Enabling standalone_web_search causes tools.namespace collision with reserved web namespace

What version of Codex CLI is running?

codex-cli 0.139.0

What subscription do you have?

ChatGPT Plus

Which model were you using?

gpt-5.5

What platform is your computer?

Linux 7.0.11-100.fc43.x86_64 x86_64 unknown,Fedora Linux 43 Cloud Edition.

What terminal emulator and version are you using (if applicable)?

SSH session, TERM=xterm-256color

Codex doctor report

overallStatus: ok
codexVersion: 0.139.0
auth mode: ChatGPT
model provider: OpenAI

What issue are you seeing?

Enabling the recognized standalone_web_search feature makes every model
request fail with HTTP 400:

{
  "type": "error",
  "error": {
    "type": "invalid_request_error",
    "message": "Invalid Value: 'tools.namespace'. User-defined namespace 'web' collides with an existing tool namespace.",
    "param": "tools.namespace"
  },
  "status": 400
}

Removing standalone_web_search = true and restarting Codex fixes the error.
Normal hosted web search continues to work with web_search = "live".

No configured MCP server uses the web namespace. The only configured MCP
server is openaiDeveloperDocs.

What steps can reproduce the bug?

1. Install and authenticate Codex CLI 0.139.0 using ChatGPT auth.
2. Add this configuration to ~/.codex/config.toml:

model = "gpt-5.5"
web_search = "live"

[features]
code_mode = true
standalone_web_search = true

1. Confirm the flag is recognized:

codex features list

It reports:

standalone_web_search    under development    true

1. Restart Codex and send any prompt.
2. Observe the HTTP 400 namespace-collision error above.
3. Remove standalone_web_search = true, restart, and retry. Requests work.

What is the expected behavior?

Codex should register standalone web search without colliding with the
Responses runtime's existing web namespace. Code mode should be able to call
standalone web search as described by PR #26719.

Additional information

• Install method: standalone Linux x86_64 binary.
• codex doctor --json reports overall status ok.
• Direct hosted web search works when the preview flag is disabled.
• The failure appears isolated to the preview extension registering web.run

while the runtime already has a reserved web tool namespace.

• Related PR: https://github.com/openai/codex/pull/26719
• Exact public issue searches found no existing report on 2026-06-14.