0.137.0 (ChatGPT account): multi_agent_v2 enabled in config.toml breaks every turn with spawn_agent encrypted-tools 400

Summary

With features.multi_agent_v2.enabled = true in ~/.codex/config.toml, every Codex turn fails at API request validation before the model handles the prompt — even when the user does not ask to spawn sub-agents.

Error:

{
  "type": "error",
  "error": {
    "type": "invalid_request_error",
    "message": "Invalid Value: 'tools'. Function 'functions.spawn_agent' declares encrypted parameters but is not configured for encrypted tool use by this model.",
    "param": "tools"
  },
  "status": 400
}

This blocks codex exec background automation (e.g. dispatching Playwright test fixes) because the session never starts.

Environment

• Codex CLI: 0.137.0
• OS: macOS 25.5.0 (Darwin arm64, Apple Silicon)
• Auth: ChatGPT account (codex login status — not API key)
• Model: gpt-5.5 with model_reasoning_effort=high

Config snippet (relevant)

[features]
multi_agent = true

[features.multi_agent_v2]
enabled = true
max_concurrent_threads_per_session = 10000

I do not recall manually enabling multi_agent_v2; it may have been added during a recent CLI/Desktop upgrade (similar reports in openai/codex#27205).

Minimal repro

codex exec --ephemeral --skip-git-repo-check -C /tmp 'Reply exactly: DONE'

Fails immediately with the spawn_agent encrypted-tools 400 above.

Workaround (confirmed locally)

Disable v2 for the invocation:

codex exec --disable multi_agent_v2 ...

Or in ~/.codex/config.toml:

[features.multi_agent_v2]
enabled = false

Legacy multi_agent (v1) subagent flow works after disabling v2.

Expected behavior

Either:

1. The active model/backend supports MultiAgentV2 encrypted tool schemas, or
2. Codex should not expose encrypted v2 tools (spawn_agent, send_message, followup_task) unless the backend is configured for encrypted tool use, or
3. Upgrades should not silently enable multi_agent_v2 while the feature is still under development and incompatible with ChatGPT-account backends.

At minimum, enabling multi_agent_v2 should not make unrelated prompts fail at request validation time.

Related issues

• openai/codex#26753 (closed as v2 not taking bug reports yet — but issue still affects stable users whose config has v2 enabled)
• openai/codex#27205 (same root cause, followup_task variant on 0.138.0)
• openai/codex#27260 (Desktop regression, duplicate)

Impact

Production automation workflows that rely on codex exec (CI agents, Claude Code dispatch, scripted refactors) fail entirely when v2 is enabled — not just when spawning sub-agents.