macOS desktop Browser MCP consistently returns `Transport closed` while Codex CLI succeeds on the same machine

Summary

On macOS, Codex desktop's built-in Browser MCP consistently fails with a Transport closed error on brand new threads.

On the same machine, Codex CLI succeeds against the same Browser MCP setup.

Environment

• Date observed: 2026-03-21
• OS: macOS 15.7.2 (24G322)
• Codex CLI: 0.115.0
• Browser MCP runtime: 0.1.3
• Browser: Google Chrome + Browser MCP extension connected

Reproduction

1. Open Codex desktop on macOS.
2. Open a brand new thread.
3. Use the built-in Browser MCP tool only.
4. Call browser_snapshot.

Actual

The desktop thread fails immediately with:

tool call error: tool call failed for `browsermcp/browser_snapshot`

Caused by:
    Transport closed

Expected
Desktop Browser MCP should either return a snapshot or a meaningful extension-connection error, and it should behave consistently with Codex CLI on the same machine.

What I verified locally
The Browser MCP wrapper/runtime is healthy.
The Browser MCP extension is connected in Chrome.
The local wrapper now launches Browser MCP 0.1.3.
resources/list and resources/templates/list both succeed locally.
browser_snapshot succeeds from Codex CLI on the same machine.
Wrapper stderr is clean; I no longer see the earlier RangeError: Maximum call stack size exceeded from Browser MCP 0.1.2.
CLI workaround that succeeds
cd /tmp
codex exec --json --skip-git-repo-check 'Use the browser MCP tools only. Call browser_snapshot. If a tool call fails, report the exact error and stop.'
Notes
This looks more like a Codex desktop MCP transport/lifecycle problem than a Browser MCP install problem, because:

the same Browser MCP config works from CLI
a fresh desktop thread still fails
the local Browser MCP runtime is responsive and not crashing
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