fix(sdk-js): reset isLoading state when switching threads mid-run (#1790)

.changeset/gentle-dolls-push.md

@@ -0,0 +1,5 @@
+---
+"@langchain/langgraph-sdk": patch
+---
+
+Ensure `isLoading` is set to `false` when cancelling the stream due to thread ID change

libs/sdk/src/ui/manager.ts

@@ -358,7 +358,7 @@ export class StreamManager<
     this.abortRef = new AbortController();
 
     // Set the stream state to null
-    this.setState({ error: undefined, values: null });
+    this.setState({ error: undefined, values: null, isLoading: false });
 
     // Clear any pending messages
     this.messages.clear();