Metal devices are invisible inside sandbox on Apple Silicon, which causes false MLX failures
Open 💬 0 comments Opened Apr 6, 2026 by weypro
What version of Codex CLI is running?
latest
What subscription do you have?
plus
Which model were you using?
_No response_
What platform is your computer?
_No response_
What terminal emulator and version are you using (if applicable)?
_No response_
What issue are you seeing?
Inside the sandbox, Metal is not visible to the process. This makes MLX-based checks fail inside the sandbox even though they work in a normal terminal on the same machine.
What steps can reproduce the bug?
Repro in sandbox(codex):
mkdir -p .cache/swift-module .cache/xcode-home
CLANG_MODULE_CACHE_PATH="$PWD/.cache/swift-module" \
HOME="$PWD/.cache/xcode-home" \
swift -e 'import Metal
let all = MTLCopyAllDevices()
let defaultName = MTLCreateSystemDefaultDevice()?.name ?? "<nil>"
print("all_devices_count=\(all.count)")
print("default=\(defaultName)")'Observed in sandbox:
all_devices_count=0
default=<nil>Then:
python -c 'import mlx.core as mx; print("ok", mx.float32)'Observed in sandbox:
- MLX may abort during Metal init instead of failing gracefully.
Control result in a normal terminal on the same machine:
all_devices_count=1
default=Apple M5
ok mlx.core.float32Expected:
- Either expose Metal consistently, or clearly document that Metal is intentionally unavailable in sandboxed sessions.
What is the expected behavior?
_No response_