GPT Sol and Terra threads cannot spawn Luna subagents because of Luna Multi Agent version

What version of Codex CLI is running?

0.144.6

What subscription do you have?

Prolite

Which model were you using?

gpt-5.6-sol

What platform is your computer?

Windows

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

Terminal app

Codex doctor report

What issue are you seeing?

gpt-5.6-sol and gpt-5.6-terra models are unable to use the spawn_agent tool to create gpt-5.6-luna subagents

What steps can reproduce the bug?

1. Start gpt-5.6-sol thread
2. Ask it to create a default gpt-5.6-luna subagent

What is the expected behavior?

Luna subagents should be available to spawn from Sol/Terra parents

Additional information

I believe this issue stems from the commit `92938d880e`, where it says "Restrict spawned-agent models to the active backend", luna is classified as using multi_agent version v1, instead of v2 like its other 5.6 counterparts. The v2 check is in codex/codex-rs/core/src/tools/handlers/multi_agent_common.rs on line 33:

pub(crate) fn model_supports_multi_agent_backend(
    model: &ModelPreset,
    multi_agent_version: MultiAgentVersion,
) -> bool {
    multi_agent_version != MultiAgentVersion::V2
        || model.multi_agent_version == Some(multi_agent_version)
}

But the correct behavior patch would be to change gpt-5.6-luna to use multi_agent v2 if thats the intended future route, or switch gpt-5.6-sol and gpt-5.6-terra to multi agent v1