Bridge look_up_username_hash to app languages

Co-authored-by: Jordan Rose <jrose@signal.org>

node/ts/test/chat/ServiceTestUtils.ts

@@ -0,0 +1,45 @@
+//
+// Copyright 2025 Signal Messenger, LLC.
+// SPDX-License-Identifier: AGPL-3.0-only
+//
+
+import * as Native from '../../../Native';
+import { TokioAsyncContext, UnauthenticatedChatConnection } from '../../net';
+
+/**
+ * A requirement that `Sub` not contain any properties that aren't in `Super`, or properties with
+ * different types.
+ *
+ * Use {@link PickSubset} to generate a type that a `Super` instance can be assigned to. This will
+ * be equivalent to `Sub` in practice, but TypeScript can only figure that out in concrete contexts.
+ */
+type Subset<Super, Sub> = Partial<Super> & {
+  [K in Exclude<keyof Sub, keyof Super>]: never;
+};
+
+/** See {@link Subset}. */
+type PickSubset<Super, Sub extends Subset<Super, Sub>> = Pick<
+  Super,
+  keyof Super & keyof Sub
+>;
+
+/**
+ * Makes an unauth connection with a fake remote, but forces the caller to specify which APIs they
+ * need from the connection.
+ */
+export function connectUnauth<
+  // The default of `object` forces the caller to provide a type explicitly to access any members of
+  // the result.
+  Api extends Subset<UnauthenticatedChatConnection, Api> = object
+>(
+  tokio: TokioAsyncContext
+): [
+  PickSubset<UnauthenticatedChatConnection, Api>,
+  Native.Wrapper<Native.FakeChatRemoteEnd>
+] {
+  return UnauthenticatedChatConnection.fakeConnect(tokio, {
+    onConnectionInterrupted: () => {},
+    onIncomingMessage: () => {},
+    onQueueEmpty: () => {},
+  });
+}