %s%%", name, strconv.FormatFloat(tier.UsedPercent, 'f', 1, 64))
 		}
 	}
-	if snapshot.Balance != nil && *snapshot.Balance <= 0 {
-		return fmt.Sprintf("balance depleted (%s)", firstNonEmpty(snapshot.Currency, "?"))
+	if snapshot.BalanceLow {
+		if snapshot.Balance != nil {
+			return fmt.Sprintf("balance low: %s %s", strconv.FormatFloat(*snapshot.Balance, 'f', -1, 64), firstNonEmpty(snapshot.Currency, "?"))
+		}
+		return fmt.Sprintf("balance low (%s)", firstNonEmpty(snapshot.Currency, "?"))
 	}
 	return ""
 }

backend/internal/service/channel_monitor_quota_fetcher_test.go

@@ -9,6 +9,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/Wei-Shaw/sub2api/internal/config"
 	"github.com/Wei-Shaw/sub2api/internal/domain"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/xai"
 	"github.com/stretchr/testify/require"
@@ -87,11 +88,12 @@ func newQuotaFetcherTestSetup(t *testing.T) (*ChannelMonitorQuotaFetcher, *stubM
 	cnBalance := &stubMonitorCNBalanceSource{}
 	accounts := &stubMonitorAccountSource{accounts: make(map[int64]*Account)}
 	fetcher := &ChannelMonitorQuotaFetcher{
-		usage:     usage,
-		cnQuota:   cnQuota,
-		cnBalance: cnBalance,
-		accounts:  accounts,
-		cache:     make(map[int64]monitorQuotaCacheEntry),
+		usage:            usage,
+		cnQuota:          cnQuota,
+		cnBalance:        cnBalance,
+		accounts:         accounts,
+		balanceThreshold: monitorBalanceThreshold(nil),
+		cache:            make(map[int64]monitorQuotaCacheEntry),
 	}
 	return fetcher, usage, cnQuota, cnBalance, accounts
 }
@@ -167,9 +169,10 @@ func TestQuotaFetcher_PayGAccountUsesCNBalance(t *testing.T) {
 		Credentials: map[string]any{"account_mode": AccountModePayG},
 	}
 	cnBalance.result = &CNProviderBalanceResult{
-		Success:  true,
-		Balance:  12.34,
-		Currency: "CNY",
+		Success:   true,
+		Available: true,
+		Balance:   12.34,
+		Currency:  "CNY",
 		Balances: []CNProviderBalanceEntry{
 			{Currency: "CNY", Balance: 12.34},
 			{Currency: "USD", Balance: 1.5},
@@ -185,6 +188,7 @@ func TestQuotaFetcher_PayGAccountUsesCNBalance(t *testing.T) {
 	require.Equal(t, "CNY", snapshot.Currency)
 	require.Len(t, snapshot.Balances, 2)
 	require.Equal(t, "USD", snapshot.Balances[1].Currency)
+	require.False(t, snapshot.BalanceLow)
 	require.Empty(t, snapshot.Error)
 }
 
@@ -278,20 +282,44 @@ func TestUsageFailureInfo_ClassificationMatrix(t *testing.T) {
 	}
 }
 
-func TestQuotaFetcher_CNQuotaCredentialInvalidFlagPropagates(t *testing.T) {
-	fetcher, _, cnQuota, _, accounts := newQuotaFetcherTestSetup(t)
-	accounts.accounts[5] = &Account{
-		ID:          5,
-		Platform:    domain.PlatformZhipu,
-		Credentials: map[string]any{"account_mode": AccountModeCoding},
+// 凭据失效只认 401/403（与 fetchCNBalance 口径一致）：CN quota 服务的
+// CredentialValid 仅成功路径置 true，500/429/智谱业务错误须推导为 error 而非 failed。
+func TestQuotaFetcher_CNQuotaCredentialInvalidByStatusCode(t *testing.T) {
+	cases := []struct {
+		name           string
+		accountID      int64
+		statusCode     int
+		credentialBad  bool
+		expectedStatus string
+	}{
+		{name: "401 unauthorized", accountID: 5, statusCode: 401, credentialBad: true, expectedStatus: MonitorStatusFailed},
+		{name: "403 forbidden", accountID: 15, statusCode: 403, credentialBad: true, expectedStatus: MonitorStatusFailed},
+		{name: "500 server error", accountID: 16, statusCode: 500, expectedStatus: MonitorStatusError},
+		{name: "429 rate limited", accountID: 17, statusCode: 429, expectedStatus: MonitorStatusError},
+		// 智谱 2xx 但业务级失败：StatusCode=200，非凭据问题。
+		{name: "200 business error", accountID: 18, statusCode: 200, expectedStatus: MonitorStatusError},
 	}
-	cnQuota.result = &CNProviderQuotaProbeResult{Success: false, CredentialValid: false, Error: "api key expired"}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			fetcher, _, cnQuota, _, accounts := newQuotaFetcherTestSetup(t)
+			accounts.accounts[tc.accountID] = &Account{
+				ID:          tc.accountID,
+				Platform:    domain.PlatformZhipu,
+				Credentials: map[string]any{"account_mode": AccountModeCoding},
+			}
+			cnQuota.result = &CNProviderQuotaProbeResult{
+				Success:    false,
+				StatusCode: tc.statusCode,
+				Error:      "api key expired",
+			}
 
-	snapshot := fetcher.Fetch(context.Background(), 5)
+			snapshot := fetcher.Fetch(context.Background(), tc.accountID)
 
-	require.False(t, snapshot.Success)
-	require.True(t, snapshot.CredentialInvalid)
-	require.Equal(t, "api key expired", snapshot.Error)
+			require.False(t, snapshot.Success)
+			require.Equal(t, tc.credentialBad, snapshot.CredentialInvalid)
+			require.Equal(t, tc.expectedStatus, deriveQuotaCheckResult(snapshot, "quota", time.Now()).Status)
+		})
+	}
 }
 
 func TestQuotaFetcher_CNBalanceHTTP403MarksCredentialInvalid(t *testing.T) {
@@ -305,6 +333,86 @@ func TestQuotaFetcher_CNBalanceHTTP403MarksCredentialInvalid(t *testing.T) {
 	require.True(t, snapshot.CredentialInvalid)
 }
 
+// 余额告警口径与账号停调（CNProviderBalanceCheckService.checkOne）一致：
+// 上游标记不可用或全部币种低于阈值 → BalanceLow → degraded；任一币种达标即健康。
+func TestQuotaFetcher_CNBalanceLowMarksDegraded(t *testing.T) {
+	cases := []struct {
+		name        string
+		accountID   int64
+		result      *CNProviderBalanceResult
+		balanceLow  bool
+		wantStatus  string
+		wantMessage string
+	}{
+		{
+			// 审查例：余额 5/阈值 10 的账号调度器已停调，监控不能仍绿灯。
+			name:       "balance below threshold",
+			accountID:  21,
+			result:     &CNProviderBalanceResult{Success: true, Available: true, Balance: 5, Currency: "CNY"},
+			balanceLow: true,
+			wantStatus: MonitorStatusDegraded, wantMessage: "balance low: 5 CNY",
+		},
+		{
+			name:       "upstream marked unavailable",
+			accountID:  22,
+			result:     &CNProviderBalanceResult{Success: true, Available: false, Balance: 20, Currency: "CNY"},
+			balanceLow: true,
+			wantStatus: MonitorStatusDegraded, wantMessage: "balance low: 20 CNY",
+		},
+		{
+			// deepseek 双币种：任一币种（USD 20）达标即健康。
+			name:      "any currency above threshold is healthy",
+			accountID: 23,
+			result: &CNProviderBalanceResult{
+				Success: true, Available: true, Balance: 5, Currency: "CNY",
+				Balances: []CNProviderBalanceEntry{{Currency: "CNY", Balance: 5}, {Currency: "USD", Balance: 20}},
+			},
+			wantStatus: MonitorStatusOperational,
+		},
+		{
+			name:       "single currency above threshold",
+			accountID:  24,
+			result:     &CNProviderBalanceResult{Success: true, Available: true, Balance: 20, Currency: "CNY"},
+			wantStatus: MonitorStatusOperational,
+		},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			fetcher, _, _, cnBalance, accounts := newQuotaFetcherTestSetup(t)
+			fetcher.balanceThreshold = 10
+			accounts.accounts[tc.accountID] = &Account{
+				ID:          tc.accountID,
+				Platform:    domain.PlatformKimi,
+				Credentials: map[string]any{"account_mode": AccountModePayG},
+			}
+			cnBalance.result = tc.result
+
+			snapshot := fetcher.Fetch(context.Background(), tc.accountID)
+
+			require.True(t, snapshot.Success)
+			require.Equal(t, tc.balanceLow, snapshot.BalanceLow)
+			res := deriveQuotaCheckResult(snapshot, "quota", time.Now())
+			require.Equal(t, tc.wantStatus, res.Status)
+			if tc.wantMessage != "" {
+				require.Contains(t, res.Message, tc.wantMessage)
+			} else {
+				require.Empty(t, res.Message)
+			}
+		})
+	}
+}
+
+func TestNewChannelMonitorQuotaFetcher_ThresholdFromConfig(t *testing.T) {
+	require.InDelta(t, 0.5, NewChannelMonitorQuotaFetcher(nil, nil, nil, nil, nil).balanceThreshold, 0.0001)
+
+	cfg10 := &config.Config{Gateway: config.GatewayConfig{CNProviders: config.GatewayCNProvidersConfig{BalanceThreshold: 10}}}
+	require.InDelta(t, 10, NewChannelMonitorQuotaFetcher(nil, nil, nil, nil, cfg10).balanceThreshold, 0.0001)
+
+	// 非正值（含显式 0）回退默认，避免 0 阈值下「余额=0 也不告警」。
+	cfg0 := &config.Config{Gateway: config.GatewayConfig{CNProviders: config.GatewayCNProvidersConfig{BalanceThreshold: 0}}}
+	require.InDelta(t, 0.5, NewChannelMonitorQuotaFetcher(nil, nil, nil, nil, cfg0).balanceThreshold, 0.0001)
+}
+
 func TestQuotaFetcher_NilDependenciesProduceErrorSnapshots(t *testing.T) {
 	// fetcher 本体为 nil：直接降级为错误快照，不 panic。
 	var nilFetcher *ChannelMonitorQuotaFetcher
@@ -495,10 +603,10 @@ func TestDeriveQuotaCheckResult_StatusMatrix(t *testing.T) {
 	require.Contains(t, res.Message, "95.0%")
 
 	balance := -0.5
-	depleted := &domain.MonitorQuotaSnapshot{Success: true, Balance: &balance, Currency: "CNY"}
-	res = deriveQuotaCheckResult(depleted, "quota", now)
+	lowBalance := &domain.MonitorQuotaSnapshot{Success: true, BalanceLow: true, Balance: &balance, Currency: "CNY"}
+	res = deriveQuotaCheckResult(lowBalance, "quota", now)
 	require.Equal(t, MonitorStatusDegraded, res.Status)
-	require.Contains(t, res.Message, "balance depleted")
+	require.Contains(t, res.Message, "balance low")
 
 	invalid := &domain.MonitorQuotaSnapshot{Success: false, CredentialInvalid: true, Error: "401 unauthorized"}
 	res = deriveQuotaCheckResult(invalid, "quota", now)