[inference] fix: streaming conversational with auto provider (#1833)

Follow-up to #1810 

Applies the same changes to the streaming counterpart

Author: SBrandeis

packages/inference/src/tasks/nlp/chatCompletionStream.ts

@@ -3,6 +3,8 @@ import { resolveProvider } from "../../lib/getInferenceProviderMapping.js";
 import { getProviderHelper } from "../../lib/getProviderHelper.js";
 import type { BaseArgs, Options } from "../../types.js";
 import { innerStreamingRequest } from "../../utils/request.js";
+import type { ConversationalTaskHelper, TaskProviderHelper } from "../../providers/providerHelper.js";
+import { AutoRouterConversationalTask } from "../../providers/providerHelper.js";
 
 /**
  * Use to continue text from a prompt. Same as `textGeneration` but returns generator that can be read one token at a time
@@ -11,8 +13,14 @@ export async function* chatCompletionStream(
 	args: BaseArgs & ChatCompletionInput,
 	options?: Options
 ): AsyncGenerator<ChatCompletionStreamOutput> {
-	const provider = await resolveProvider(args.provider, args.model, args.endpointUrl);
-	const providerHelper = getProviderHelper(provider, "conversational");
+	let providerHelper: ConversationalTaskHelper & TaskProviderHelper;
+	if (!args.provider || args.provider === "auto") {
+		// Special case: we have a dedicated auto-router for conversational models. No need to fetch provider mapping.
+		providerHelper = new AutoRouterConversationalTask();
+	} else {
+		const provider = await resolveProvider(args.provider, args.model, args.endpointUrl);
+		providerHelper = getProviderHelper(provider, "conversational");
+	}
 	yield* innerStreamingRequest<ChatCompletionStreamOutput>(args, providerHelper, {
 		...options,
 		task: "conversational",