fix: adapt live-artifact tests and iframe guard to upstream drift

- create_file tool arg is `path` upstream, not `file_path`; the outbound
  codeapi payload keeps `file_path`.
- Capture `contentWindow` once in the handshake guard: the old check
  passed when both it and `event.source` were null.

client/src/components/Artifacts/LiveArtifactPreview.tsx

@@ -132,8 +132,8 @@ export default function LiveArtifactPreview({
   // page can't produce the token, so it can never drive the bridge.
   useEffect(() => {
     const onMessage = (event: MessageEvent) => {
-      const frame = iframeRef.current;
-      if (!frame || event.source !== frame.contentWindow) {
+      const frameWindow = iframeRef.current?.contentWindow;
+      if (!frameWindow || event.source !== frameWindow) {
         return;
       }
       if (event.data?.type !== 'librechat:ready' || event.data.token !== token) {
@@ -160,7 +160,7 @@ export default function LiveArtifactPreview({
           requestTool({ id: data.id, name: data.name, args: data.args ?? {}, port: channel.port1 });
         }
       };
-      frame.contentWindow.postMessage({ type: 'librechat:init', token }, '*', [channel.port2]);
+      frameWindow.postMessage({ type: 'librechat:init', token }, '*', [channel.port2]);
     };
     window.addEventListener('message', onMessage);
     return () => {

packages/api/src/agents/handlers.spec.ts

@@ -2268,7 +2268,7 @@ describe('createToolExecuteHandler', () => {
           id: 'call_create_html',
           name: 'create_file',
           args: {
-            file_path: '/mnt/data/dash.html',
+            path: '/mnt/data/dash.html',
             content: '<h1>hi</h1>',
             mcp_tools: ['list_prs_mcp_github', 'not-an-mcp-tool', 'send_msg_mcp_slack'],
           },
@@ -2298,7 +2298,7 @@ describe('createToolExecuteHandler', () => {
           id: 'call_create_escalate',
           name: 'create_file',
           args: {
-            file_path: '/mnt/data/dash.html',
+            path: '/mnt/data/dash.html',
             content: '<h1>hi</h1>',
             // delete_repo_mcp_github is not in the agent's toolRegistry → dropped.
             mcp_tools: ['list_prs_mcp_github', 'delete_repo_mcp_github'],
@@ -2326,7 +2326,7 @@ describe('createToolExecuteHandler', () => {
           id: 'call_create_txt',
           name: 'create_file',
           args: {
-            file_path: '/mnt/data/data.txt',
+            path: '/mnt/data/data.txt',
             content: 'plain',
             mcp_tools: ['list_prs_mcp_github'],
           },