diff --git a/frontend/app/[locale]/newchat/adapter/conversation-thread-list-adapter.tsx b/frontend/app/[locale]/newchat/adapter/conversation-thread-list-adapter.tsx
index eee8573277..68b46f9550 100644
--- a/frontend/app/[locale]/newchat/adapter/conversation-thread-list-adapter.tsx
+++ b/frontend/app/[locale]/newchat/adapter/conversation-thread-list-adapter.tsx
@@ -1377,6 +1377,16 @@ export const conversationThreadListAdapter: RemoteThreadListAdapter = {
     };
   },
 
+  // New conversations do not have a backend ID until their first agent run.
+  // Accept metadata updates so assistant-ui can retain the selected agent in
+  // its local thread state while users switch between conversations.
+  async updateCustom(
+    _remoteId: string,
+    _custom: Record<string, unknown> | undefined
+  ): Promise<void> {
+    return;
+  },
+
   async rename(remoteId: string, newTitle: string): Promise<void> {
     const candidateId = await waitForServerConversationId(remoteId);
     const conversationId = Number(candidateId);
diff --git a/frontend/app/[locale]/newchat/page.tsx b/frontend/app/[locale]/newchat/page.tsx
index 3f60dd1a5a..c577ab0eff 100644
--- a/frontend/app/[locale]/newchat/page.tsx
+++ b/frontend/app/[locale]/newchat/page.tsx
@@ -700,6 +700,11 @@ const HomeContent: FC<{
     async (agent: Agent) => {
       shouldRestoreAgentRef.current = true;
       await runtime.threads.switchToNewThread();
+      const thread = runtime.threads.getItemById(
+        runtime.threads.getState().mainThreadId
+      );
+      await thread.initialize();
+      await thread.updateCustom({ agentId: agent.id });
       onAgentSelected(agent);
     },
     [runtime, onAgentSelected]
diff --git a/frontend/services/storageService.ts b/frontend/services/storageService.ts
index e64e1c2bf9..a2bdb34150 100644
--- a/frontend/services/storageService.ts
+++ b/frontend/services/storageService.ts
@@ -168,9 +168,6 @@ export async function fetchImageBlob(url: string): Promise<Blob> {
   const apiUrl = convertImageUrlToApiUrl(url);
   log.info(`[fetchImageBlob] input=${url}, apiUrl=${apiUrl}`);
   const response = await fetch(apiUrl);
-  log.info(
-    `[fetchImageBlob] status=${response.status}, contentType=${response.headers.get("content-type")}`
-  );
   if (!response.ok) {
     throw new Error(
       `Failed to fetch image: ${response.status} ${response.statusText}`
diff --git a/frontend/tests/newchatThreadAgentBinding.test.ts b/frontend/tests/newchatThreadAgentBinding.test.ts
new file mode 100644
index 0000000000..9a3100aa10
--- /dev/null
+++ b/frontend/tests/newchatThreadAgentBinding.test.ts
@@ -0,0 +1,36 @@
+import assert from "node:assert/strict";
+import { readFile } from "node:fs/promises";
+import test from "node:test";
+
+const pagePath = new URL("../app/[locale]/newchat/page.tsx", import.meta.url);
+const adapterPath = new URL(
+  "../app/[locale]/newchat/adapter/conversation-thread-list-adapter.tsx",
+  import.meta.url
+);
+
+test("binds an agent selected for a new thread to that thread's metadata", async () => {
+  const page = await readFile(pagePath, "utf8");
+
+  assert.match(
+    page,
+    /thread\.updateCustom\(\{\s*agentId:\s*agent\.id\s*\}\)/
+  );
+});
+
+test("initializes a new thread before storing its selected agent", async () => {
+  const page = await readFile(pagePath, "utf8");
+
+  assert.match(
+    page,
+    /const thread = runtime\.threads\.getItemById\([\s\S]*await thread\.initialize\(\);[\s\S]*await thread\.updateCustom\(/
+  );
+});
+
+test("supports storing an agent on a new thread before the conversation exists on the server", async () => {
+  const adapter = await readFile(adapterPath, "utf8");
+
+  assert.match(
+    adapter,
+    /async updateCustom\(\s*_remoteId: string,\s*_custom: Record<string, unknown> \| undefined\s*\): Promise<void>/
+  );
+});