fix: 添加混合渠道警告确认框和过滤 prompt_cache_retention 参数

- 前端: EditAccountModal 和 CreateAccountModal 添加 409 mixed_channel_warning 处理
- 前端: 弹出确认框让用户确认混合渠道风险
- 后端: 过滤 OpenAI 请求中的 prompt_cache_retention 参数（上游不支持）
- 添加中英文翻译
Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>

backend/internal/service/openai_gateway_service.go

@@ -649,6 +649,12 @@ func (s *OpenAIGatewayService) Forward(ctx context.Context, c *gin.Context, acco
 				bodyModified = true
 			}
 		}
+
+		// Remove prompt_cache_retention (not supported by upstream OpenAI API)
+		if _, has := reqBody["prompt_cache_retention"]; has {
+			delete(reqBody, "prompt_cache_retention")
+			bodyModified = true
+		}
 	}
 
 	// Re-serialize body only if modified

frontend/src/components/account/CreateAccountModal.vue

@@ -2157,6 +2157,46 @@ const handleClose = () => {
   emit('close')
 }
 
+// Helper function to create account with mixed channel warning handling
+const doCreateAccount = async (payload: any, confirmMixedChannelRisk = false) => {
+  if (confirmMixedChannelRisk) {
+    payload.confirm_mixed_channel_risk = true
+  }
+  
+  submitting.value = true
+  try {
+    await adminAPI.accounts.create(payload)
+    appStore.showSuccess(t('admin.accounts.accountCreated'))
+    emit('created')
+    handleClose()
+  } catch (error: any) {
+    // Handle 409 mixed_channel_warning - show confirmation dialog
+    if (error.response?.status === 409 && error.response?.data?.error === 'mixed_channel_warning') {
+      const details = error.response.data.details || {}
+      const groupName = details.group_name || 'Unknown'
+      const currentPlatform = details.current_platform || 'Unknown'
+      const otherPlatform = details.other_platform || 'Unknown'
+      
+      const confirmMessage = t('admin.accounts.mixedChannelWarning', {
+        groupName,
+        currentPlatform,
+        otherPlatform
+      })
+      
+      if (confirm(confirmMessage)) {
+        // Retry with confirmation flag
+        submitting.value = false
+        await doCreateAccount(payload, true)
+        return
+      }
+    } else {
+      appStore.showError(error.response?.data?.detail || t('admin.accounts.failedToCreate'))
+    }
+  } finally {
+    submitting.value = false
+  }
+}
+
 const handleSubmit = async () => {
   // For OAuth-based type, handle OAuth flow (goes to step 2)
   if (isOAuthFlow.value) {
@@ -2213,21 +2253,11 @@ const handleSubmit = async () => {
 
   form.credentials = credentials
 
-  submitting.value = true
-  try {
-    await adminAPI.accounts.create({
+  await doCreateAccount({
     ...form,
     group_ids: form.group_ids,
     auto_pause_on_expired: autoPauseOnExpired.value
   })
-    appStore.showSuccess(t('admin.accounts.accountCreated'))
-    emit('created')
-    handleClose()
-  } catch (error: any) {
-    appStore.showError(error.response?.data?.detail || t('admin.accounts.failedToCreate'))
-  } finally {
-    submitting.value = false
-  }
 }
 
 const goBackToBasicInfo = () => {

frontend/src/components/account/EditAccountModal.vue

@@ -8,7 +8,7 @@
     <form
       v-if="account"
       id="edit-account-form"
-      @submit.prevent="handleSubmit"
+      @submit.prevent="() => handleSubmit()"
       class="space-y-5"
     >
       <div>
@@ -1294,12 +1294,17 @@ const handleClose = () => {
   emit('close')
 }
 
-const handleSubmit = async () => {
+const handleSubmit = async (confirmMixedChannelRisk = false) => {
   if (!props.account) return
 
   submitting.value = true
   try {
     const updatePayload: Record<string, unknown> = { ...form }
+    
+    // Add confirmation flag if user confirmed mixed channel risk
+    if (confirmMixedChannelRisk) {
+      updatePayload.confirm_mixed_channel_risk = true
+    }
     // 后端期望 proxy_id: 0 表示清除代理，而不是 null
     if (updatePayload.proxy_id === null) {
       updatePayload.proxy_id = 0
@@ -1415,7 +1420,28 @@ const handleSubmit = async () => {
     emit('updated')
     handleClose()
   } catch (error: any) {
+    // Handle 409 mixed_channel_warning - show confirmation dialog
+    if (error.response?.status === 409 && error.response?.data?.error === 'mixed_channel_warning') {
+      const details = error.response.data.details || {}
+      const groupName = details.group_name || 'Unknown'
+      const currentPlatform = details.current_platform || 'Unknown'
+      const otherPlatform = details.other_platform || 'Unknown'
+      
+      const confirmMessage = t('admin.accounts.mixedChannelWarning', {
+        groupName,
+        currentPlatform,
+        otherPlatform
+      })
+      
+      if (confirm(confirmMessage)) {
+        // Retry with confirmation flag
+        submitting.value = false
+        await handleSubmit(true)
+        return
+      }
+    } else {
       appStore.showError(error.response?.data?.message || error.response?.data?.detail || t('admin.accounts.failedToUpdate'))
+    }
   } finally {
     submitting.value = false
   }

frontend/src/i18n/locales/en.ts

@@ -1306,6 +1306,7 @@ export default {
       accountUpdated: 'Account updated successfully',
       failedToCreate: 'Failed to create account',
       failedToUpdate: 'Failed to update account',
+      mixedChannelWarning: 'Warning: Group "{groupName}" contains both {currentPlatform} and {otherPlatform} accounts. Mixing different channels may cause thinking block signature validation issues, which will fallback to non-thinking mode. Are you sure you want to continue?',
       pleaseEnterAccountName: 'Please enter account name',
       pleaseEnterApiKey: 'Please enter API Key',
       apiKeyIsRequired: 'API Key is required',

frontend/src/i18n/locales/zh.ts

@@ -1439,6 +1439,7 @@ export default {
       accountUpdated: '账号更新成功',
       failedToCreate: '创建账号失败',
       failedToUpdate: '更新账号失败',
+      mixedChannelWarning: '警告：分组 "{groupName}" 中同时包含 {currentPlatform} 和 {otherPlatform} 账号。混合使用不同渠道可能导致 thinking block 签名验证问题，会自动回退到非 thinking 模式。确定要继续吗？',
       pleaseEnterAccountName: '请输入账号名称',
       pleaseEnterApiKey: '请输入 API Key',
       apiKeyIsRequired: 'API Key 是必需的',