chore: Fix types in tests 3/N.

src/gateway/test-helpers.server.ts

@@ -296,9 +296,20 @@ export async function occupyPort(): Promise<{
   });
 }
 
-export function onceMessage<T = unknown>(
+type GatewayTestMessage = {
+  type?: string;
+  id?: string;
+  ok?: boolean;
+  event?: string;
+  payload?: Record<string, unknown> | null;
+  seq?: number;
+  stateVersion?: Record<string, unknown>;
+  [key: string]: unknown;
+};
+
+export function onceMessage<T extends GatewayTestMessage = GatewayTestMessage>(
   ws: WebSocket,
-  filter: (obj: unknown) => boolean,
+  filter: (obj: T) => boolean,
   // Full-suite runs can saturate the event loop (581+ files). Keep this high
   // enough to avoid flaky RPC timeouts, but still fail fast when a response
   // never arrives.
@@ -312,12 +323,12 @@ export function onceMessage<T = unknown>(
       reject(new Error(`closed ${code}: ${reason.toString()}`));
     };
     const handler = (data: WebSocket.RawData) => {
-      const obj = JSON.parse(rawDataToString(data));
+      const obj = JSON.parse(rawDataToString(data)) as T;
       if (filter(obj)) {
         clearTimeout(timer);
         ws.off("message", handler);
         ws.off("close", closeHandler);
-        resolve(obj as T);
+        resolve(obj);
       }
     };
     ws.on("message", handler);