fix: use i18n for mixed-channel warning messages and improve bulk pre-check

- BulkUpdate handler: add structured details to 409 response
- BulkUpdateAccounts: simplify to global pre-check before any DB write;
  remove per-account snapshot tracking which is no longer needed
- MixedChannelError.Error(): restore English message for API compatibility
- BulkEditAccountModal: use t() with details for both pre-check and 409
  fallback paths instead of displaying raw backend strings
- Update test to verify pre-check blocks on existing group conflicts

backend/internal/handler/admin/account_handler.go

@@ -1127,6 +1127,12 @@ func (h *AccountHandler) BulkUpdate(c *gin.Context) {
 			c.JSON(409, gin.H{
 				"error":   "mixed_channel_warning",
 				"message": mixedErr.Error(),
+				"details": gin.H{
+					"group_id":         mixedErr.GroupID,
+					"group_name":       mixedErr.GroupName,
+					"current_platform": mixedErr.CurrentPlatform,
+					"other_platform":   mixedErr.OtherPlatform,
+				},
 			})
 			return
 		}

backend/internal/service/admin_service.go

@@ -1542,27 +1542,16 @@ func (s *adminServiceImpl) BulkUpdateAccounts(ctx context.Context, input *BulkUp
 	// 预加载账号平台信息（混合渠道检查或 Sora 同步需要）。
 	platformByID := map[int64]string{}
 	groupAccountsByID := map[int64][]Account{}
-	groupNameByID := map[int64]string{}
 	if needMixedChannelCheck {
 		accounts, err := s.accountRepo.GetByIDs(ctx, input.AccountIDs)
-		if err != nil {
-			if needMixedChannelCheck {
-				return nil, err
-			}
-		} else {
-			for _, account := range accounts {
-				if account != nil {
-					platformByID[account.ID] = account.Platform
-				}
-			}
-		}
-
-		loadedAccounts, loadedNames, err := s.preloadMixedChannelRiskData(ctx, *input.GroupIDs)
 		if err != nil {
 			return nil, err
 		}
-		groupAccountsByID = loadedAccounts
-		groupNameByID = loadedNames
+		for _, account := range accounts {
+			if account != nil {
+				platformByID[account.ID] = account.Platform
+			}
+		}
 	}
 
 	// 预检查混合渠道风险：在任何写操作之前，若发现风险立即返回错误。
@@ -2529,6 +2518,6 @@ type MixedChannelError struct {
 }
 
 func (e *MixedChannelError) Error() string {
-	return fmt.Sprintf("警告：分组 \"%s\" 中同时包含 %s 和 %s 账号。混合使用不同渠道可能导致 thinking block 签名验证问题，请确保 Anthropic 账号是 Antigravity 反代暴露的 api。确定要继续吗？",
+	return fmt.Sprintf("mixed_channel_warning: Group '%s' contains both %s and %s accounts. Using mixed channels in the same context may cause thinking block signature validation issues, which will fallback to non-thinking mode for historical messages.",
 		e.GroupName, e.CurrentPlatform, e.OtherPlatform)
 }

backend/internal/service/admin_service_bulk_update_test.go

@@ -139,34 +139,34 @@ func TestAdminService_BulkUpdateAccounts_NilGroupRepoReturnsError(t *testing.T)
 	require.Contains(t, err.Error(), "group repository not configured")
 }
 
-func TestAdminService_BulkUpdateAccounts_MixedChannelCheckUsesUpdatedSnapshot(t *testing.T) {
+// TestAdminService_BulkUpdateAccounts_MixedChannelPreCheckBlocksOnExistingConflict verifies
+// that the global pre-check detects a conflict with existing group members and returns an
+// error before any DB write is performed.
+func TestAdminService_BulkUpdateAccounts_MixedChannelPreCheckBlocksOnExistingConflict(t *testing.T) {
 	repo := &accountRepoStubForBulkUpdate{
 		getByIDsAccounts: []*Account{
-			{ID: 1, Platform: PlatformAnthropic},
-			{ID: 2, Platform: PlatformAntigravity},
+			{ID: 1, Platform: PlatformAntigravity},
 		},
+		// Group 10 already contains an Anthropic account.
 		listByGroupData: map[int64][]Account{
-			10: {},
+			10: {{ID: 99, Platform: PlatformAnthropic}},
 		},
 	}
 	svc := &adminServiceImpl{
 		accountRepo: repo,
-		groupRepo:   &groupRepoStubForAdmin{getByID: &Group{ID: 10, Name: "目标分组"}},
+		groupRepo:   &groupRepoStubForAdmin{getByID: &Group{ID: 10, Name: "target-group"}},
 	}
 
 	groupIDs := []int64{10}
 	input := &BulkUpdateAccountsInput{
-		AccountIDs: []int64{1, 2},
+		AccountIDs: []int64{1},
 		GroupIDs:   &groupIDs,
 	}
 
 	result, err := svc.BulkUpdateAccounts(context.Background(), input)
-	require.NoError(t, err)
-	require.Equal(t, 1, result.Success)
-	require.Equal(t, 1, result.Failed)
-	require.ElementsMatch(t, []int64{1}, result.SuccessIDs)
-	require.ElementsMatch(t, []int64{2}, result.FailedIDs)
-	require.Len(t, result.Results, 2)
-	require.Contains(t, result.Results[1].Error, "mixed channel")
-	require.Equal(t, []int64{1}, repo.bindGroupsCalls)
+	require.Nil(t, result)
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "mixed channel")
+	// No BindGroups should have been called since the check runs before any write.
+	require.Empty(t, repo.bindGroupsCalls)
 }

frontend/src/components/account/BulkEditAccountModal.vue

@@ -1283,7 +1283,11 @@ const preCheckMixedChannelRisk = async (built: Record<string, unknown>): Promise
     if (!result.has_risk) return true
 
     pendingUpdatesForConfirm.value = built
-    mixedChannelWarningMessage.value = result.message || t('admin.accounts.bulkEdit.failed')
+    mixedChannelWarningMessage.value = t('admin.accounts.mixedChannelWarning', {
+      groupName: result.details?.group_name,
+      currentPlatform: result.details?.current_platform,
+      otherPlatform: result.details?.other_platform
+    })
     showMixedChannelWarning.value = true
     return false
   } catch (error: any) {
@@ -1358,7 +1362,11 @@ const submitBulkUpdate = async (baseUpdates: Record<string, unknown>) => {
     // 兜底：多平台混合场景下，预检查跳过，由后端 409 触发确认框
     if (error.status === 409 && error.error === 'mixed_channel_warning') {
       pendingUpdatesForConfirm.value = baseUpdates
-      mixedChannelWarningMessage.value = error.message
+      mixedChannelWarningMessage.value = t('admin.accounts.mixedChannelWarning', {
+        groupName: error.details?.group_name,
+        currentPlatform: error.details?.current_platform,
+        otherPlatform: error.details?.other_platform
+      })
       showMixedChannelWarning.value = true
     } else {
       appStore.showError(error.message || t('admin.accounts.bulkEdit.failed'))