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/asl/controllers/researchController.ts

@@ -38,8 +38,8 @@ export async function streamSearch(
   reply.raw.writeHead(200, {
     'Content-Type': 'text/event-stream',
     'Cache-Control': 'no-cache',
-    'Connection': 'keep-alive',
     'Access-Control-Allow-Origin': '*',
+    'X-Accel-Buffering': 'no',
   });
 
   try {