fix(chat): revert cancelGeneration-on-disconnect

req.on("close") was firing for healthy SSE connections in this
Node/Express setup, which cancelled the in-flight agent the client was
still listening to and made even msg #1 fail after a fresh reload.
Keep the beginGeneration (no dispose) change from the same commit —
that one's correct.

packages/dashboard/src/routes/register-chat-routes.ts

@@ -560,15 +560,6 @@ export function registerChatRoutes(ctx: ApiRoutesContext, deps: ChatRouteDeps):
       // Handle client disconnect
       req.on("close", () => {
         unsubscribe();
-        // If the response hasn't been ended (i.e. the generation was still
-        // streaming when the browser disconnected — tab close, navigation,
-        // network drop), cancel the agent so it doesn't keep running with
-        // nobody listening. Otherwise the next request for this session sees a
-        // stale `activeGenerations` entry and races against the lingering
-        // agent for the same CLI session file.
-        if (!res.writableEnded) {
-          chatManager.cancelGeneration(sessionId);
-        }
       });
 
       // Send heartbeat every 30s to keep connection alive