Codex App Browser fails on macOS when node_repl receives file URL sandboxCwd #29348

What version of the Codex App are you using?

Codex App / Browser plugin release observed locally: 26.616.41845

What subscription do you have?

Not included here; this report is about local Codex App / bundled MCP runtime behavior.

What platform is your computer?

macOS

Additional local runtime details:

• Bundled Node: v24.14.0
• Bundled node_repl path: /Applications/Codex.app/Contents/Resources/cua_node/bin/node_repl
• Browser backend: iab
• Local URL tested: http://127.0.0.1:5173/

What issue are you seeing?

Codex App can open the in-app browser manually, and the Browser backend appears ready, but model-side Browser plugin use fails through the bundled node_repl MCP path.

I observed two related sandbox metadata compatibility failures around codex/sandbox-state-meta:

1. node_repl rejects missing sandboxPolicy:

Mcp error: -32602: js: codex/sandbox-state-meta: missing field sandboxPolicy

2. sandboxCwd can be passed as a file:// URL:

{
  "sandboxCwd": "file:///Users/zhangyifan/self_driven"
}

The bundled runtime then fails while launching Node:

failed to start Node runtime: No such file or directory (os error 2)

My root-cause hypothesis is that the bundled node_repl expects sandboxCwd to already be a native filesystem path, but Codex App / the sender side can pass a file:// URL. I also found a metadata shape mismatch around sandboxPolicy.type: a payload with workspaceWrite is rejected by the bundled node_repl, while workspace-write is accepted.

What steps can reproduce the bug?

1. Use Codex App on macOS with the bundled Browser plugin.
2. Start or have a local web app available, for example http://127.0.0.1:5173/.
3. Manually opening the in-app browser works.
4. Ask Codex to use the Browser plugin / in-app Browser against the local page.
5. The model-side Browser flow fails in the node_repl MCP path with sandbox metadata errors.

I verified a local workaround by setting CODEX_NODE_REPL_PATH to a wrapper that sits between Codex App and the bundled node_repl. The wrapper normalized the metadata before forwarding:

• sandboxCwd: file:///Users/... -> /Users/...
• sandboxPolicy.type: workspaceWrite -> workspace-write
• filled in missing sandbox metadata when safely derivable

After that workaround:

• mcp__node_repl__js executed successfully
• nodeRepl.cwd was /Users/zhangyifan/self_driven
• Browser runtime connected to iab
• Codex could open and read http://127.0.0.1:5173/
• The page title was read as Self Driven

What is the expected behavior?

Codex App and bundled node_repl should agree on the codex/sandbox-state-meta payload shape.

In particular, node_repl or the sender side should handle:

• sandboxCwd as either a native filesystem path or a file:// URL, normalizing to the native path before launching Node.
• sandboxPolicy.type values consistently, or compatibly accept both the app-server/API style workspaceWrite and the legacy/sandbox-mode style workspace-write where this metadata boundary requires it.
• missing required metadata with a clear validation error that identifies the missing field and expected shape, rather than surfacing as failed to start Node runtime: No such file or directory.

Additional information

I searched existing issues and found nearby Windows reports about missing field sandboxPolicy, but I did not find one covering this macOS sandboxCwd: file://... launch failure.

The bundled node_repl receiver implementation does not appear to be present in the public repo, but the public sender-side code that builds codex/sandbox-state-meta is present.

I prepared a small sender-side patch for reference, but did not open a PR because docs/contributing.md says unsolicited PRs are closed without review:

main...ruarua6666:codex/normalize-node-repl-sandbox-meta

That reference patch changes the public sender-side metadata to:

• include a legacy-compatible sandboxPolicy
• serialize sandboxCwd as an inferred native filesystem path instead of a file:// URI
• update the existing RMCP integration assertion for sandbox metadata