Remove double stringify for string tool result (#537)

Author: toubatbrian

.changeset/olive-ears-live.md

@@ -0,0 +1,5 @@
+---
+'@livekit/agents-plugin-openai': patch
+---
+
+remove duplicated stringify for string tool output

plugins/openai/src/llm.ts

@@ -638,8 +638,9 @@ const buildMessage = async (msg: llm.ChatMessage, cacheKey: any) => {
 
   if (msg.role === llm.ChatRole.TOOL) {
     try {
-      const toolCallOutput = JSON.stringify(msg.content);
-      oaiMsg.content = toolCallOutput;
+      const serializedContent =
+        typeof msg.content === 'string' ? msg.content : JSON.stringify(msg.content);
+      oaiMsg.content = serializedContent;
     } catch (e) {
       throw Error(`Tool call output is not JSON serializable: ${e}`);
     }