`exec` subcommand doesn't detect `--model` argument specified before it.

Question

### What version of Codex is running?

codex-cli 0.21.0

### Which model were you using?

gpt-4.1

### What platform is your computer?

Darwin 24.6.0 arm64 arm

### What steps can reproduce the bug?

```
$ codex -m gpt-4.1 exec --skip-git-repo-check "hello"

[2025-08-14T16:01:35] OpenAI Codex v0.21.0 (research preview)
--------
workdir: ...
model: gpt-5
provider: openai
approval: never
sandbox: read-only
reasoning effort: medium
reasoning summaries: auto
--------
```

### What is the expected be

`exec` subcommand doesn't detect `--model` argument specified before it.

What version of Codex is running?

Which model were you using?

What platform is your computer?

What steps can reproduce the bug?

What is the expected behavior?

What do you see instead?

Additional information