Improved sandbox diagnostics

What version of Codex CLI is running?

codex-cli 0.104.0

What subscription do you have?

plus

Which model were you using?

gpt-5.3-codex

What platform is your computer?

apple container on arm64 macos

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

_No response_

What issue are you seeing?

I run an agent in apple container. I noticed strange behavior of sandbox. When I run codex sandbox linux mkdir -p .codex I got this error:

thread 'main' (12504) panicked at linux-sandbox/src/linux_run_main.rs:138:9:
error applying legacy Linux sandbox restrictions: Sandbox(LandlockRestrict)

Would be nice to at least warn that sandbox can't be applied to the current directory.

What steps can reproduce the bug?

Run codex sandbox linux mkdir -p .codex in a directory where this directory doesn't exist

What is the expected behavior?

Error due to sandbox forbidding this operation

Additional information

_No response_