feat: Create MultiInputStream API primitive (#1036)

Author: toubatbrian

.changeset/neat-parents-develop.md

@@ -0,0 +1,5 @@
+---
+"@livekit/agents": patch
+---
+
+feat: Create MultiInputStream API primitive

agents/src/stream/index.ts

@@ -4,4 +4,5 @@
 export { DeferredReadableStream } from './deferred_stream.js';
 export { IdentityTransform } from './identity_transform.js';
 export { mergeReadableStreams } from './merge_readable_streams.js';
+export { MultiInputStream } from './multi_input_stream.js';
 export { createStreamChannel, type StreamChannel } from './stream_channel.js';