fix: surface disconnect error instead of queue-closed when deferred already failed

When a client disconnects while a request is pending, disconnect() fails the
deferred with PreviewAutomationClientDisconnectedError before shutting down the
queue. If invoke()'s Queue.offer then observes the shutdown, it would previously
return PreviewAutomationRequestQueueClosedError, masking the more specific
disconnect error already recorded on the deferred.

Use Deferred.poll to check whether the deferred was already completed before
falling back to the queue-closed error, ensuring callers receive the correct
PreviewAutomationClientDisconnectedError.

Author: cursoragent

apps/server/src/mcp/PreviewAutomationBroker.ts

@@ -375,7 +375,11 @@ export const make = Effect.gen(function* PreviewAutomationBrokerMake() {
         timeoutMs,
       });
       if (!offered) {
-        return yield* new PreviewAutomationRequestQueueClosedError(requestContext);
+        const completed = yield* Deferred.poll(deferred);
+        return yield* Option.match(completed, {
+          onNone: () => Effect.fail(new PreviewAutomationRequestQueueClosedError(requestContext)),
+          onSome: (effect) => effect as Effect.Effect<A, PreviewAutomationError>,
+        });
       }
       const result = yield* Deferred.await(deferred).pipe(Effect.timeoutOption(timeoutMs));
       return yield* Option.match(result, {