fix: 未登记的 Grok 文本模型回退 grok-4.5 价卡

新文本 ID 在闭集价卡上 fail-closed，请求成功而用量记 0。

- grok / grok-N* / build / composer 未登记别名继承 4.5 价
- imagine/voice/web-search/speech 等非文本族不回退

backend/internal/service/billing_service.go

@@ -10,6 +10,7 @@ import (
 	"time"
 
 	"github.com/Wei-Shaw/sub2api/internal/config"
+	"github.com/Wei-Shaw/sub2api/internal/pkg/xai"
 )
 
 // APIKeyRateLimitCacheData holds rate limit usage data cached in Redis.
@@ -843,9 +844,39 @@ func (s *BillingService) getFallbackPricing(model string) *ModelPricing {
 		return s.fallbackPrices["grok-build-0.1"]
 	}
 
+	// Unknown Grok text IDs (grok-5, dated snapshots, provider-prefixed) inherit
+	// the current default text card so a new model cannot ship unbilled.
+	if pricing := s.grokUnknownTextFamilyFallback(modelLower); pricing != nil {
+		return pricing
+	}
+
 	return nil
 }
 
+func (s *BillingService) grokUnknownTextFamilyFallback(model string) *ModelPricing {
+	if s == nil || !isGrokUnknownTextFamilyModel(model) {
+		return nil
+	}
+	return s.fallbackPrices["grok-4.5"]
+}
+
+func isGrokUnknownTextFamilyModel(model string) bool {
+	native := strings.ToLower(strings.TrimSpace(xai.StripGrokProviderPrefix(model)))
+	switch {
+	case native == "grok", native == "grok-latest":
+		return true
+	case strings.HasPrefix(native, "grok-build"),
+		strings.HasPrefix(native, "grok-composer"),
+		strings.HasPrefix(native, "composer-"):
+		return true
+	case len(native) > 5 && strings.HasPrefix(native, "grok-"):
+		rest := native[len("grok-"):]
+		return rest[0] >= '0' && rest[0] <= '9'
+	default:
+		return false
+	}
+}
+
 // HasIdentifiedTokenPricing 判断模型能否在价格表中被"确定性识别"出 token 价格。
 //
 // 与 GetModelPricing 的关键区别：本函数拒绝按子串猜系列的兜底。GetModelPricing 会

backend/internal/service/billing_service_test.go

@@ -1185,6 +1185,61 @@ func TestGetModelPricing_Grok46OfficialFallback(t *testing.T) {
 	}
 }
 
+func TestCalculateCostUnified_GroupLongContextToggleUsesPresetLadder(t *testing.T) {
+	svc := newTestBillingService()
+	resolver := NewModelPricingResolver(nil, svc)
+	tokens := UsageTokens{InputTokens: 250000, OutputTokens: 1000}
+
+	off := &Group{LongContextPricingEnabled: false}
+	disabled, err := svc.CalculateCostUnified(CostInput{
+		Model: "grok-4.5", Group: off, Tokens: tokens, RateMultiplier: 1, Resolver: resolver,
+	})
+	require.NoError(t, err)
+
+	on := &Group{LongContextPricingEnabled: true}
+	enabled, err := svc.CalculateCostUnified(CostInput{
+		Model: "grok-4.5", Group: on, Tokens: tokens, RateMultiplier: 1, Resolver: resolver,
+	})
+	require.NoError(t, err)
+
+	require.False(t, disabled.LongContextBillingApplied)
+	require.True(t, enabled.LongContextBillingApplied)
+	require.InDelta(t, disabled.InputCost*2, enabled.InputCost, 1e-12)
+	require.InDelta(t, disabled.OutputCost*2, enabled.OutputCost, 1e-12)
+}
+
+func TestGetModelPricing_UnknownGrokTextFallsBackToGrok45(t *testing.T) {
+	svc := newTestBillingService()
+	baseline, err := svc.GetModelPricing("grok-4.5")
+	require.NoError(t, err)
+
+	for _, model := range []string{"grok-5", "grok-5-latest", "x-ai/grok-7", "grok-4.7-beta"} {
+		pricing, err := svc.GetModelPricing(model)
+		require.NoError(t, err, "model %s", model)
+		require.InDelta(t, baseline.InputPricePerToken, pricing.InputPricePerToken, 1e-12, model)
+		require.InDelta(t, baseline.OutputPricePerToken, pricing.OutputPricePerToken, 1e-12, model)
+		require.InDelta(t, baseline.CacheReadPricePerToken, pricing.CacheReadPricePerToken, 1e-12, model)
+	}
+
+	for _, model := range []string{
+		"grok-imagine-image-3.0",
+		"grok-imagine-video-2",
+		"grok-voice-latest",
+		"grok-web-search",
+		"grok-x-search",
+		"grok-speech-1",
+	} {
+		_, err := svc.GetModelPricing(model)
+		require.Error(t, err, "non-text grok family %s must not inherit grok-4.5 token rates", model)
+		require.ErrorIs(t, err, ErrModelPricingUnavailable)
+	}
+
+	// Known cards stay on their own rate, not the 4.5 family floor.
+	build, err := svc.GetModelPricing("grok-build-0.1")
+	require.NoError(t, err)
+	require.InDelta(t, 1e-6, build.InputPricePerToken, 1e-12)
+}
+
 func TestGetModelPricing_GrokCatalogFallbacks(t *testing.T) {
 	svc := newTestBillingService()