chore: update documentation in response middleware

packages/proxy/lib/http/response-middleware.ts

@@ -351,14 +351,15 @@ const MaybeSetOriginAgentClusterHeader: ResponseMiddleware = function () {
 
     if (process.env.HTTP_PROXY_TARGET_FOR_ORIGIN_REQUESTS && process.env.HTTP_PROXY_TARGET_FOR_ORIGIN_REQUESTS === origin) {
       // For cypress-in-cypress tests exclusively, we need to bucket all origin-agent-cluster requests
-      // from HTTP_PROXY_TARGET_FOR_ORIGIN_REQUESTS to include Origin-Agent-Cluster=false. This has to due with changed
+      // from HTTP_PROXY_TARGET_FOR_ORIGIN_REQUESTS to include Origin-Agent-Cluster=false. This has to do with changed
       // behavior starting in Chrome 119. The new behavior works like the following:
-      //     If a page did not request an origin-keyed agent cluster, chrome will place it in one
-      //     anyway because a previous request went through without the Origin-Agent-Cluster=false header set.
-      //     At time of writing, documentation detailing this behavior has not been found.
-
+      //    - If the first page from an origin does not set the header,
+      //      then no other pages from that origin will be origin-keyed, even if those other pages do set the header.
+      //    - If the first page from an origin sets the header and is made origin-keyed,
+      //      then all other pages from that origin will be origin-keyed whether they ask for it or not.
       // To work around this, any request that matches the origin of HTTP_PROXY_TARGET_FOR_ORIGIN_REQUESTS
-      // should set the Origin-Agent-Cluster=false header to avoid origin-keyed agent clusters for
+      // should set the Origin-Agent-Cluster=false header to avoid origin-keyed agent clusters.
+      // @see https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Origin-Agent-Cluster for more details.
       this.res.setHeader('Origin-Agent-Cluster', '?0')
     }
   }