[bug] Run not working in BAML Playground in VS Code - Unspecified error code: 2 builder error

[wf-jaxley]

Product

BAML

Describe the bug

In VS Code, when I click Run in the BAML playground, I get an error:

Unspecified error code: 2 builder error

I have no data beyond that error what is causing it so don't know how to resolve it.

If I run the tests using baml-cli, they work fine:

baml-cli test --from baml_src
....
INFO: Test results:
---------------------------------------------------------
function VerifyCode
1 tests (1 ✅)
  13.89s PASSED       VerifyCode::TestVerifyCode
     baml_src/main.baml:73
---------------------------------------------------------
INFO: Test run completed, 1 tests (1 ✅)

I've tried turning the proxy on/off in UI and config but that doesn't change the message.

Version: 1.116.0 (Universal)
Commit: 560a9dba96f961efea7b1612916f89e5d5d4d679
Date: 2026-04-15T00:28:13Z
Electron: 39.8.7
ElectronBuildId: 13797146
Chromium: 142.0.7444.265
Node.js: 22.22.1
V8: 14.2.231.22-electron.0
OS: Darwin arm64 25.3.0

baml-py version: 0.220.0

boundary.baml-extension version: 0.220.0

Is there more info on troubleshooting? I've seen this error come up a couple times in previous issues that are supposedly resolved.

Reproduction Steps

1. baml-cli init a new project
2. open project in VS Code
3. open BAML playground
4. navigate to the resume.baml sample
5. click on the test class
6. in BAML playground, click Run; observe the error message

BAML Version

0.220.0

Language/Framework

Python

LLM Provider

OpenAI

LLM Model

gpt-5

Operating System

macOS

Browser

Chrome

Code Editor

VS Code

[linear]

BAML-597

[hellovai]

hi @wf-jaxley thanks for reporting this.
This often happens when you're running the BAML playground inside a web container that runs VS Code or a remote box that's pointing to VS Code (its usually a CORS issue).

One debugging technique, you can use Developer Tools to inspect all network requests made by the playground:

if you an share that with us we can debug much better!