Sub-agent launcher rejects configured gpt-5.6-luna while direct Codex Luna run succeeds

Summary

The Codex multi-agent sub-agent launcher rejects gpt-5.6-luna as an unknown model even though Luna is configured for the Builder role and a direct Codex Luna Max run succeeds on the same machine and ChatGPT account.

Environment

• macOS 26.5.1, arm64
• Codex desktop-bundled CLI: 0.147.0-alpha.6.5
• Authentication: ChatGPT
• Global config: model = "gpt-5.6-luna", model_reasoning_effort = "max"
• Global and project Builder definitions: model = "gpt-5.6-luna", model_reasoning_effort = "max"
• Project sub-agent defaults also request Luna Max
• Desktop app has been restarted several times without changing behavior

Reproduction

1. From a GPT-5.6 task, create a sub-agent with the built-in Builder role, or explicitly request model gpt-5.6-luna with Max reasoning.
2. The launcher rejects the request before the agent starts.

Observed errors:

Unknown model `gpt-5.6-luna` for spawn_agent. Available models: gpt-5.6-sol, gpt-5.6-terra

and the built-in Builder role cannot start because that role is fixed to Luna.

Control test

A direct ephemeral Codex run succeeds:

codex exec --ephemeral --json --skip-git-repo-check \
  -m gpt-5.6-luna \
  -c model_reasoning_effort='"max"' \
  -s read-only \
  "Reply with exactly LUNA_OK and nothing else."

Observed final agent message:

LUNA_OK

This suggests Luna is available to the account and local Codex runtime, but missing from the multi-agent launcher allowlist or capability snapshot for the active task.

Expected behavior

The sub-agent launcher should honor a valid configured Luna Max Builder, or return a specific explanation if Luna is intentionally unavailable for that sub-agent runtime.

Privacy

No repository code, credentials, account identifiers, or proprietary data are included in this report.

Start at the multi-agent sub-agent launcher and its spawn_agent model validation, then compare that path with the successful codex exec --ephemeral control command. Done means a configured gpt-5.6-luna Builder starts successfully, or the launcher provides a specific explanation when the model is unavailable.