WebSocket proxy error on Windows after using `marimo new <prompt>` command

[Haleshot]

Describe the bug

While the fix in PR #4447 now successfully creates and launches notebooks based on prompts via the marimo new <prompt> command on Windows, there's a remaining WebSocket connection issue that appears in the terminal after notebook launch:

[E 250409 21:39:09 middleware:486] WebSocket proxy error: Multiple exceptions: [Errno 10061] Connect call failed ('::1', 3123, 0, 0), [Errno 10061] Connect call failed ('127.0.0.1', 3123)

Additionally, the notebook contents are initially stale — cells are created with relevant code based on the prompt but require manual execution (clicking the run button) to actually run (this is related to the error shown above I presume).

Expected behavior:

• No WebSocket errors should appear after notebook creation
• Notebook cells should automatically execute after creation.

Environment

{
  "marimo": "0.12.6",
  "OS": "Windows",
  "OS Version": "11",
  "Processor": "AMD64 Family 25 Model 80 Stepping 0, AuthenticAMD",
  "Python Version": "3.11.4",
  "Binaries": {
    "Browser": "132.0.6834.111",
    "Node": "v22.12.0"
  },
  "Dependencies": {
    "click": "8.1.3",
    "docutils": "0.21.2",
    "itsdangerous": "2.2.0",
    "jedi": "0.19.2",
    "markdown": "3.7",
    "narwhals": "1.22.0",
    "packaging": "24.2",
    "psutil": "6.1.1",
    "pygments": "2.19.1",
    "pymdown-extensions": "10.14",
    "pyyaml": "6.0.2",
    "ruff": "0.9.1",
    "starlette": "0.45.2",
    "tomlkit": "0.13.2",
    "typing-extensions": "4.12.2",
    "uvicorn": "0.34.0",
    "websockets": "14.1"
  },
  "Optional Dependencies": {
    "anywidget": "0.9.13",
    "duckdb": "1.2.0",
    "pandas": "2.2.3",
    "polars": "1.21.0",
    "pyarrow": "18.1.0"
  },
  "Experimental Flags": {
    "tracing": true,
    "rtc": false,
    "lsp": true,
    "chat_sidebar": true,
    "multi_column": true
  }
}

Code to reproduce

marimo edit "Plot an interactive 3D surface with matplotlib."