fix: make toolset switching atomic to prevent tool desync race (#648)

Co-authored-by: Letta <noreply@letta.com>

src/agent/message.ts

@@ -8,7 +8,10 @@ import type {
   ApprovalCreate,
   LettaStreamingResponse,
 } from "@letta-ai/letta-client/resources/agents/messages";
-import { getClientToolsFromRegistry } from "../tools/manager";
+import {
+  getClientToolsFromRegistry,
+  waitForToolsetReady,
+} from "../tools/manager";
 import { isTimingsEnabled } from "../utils/timing";
 import { getClient } from "./client";
 
@@ -42,6 +45,10 @@ export async function sendMessageStream(
 
   const client = await getClient();
 
+  // Wait for any in-progress toolset switch to complete before reading tools
+  // This prevents sending messages with stale tools during a switch
+  await waitForToolsetReady();
+
   let stream: Stream<LettaStreamingResponse>;
 
   if (process.env.DEBUG) {