feat(gateway): harden failover and payload handling

Retry pre-response transport failures across candidates with an explicit stop policy, and propagate end-to-end timing into usage records and UI diagnostics.

Remove legacy body, import, cookie, PII, and tunnel replay caps while preserving optional operator-configured gateway limits.

frontend/src/api/dashboard.ts

@@ -266,6 +266,8 @@ export interface RequestDetail {
   scheduling_failure?: RequestSchedulingFailure | null
   response_time_ms: number
   first_byte_time_ms?: number | null
+  end_to_end_time_ms?: number | null
+  end_to_end_first_byte_time_ms?: number | null
   created_at: string
   updated_at?: string | null
   request_headers?: Record<string, unknown>

frontend/src/api/endpoints/types/provider.ts

@@ -846,6 +846,7 @@ export interface FailoverRuleItem {
 
 export interface FailoverRulesConfig {
   max_retries?: number
+  stop_on_transport_errors?: boolean
   stop_status_codes?: number[]
   stop_on_status_codes?: number[]
   early_stop_status_codes?: number[]

frontend/src/api/me.ts

@@ -68,6 +68,8 @@ export interface UsageRecordDetail {
   rate_multiplier?: number  // 成本倍率（仅管理员可见）
   response_time_ms?: number | null
   first_byte_time_ms?: number | null
+  end_to_end_time_ms?: number | null
+  end_to_end_first_byte_time_ms?: number | null
   updated_at?: string | null
   response_time_updated_at?: string | null
   is_stream: boolean
@@ -357,6 +359,8 @@ export const meApi = {
       rate_multiplier?: number | null
       response_time_ms: number | null
       first_byte_time_ms: number | null
+      end_to_end_time_ms?: number | null
+      end_to_end_first_byte_time_ms?: number | null
       updated_at?: string | null
       response_time_updated_at?: string | null
       status_code?: number | null

frontend/src/api/usage.ts

@@ -29,6 +29,10 @@ export interface UsageRecord {
   total_tokens: number
   cost?: number
   response_time?: number
+  response_time_ms?: number | null
+  first_byte_time_ms?: number | null
+  end_to_end_time_ms?: number | null
+  end_to_end_first_byte_time_ms?: number | null
   created_at: string
   updated_at?: string | null
   response_time_updated_at?: string | null
@@ -554,6 +558,8 @@ export const usageApi = {
       rate_multiplier?: number | null
       response_time_ms: number | null
       first_byte_time_ms: number | null
+      end_to_end_time_ms?: number | null
+      end_to_end_first_byte_time_ms?: number | null
       updated_at?: string | null
       response_time_updated_at?: string | null
       status_code?: number | null