Windows: multi_agent_v2 breaks custom Responses provider in Codex 0.139.0

Windows: multi_agent_v2 breaks custom Responses provider in Codex 0.139.0

Summary

After upgrading Codex CLI from 0.137.0 to 0.139.0, requests fail when using a custom OpenAI-compatible provider with wire_api = "responses" and features.multi_agent_v2.enabled = true.

Disabling multi_agent_v2 makes the same custom provider work again.

Environment

• OS: Windows
• Codex CLI: codex-cli 0.139.0
• Provider: custom OpenAI-compatible provider
• Wire API: responses
• Model: custom model configured as gpt-5.5
• Plugin state: issue occurs with user config loaded; SessionStart hook failure may also be displayed when a session-start plugin is enabled

Relevant config shape

model = "gpt-5.5"
model_provider = "custom"
model_reasoning_effort = "xhigh"

[features.multi_agent_v2]
enabled = true

[model_providers.custom]
name = "custom"
base_url = "https://<redacted>/v1"
requires_openai_auth = true
wire_api = "responses"

Reproduction

1. Install Codex CLI 0.139.0.
2. Configure a custom provider using wire_api = "responses".
3. Enable:

[features.multi_agent_v2]
enabled = true

1. Run:

codex exec --skip-git-repo-check "Reply OK"

Observed behavior

With the full user config and multi_agent_v2 enabled, Codex fails with one of these errors:

ERROR: {"error":{"message":"","type":"bad_response_status_code","param":"","code":"bad_response_status_code"}}

or:

ERROR: Reconnecting... 1/5
ERROR: Reconnecting... 2/5
ERROR: Reconnecting... 3/5
ERROR: Reconnecting... 4/5
ERROR: Reconnecting... 5/5
ERROR: stream disconnected before completion: stream closed before response.completed

When a SessionStart hook is enabled, the CLI may also print:

hook: SessionStart
hook: SessionStart Failed

However, manually running the hook exits successfully in under one second, so the hook appears to be a secondary symptom rather than the root cause.

Expected behavior

Codex should either:

• support multi_agent_v2 with custom responses providers, or
• ignore/disable the feature for unsupported providers with a clear error message.

Workaround

Set:

[features.multi_agent_v2]
enabled = false

After this change, the same installation and provider can successfully run:

codex exec --skip-git-repo-check -o $env:TEMP\codex-verify-last-message.txt "Reply OK"
Get-Content $env:TEMP\codex-verify-last-message.txt

The output is:

OK