diff --git a/backend/internal/handler/openai_gateway_handler.go b/backend/internal/handler/openai_gateway_handler.go
index 951c263dd4..6730529743 100644
--- a/backend/internal/handler/openai_gateway_handler.go
+++ b/backend/internal/handler/openai_gateway_handler.go
@@ -1493,6 +1493,18 @@ func (h *OpenAIGatewayHandler) ResponsesWebSocket(c *gin.Context) {
 		if channelMappingWS.Mapped {
 			wsFirstMessage = h.gatewayService.ReplaceModelInBody(firstMessage, channelMappingWS.MappedModel)
 		}
+		// 切组/会话失配防护：previous_response_id 未在当前分组命中粘连账号（StickyPreviousHit=false），
+		// 说明该会话链不属于本次调度到的账号，原样转发会触发上游会话链鉴权失败（“鉴权失败，请检查 API Key”）。
+		// 故剥离首包里的 previous_response_id，改用首包内 input 重建上下文；带 function_call_output 的
+		// 工具续链无法重建，保持原样。仅作用于首轮首包，后续 turn 的续链由 WS 转发层既有逻辑处理。
+		if previousResponseID != "" && !scheduleDecision.StickyPreviousHit &&
+			!service.ValidateFunctionCallOutputContextBytes(wsFirstMessage).HasFunctionCallOutput {
+			wsFirstMessage = service.RemovePreviousResponseIDFromBody(wsFirstMessage)
+			reqLog.Debug("openai.websocket_previous_response_id_stripped_cross_group",
+				zap.Int64("account_id", account.ID),
+				zap.String("schedule_layer", scheduleDecision.Layer),
+			)
+		}
 
 		// WebSocket 首包可能很大，hash 必须在 hooks 外算成字符串，避免 AfterTurn 闭包保活请求体。
 		requestPayloadHash = service.HashUsageRequestPayload(wsFirstMessage)
diff --git a/backend/internal/service/channel_service.go b/backend/internal/service/channel_service.go
index 4bf0147f38..18bd4d5324 100644
--- a/backend/internal/service/channel_service.go
+++ b/backend/internal/service/channel_service.go
@@ -572,6 +572,21 @@ func ReplaceModelInBody(body []byte, newModel string) []byte {
 	return newBody
 }
 
+// RemovePreviousResponseIDFromBody 删除请求体中的 previous_response_id，用于会话失配时改用完整 input 重建上下文。
+func RemovePreviousResponseIDFromBody(body []byte) []byte {
+	if len(body) == 0 {
+		return body
+	}
+	if !gjson.GetBytes(body, "previous_response_id").Exists() {
+		return body
+	}
+	newBody, err := sjson.DeleteBytes(body, "previous_response_id")
+	if err != nil {
+		return body
+	}
+	return newBody
+}
+
 // validateChannelConfig 校验渠道的定价和映射配置（冲突检测 + 区间校验 + 计费模式校验）。
 // Create 和 Update 共用此函数，避免重复。
 func validateChannelConfig(pricing []ChannelModelPricing, mapping map[string]map[string]string) error {
diff --git a/backend/internal/service/channel_service_test.go b/backend/internal/service/channel_service_test.go
index e737a21125..381b8c6c25 100644
--- a/backend/internal/service/channel_service_test.go
+++ b/backend/internal/service/channel_service_test.go
@@ -9,6 +9,7 @@ import (
 
 	"github.com/Wei-Shaw/sub2api/internal/pkg/pagination"
 	"github.com/stretchr/testify/require"
+	"github.com/tidwall/gjson"
 )
 
 // ---------------------------------------------------------------------------
@@ -1921,6 +1922,33 @@ func TestReplaceModelInBody_InvalidJSON(t *testing.T) {
 	require.Equal(t, arrayBody, result2)
 }
 
+func TestRemovePreviousResponseIDFromBody(t *testing.T) {
+	t.Run("empty body returned as-is", func(t *testing.T) {
+		require.Equal(t, []byte{}, RemovePreviousResponseIDFromBody([]byte{}))
+		require.Nil(t, RemovePreviousResponseIDFromBody(nil))
+	})
+
+	t.Run("no previous_response_id field is a no-op", func(t *testing.T) {
+		body := []byte(`{"model":"gpt-5","input":"hi"}`)
+		result := RemovePreviousResponseIDFromBody(body)
+		require.Equal(t, body, result)
+	})
+
+	t.Run("strips previous_response_id and preserves other fields", func(t *testing.T) {
+		body := []byte(`{"model":"gpt-5","previous_response_id":"resp_abc","input":"hi"}`)
+		result := RemovePreviousResponseIDFromBody(body)
+		require.False(t, gjson.GetBytes(result, "previous_response_id").Exists())
+		require.Equal(t, "gpt-5", gjson.GetBytes(result, "model").String())
+		require.Equal(t, "hi", gjson.GetBytes(result, "input").String())
+	})
+
+	t.Run("empty-string previous_response_id is also stripped", func(t *testing.T) {
+		body := []byte(`{"model":"gpt-5","previous_response_id":""}`)
+		result := RemovePreviousResponseIDFromBody(body)
+		require.False(t, gjson.GetBytes(result, "previous_response_id").Exists())
+	})
+}
+
 // ===========================================================================
 // 7. isPlatformPricingMatch
 // ===========================================================================
diff --git a/backend/internal/service/openai_ws_state_store.go b/backend/internal/service/openai_ws_state_store.go
index b606baa1a3..d3b6891b0a 100644
--- a/backend/internal/service/openai_ws_state_store.go
+++ b/backend/internal/service/openai_ws_state_store.go
@@ -100,9 +100,10 @@ func (s *defaultOpenAIWSStateStore) BindResponseAccount(ctx context.Context, gro
 	s.maybeCleanup()
 
 	expiresAt := time.Now().Add(ttl)
+	mapKey := openAIWSResponseAccountMapKey(groupID, id)
 	s.responseToAccountMu.Lock()
-	ensureBindingCapacity(s.responseToAccount, id, openAIWSStateStoreMaxEntriesPerMap)
-	s.responseToAccount[id] = openAIWSAccountBinding{accountID: accountID, expiresAt: expiresAt}
+	ensureBindingCapacity(s.responseToAccount, mapKey, openAIWSStateStoreMaxEntriesPerMap)
+	s.responseToAccount[mapKey] = openAIWSAccountBinding{accountID: accountID, expiresAt: expiresAt}
 	s.responseToAccountMu.Unlock()
 
 	if s.cache == nil {
@@ -122,8 +123,9 @@ func (s *defaultOpenAIWSStateStore) GetResponseAccount(ctx context.Context, grou
 	s.maybeCleanup()
 
 	now := time.Now()
+	mapKey := openAIWSResponseAccountMapKey(groupID, id)
 	s.responseToAccountMu.RLock()
-	if binding, ok := s.responseToAccount[id]; ok {
+	if binding, ok := s.responseToAccount[mapKey]; ok {
 		if now.Before(binding.expiresAt) {
 			accountID := binding.accountID
 			s.responseToAccountMu.RUnlock()
@@ -153,7 +155,7 @@ func (s *defaultOpenAIWSStateStore) DeleteResponseAccount(ctx context.Context, g
 		return nil
 	}
 	s.responseToAccountMu.Lock()
-	delete(s.responseToAccount, id)
+	delete(s.responseToAccount, openAIWSResponseAccountMapKey(groupID, id))
 	s.responseToAccountMu.Unlock()
 
 	if s.cache == nil {
@@ -417,6 +419,11 @@ func openAIWSResponseAccountCacheKey(responseID string) string {
 	return openAIWSResponseAccountCachePrefix + hex.EncodeToString(sum[:])
 }
 
+// openAIWSResponseAccountMapKey 本地热缓存按分组隔离的 key，与 Redis 层保持一致，避免跨组命中。
+func openAIWSResponseAccountMapKey(groupID int64, responseID string) string {
+	return fmt.Sprintf("%d:%s", groupID, responseID)
+}
+
 func normalizeOpenAIWSTTL(ttl time.Duration) time.Duration {
 	if ttl <= 0 {
 		return time.Hour