refactor: remove Anthropic digest chain from Messages handler

The digest chain fallback is only needed for Gemini endpoints, not
for the Anthropic Messages API path. Remove the handler integration
while keeping the reusable service/repository layer for future use.

backend/internal/handler/gateway_handler.go

@@ -22,7 +22,6 @@ import (
 	"github.com/Wei-Shaw/sub2api/internal/service"
 
 	"github.com/gin-gonic/gin"
-	"github.com/google/uuid"
 )
 
 // GatewayHandler handles API gateway requests
@@ -213,53 +212,6 @@ func (h *GatewayHandler) Messages(c *gin.Context) {
 	if sessionKey != "" {
 		sessionBoundAccountID, _ = h.gatewayService.GetCachedSessionAccountID(c.Request.Context(), apiKey.GroupID, sessionKey)
 	}
-
-	// === Anthropic 内容摘要会话 Fallback 逻辑 ===
-	// 当原有会话标识无效时（sessionBoundAccountID == 0），尝试基于内容摘要链匹配
-	var anthropicDigestChain string
-	var anthropicPrefixHash string
-	var anthropicSessionUUID string
-	useAnthropicDigestFallback := sessionBoundAccountID == 0 && platform != service.PlatformGemini
-
-	if useAnthropicDigestFallback {
-		anthropicDigestChain = service.BuildAnthropicDigestChain(parsedReq)
-		if anthropicDigestChain != "" {
-			userAgent := c.GetHeader("User-Agent")
-			clientIP := ip.GetClientIP(c)
-			anthropicPrefixHash = service.GenerateGeminiPrefixHash(
-				subject.UserID,
-				apiKey.ID,
-				clientIP,
-				userAgent,
-				platform,
-				reqModel,
-			)
-
-			foundUUID, foundAccountID, found := h.gatewayService.FindAnthropicSession(
-				c.Request.Context(),
-				derefGroupID(apiKey.GroupID),
-				anthropicPrefixHash,
-				anthropicDigestChain,
-			)
-			if found {
-				sessionBoundAccountID = foundAccountID
-				anthropicSessionUUID = foundUUID
-				log.Printf("[Anthropic] Digest fallback matched: uuid=%s, accountID=%d, chain=%s",
-					foundUUID[:8], foundAccountID, truncateDigestChain(anthropicDigestChain))
-
-				if sessionKey == "" {
-					sessionKey = service.GenerateAnthropicDigestSessionKey(anthropicPrefixHash, foundUUID)
-				}
-				_ = h.gatewayService.BindStickySession(c.Request.Context(), apiKey.GroupID, sessionKey, foundAccountID)
-			} else {
-				anthropicSessionUUID = uuid.New().String()
-				if sessionKey == "" {
-					sessionKey = service.GenerateAnthropicDigestSessionKey(anthropicPrefixHash, anthropicSessionUUID)
-				}
-			}
-		}
-	}
-
 	// 判断是否真的绑定了粘性会话：有 sessionKey 且已经绑定到某个账号
 	hasBoundSession := sessionKey != "" && sessionBoundAccountID > 0
 
@@ -588,20 +540,6 @@ func (h *GatewayHandler) Messages(c *gin.Context) {
 			userAgent := c.GetHeader("User-Agent")
 			clientIP := ip.GetClientIP(c)
 
-			// 保存 Anthropic 内容摘要会话（用于 Fallback 匹配）
-			if useAnthropicDigestFallback && anthropicDigestChain != "" && anthropicPrefixHash != "" {
-				if err := h.gatewayService.SaveAnthropicSession(
-					c.Request.Context(),
-					derefGroupID(apiKey.GroupID),
-					anthropicPrefixHash,
-					anthropicDigestChain,
-					anthropicSessionUUID,
-					account.ID,
-				); err != nil {
-					log.Printf("[Anthropic] Failed to save digest session: %v", err)
-				}
-			}
-
 			// 异步记录使用量（subscription已在函数开头获取）
 			go func(result *service.ForwardResult, usedAccount *service.Account, ua, clientIP string, fcb bool) {
 				ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)