fix(bus): acquire PubSub subscription eagerly to close /event race (#27959)

packages/opencode/src/server/routes/instance/httpapi/handlers/event.ts

@@ -20,10 +20,11 @@ function eventData(data: unknown): Sse.Event {
 
 function eventResponse(bus: Bus.Interface) {
   return Effect.gen(function* () {
-    const context = yield* Effect.context()
-
-    const events = bus.subscribeAll().pipe(
-      Stream.provideContext(context),
+    // Subscribe eagerly: the bus subscription is acquired in the request scope
+    // at this yield, so any publish from now on is queued for the body-pump
+    // fiber to drain — closing the race where Stream.concat(server.connected,
+    // lazy-subscribe) used to drop publishes in the prefix-consume window.
+    const events = (yield* bus.subscribeAll()).pipe(
       Stream.takeUntil((event) => event.type === Bus.InstanceDisposed.type),
     )
     const heartbeat = Stream.tick("10 seconds").pipe(