fix(aia,ssa,asl,infra): harden SSE transport and stabilize attachment context

Deliver SSE protocol hardening for SAE/HTTP2 paths, add graceful shutdown health behavior, and improve SSA retry UX for transient stream failures. For AIA, persist attachment extraction results in database with cache read-through fallback, plus production cache safety guard to prevent memory-cache drift in multi-instance deployments; also restore ASL SR page scrolling behavior.

Made-with: Cursor

backend/src/modules/ssa/routes/chat.routes.ts

@@ -43,11 +43,10 @@ export default async function chatRoutes(app: FastifyInstance) {
       return reply.status(400).send({ error: '消息内容不能为空' });
     }
 
-    // SSE 响应头
+    // SSE 响应头（不设置 Connection，HTTP/2 中为禁止头部）
     reply.raw.writeHead(200, {
       'Content-Type': 'text/event-stream',
       'Cache-Control': 'no-cache',
-      'Connection': 'keep-alive',
       'Access-Control-Allow-Origin': '*',
       'X-Accel-Buffering': 'no',
     });

backend/src/modules/ssa/routes/session.routes.ts

@@ -266,8 +266,8 @@ export default async function sessionRoutes(app: FastifyInstance) {
     reply.raw.writeHead(200, {
       'Content-Type': 'text/event-stream',
       'Cache-Control': 'no-cache',
-      'Connection': 'keep-alive',
       'Access-Control-Allow-Origin': '*',
+      'X-Accel-Buffering': 'no',
     });
 
     const send = (type: string, data: any) => {

backend/src/modules/ssa/routes/workflow.routes.ts

@@ -276,8 +276,8 @@ export default async function workflowRoutes(app: FastifyInstance) {
       reply.raw.writeHead(200, {
         'Content-Type': 'text/event-stream',
         'Cache-Control': 'no-cache',
-        'Connection': 'keep-alive',
-        'Access-Control-Allow-Origin': '*'
+        'Access-Control-Allow-Origin': '*',
+        'X-Accel-Buffering': 'no',
       });
 
       // 发送初始连接确认