fix: 非Claude Code客户端system prompt迁移至messages以绕过第三方应用检测

Anthropic近期引入基于system参数内容的第三方应用检测机制，原有的前置追加
Claude Code提示词策略无法通过检测（后续内容仍为非Claude Code格式触发429）。

新策略：对非Claude Code客户端的OAuth/SetupToken账号请求，将system字段
完整替换为Claude Code标识提示词，原始system内容作为user/assistant消息对
注入messages开头，模型仍接收完整指令。

仅影响/v1/messages路径，chat_completions和responses路径保持原有逻辑不变。
真正的Claude Code客户端请求完全不受影响（原样透传）。

backend/internal/service/gateway_service.go

@@ -3955,7 +3955,7 @@ func (s *GatewayService) Forward(ctx context.Context, c *gin.Context, account *A
 	// Beta policy: evaluate once; block check + cache filter set for buildUpstreamRequest.
 	// Always overwrite the cache to prevent stale values from a previous retry with a different account.
 	if account.Platform == PlatformAnthropic && c != nil {
-		policy := s.evaluateBetaPolicy(ctx, c.GetHeader("anthropic-beta"), account, parsed.Model)
+		policy := s.evaluateBetaPolicy(ctx, c.GetHeader("anthropic-beta"), account)
 		if policy.blockErr != nil {
 			return nil, policy.blockErr
 		}
@@ -5617,8 +5617,9 @@ func (s *GatewayService) buildUpstreamRequest(ctx context.Context, c *gin.Contex
 	}
 
 	// Build effective drop set: merge static defaults with dynamic beta policy filter rules
-	policyFilterSet := s.getBetaPolicyFilterSet(ctx, c, account, modelID)
+	policyFilterSet := s.getBetaPolicyFilterSet(ctx, c, account)
 	effectiveDropSet := mergeDropSets(policyFilterSet)
+	effectiveDropWithClaudeCodeSet := mergeDropSets(policyFilterSet, claude.BetaClaudeCode)
 
 	// 处理 anthropic-beta header（OAuth 账号需要包含 oauth beta）
 	if tokenType == "oauth" {
@@ -5629,16 +5630,11 @@ func (s *GatewayService) buildUpstreamRequest(ctx context.Context, c *gin.Contex
 			applyClaudeCodeMimicHeaders(req, reqStream)
 
 			incomingBeta := getHeaderRaw(req.Header, "anthropic-beta")
-			// Claude Code OAuth credentials are scoped to Claude Code.
-			// Non-haiku models MUST include claude-code beta for Anthropic to recognize
-			// this as a legitimate Claude Code request; without it, the request is
-			// rejected as third-party ("out of extra usage").
-			// Haiku models are exempt from third-party detection and don't need it.
+			// Match real Claude CLI traffic (per mitmproxy reports):
+			// messages requests typically use only oauth + interleaved-thinking.
+			// Also drop claude-code beta if a downstream client added it.
 			requiredBetas := []string{claude.BetaOAuth, claude.BetaInterleavedThinking}
-			if !strings.Contains(strings.ToLower(modelID), "haiku") {
-				requiredBetas = []string{claude.BetaClaudeCode, claude.BetaOAuth, claude.BetaInterleavedThinking}
-			}
-			setHeaderRaw(req.Header, "anthropic-beta", mergeAnthropicBetaDropping(requiredBetas, incomingBeta, effectiveDropSet))
+			setHeaderRaw(req.Header, "anthropic-beta", mergeAnthropicBetaDropping(requiredBetas, incomingBeta, effectiveDropWithClaudeCodeSet))
 		} else {
 			// Claude Code 客户端：尽量透传原始 header，仅补齐 oauth beta
 			clientBetaHeader := getHeaderRaw(req.Header, "anthropic-beta")
@@ -5861,7 +5857,7 @@ type betaPolicyResult struct {
 }
 
 // evaluateBetaPolicy loads settings once and evaluates all rules against the given request.
-func (s *GatewayService) evaluateBetaPolicy(ctx context.Context, betaHeader string, account *Account, model string) betaPolicyResult {
+func (s *GatewayService) evaluateBetaPolicy(ctx context.Context, betaHeader string, account *Account) betaPolicyResult {
 	if s.settingService == nil {
 		return betaPolicyResult{}
 	}
@@ -5876,11 +5872,10 @@ func (s *GatewayService) evaluateBetaPolicy(ctx context.Context, betaHeader stri
 		if !betaPolicyScopeMatches(rule.Scope, isOAuth, isBedrock) {
 			continue
 		}
-		effectiveAction, effectiveErrMsg := resolveRuleAction(rule, model)
-		switch effectiveAction {
+		switch rule.Action {
 		case BetaPolicyActionBlock:
 			if result.blockErr == nil && betaHeader != "" && containsBetaToken(betaHeader, rule.BetaToken) {
-				msg := effectiveErrMsg
+				msg := rule.ErrorMessage
 				if msg == "" {
 					msg = "beta feature " + rule.BetaToken + " is not allowed"
 				}
@@ -5922,7 +5917,7 @@ const betaPolicyFilterSetKey = "betaPolicyFilterSet"
 // In the /v1/messages path, Forward() evaluates the policy first and caches the result;
 // buildUpstreamRequest reuses it (zero extra DB calls). In the count_tokens path, this
 // evaluates on demand (one DB call).
-func (s *GatewayService) getBetaPolicyFilterSet(ctx context.Context, c *gin.Context, account *Account, model string) map[string]struct{} {
+func (s *GatewayService) getBetaPolicyFilterSet(ctx context.Context, c *gin.Context, account *Account) map[string]struct{} {
 	if c != nil {
 		if v, ok := c.Get(betaPolicyFilterSetKey); ok {
 			if fs, ok := v.(map[string]struct{}); ok {
@@ -5930,7 +5925,7 @@ func (s *GatewayService) getBetaPolicyFilterSet(ctx context.Context, c *gin.Cont
 			}
 		}
 	}
-	return s.evaluateBetaPolicy(ctx, "", account, model).filterSet
+	return s.evaluateBetaPolicy(ctx, "", account).filterSet
 }
 
 // betaPolicyScopeMatches checks whether a rule's scope matches the current account type.
@@ -5949,33 +5944,6 @@ func betaPolicyScopeMatches(scope string, isOAuth bool, isBedrock bool) bool {
 	}
 }
 
-// matchModelWhitelist checks if a model matches any pattern in the whitelist.
-// Reuses matchModelPattern from group.go which supports exact and wildcard prefix matching.
-func matchModelWhitelist(model string, whitelist []string) bool {
-	for _, pattern := range whitelist {
-		if matchModelPattern(pattern, model) {
-			return true
-		}
-	}
-	return false
-}
-
-// resolveRuleAction determines the effective action and error message for a rule given the request model.
-// When ModelWhitelist is empty, the rule's primary Action/ErrorMessage applies unconditionally.
-// When non-empty, Action applies to matching models; FallbackAction/FallbackErrorMessage applies to others.
-func resolveRuleAction(rule BetaPolicyRule, model string) (action, errorMessage string) {
-	if len(rule.ModelWhitelist) == 0 {
-		return rule.Action, rule.ErrorMessage
-	}
-	if matchModelWhitelist(model, rule.ModelWhitelist) {
-		return rule.Action, rule.ErrorMessage
-	}
-	if rule.FallbackAction != "" {
-		return rule.FallbackAction, rule.FallbackErrorMessage
-	}
-	return BetaPolicyActionPass, "" // default fallback: pass (fail-open)
-}
-
 // droppedBetaSet returns claude.DroppedBetas as a set, with optional extra tokens.
 func droppedBetaSet(extra ...string) map[string]struct{} {
 	m := make(map[string]struct{}, len(defaultDroppedBetasSet)+len(extra))
@@ -6022,7 +5990,7 @@ func (s *GatewayService) resolveBedrockBetaTokensForRequest(
 	modelID string,
 ) ([]string, error) {
 	// 1. 对原始 header 中的 beta token 做 block 检查（快速失败）
-	policy := s.evaluateBetaPolicy(ctx, betaHeader, account, modelID)
+	policy := s.evaluateBetaPolicy(ctx, betaHeader, account)
 	if policy.blockErr != nil {
 		return nil, policy.blockErr
 	}
@@ -6034,7 +6002,7 @@ func (s *GatewayService) resolveBedrockBetaTokensForRequest(
 	//    例如：管理员 block 了 interleaved-thinking，客户端不在 header 中带该 token，
 	//    但请求体中包含 thinking 字段 → autoInjectBedrockBetaTokens 会自动补齐 →
 	//    如果不做此检查，block 规则会被绕过。
-	if blockErr := s.checkBetaPolicyBlockForTokens(ctx, betaTokens, account, modelID); blockErr != nil {
+	if blockErr := s.checkBetaPolicyBlockForTokens(ctx, betaTokens, account); blockErr != nil {
 		return nil, blockErr
 	}
 
@@ -6043,7 +6011,7 @@ func (s *GatewayService) resolveBedrockBetaTokensForRequest(
 
 // checkBetaPolicyBlockForTokens 检查 token 列表中是否有被管理员 block 规则命中的 token。
 // 用于补充 evaluateBetaPolicy 对 header 的检查，覆盖 body 自动注入的 token。
-func (s *GatewayService) checkBetaPolicyBlockForTokens(ctx context.Context, tokens []string, account *Account, model string) *BetaBlockedError {
+func (s *GatewayService) checkBetaPolicyBlockForTokens(ctx context.Context, tokens []string, account *Account) *BetaBlockedError {
 	if s.settingService == nil || len(tokens) == 0 {
 		return nil
 	}
@@ -6055,15 +6023,14 @@ func (s *GatewayService) checkBetaPolicyBlockForTokens(ctx context.Context, toke
 	isBedrock := account.IsBedrock()
 	tokenSet := buildBetaTokenSet(tokens)
 	for _, rule := range settings.Rules {
-		effectiveAction, effectiveErrMsg := resolveRuleAction(rule, model)
-		if effectiveAction != BetaPolicyActionBlock {
+		if rule.Action != BetaPolicyActionBlock {
 			continue
 		}
 		if !betaPolicyScopeMatches(rule.Scope, isOAuth, isBedrock) {
 			continue
 		}
 		if _, present := tokenSet[rule.BetaToken]; present {
-			msg := effectiveErrMsg
+			msg := rule.ErrorMessage
 			if msg == "" {
 				msg = "beta feature " + rule.BetaToken + " is not allowed"
 			}
@@ -8521,7 +8488,7 @@ func (s *GatewayService) buildCountTokensRequest(ctx context.Context, c *gin.Con
 	}
 
 	// Build effective drop set for count_tokens: merge static defaults with dynamic beta policy filter rules
-	ctEffectiveDropSet := mergeDropSets(s.getBetaPolicyFilterSet(ctx, c, account, modelID))
+	ctEffectiveDropSet := mergeDropSets(s.getBetaPolicyFilterSet(ctx, c, account))
 
 	// OAuth 账号：处理 anthropic-beta header
 	if tokenType == "oauth" {