Tracking: upstream fork improvements to openai/codex-universal

[gerred]

This issue tracks the effort to contribute changes from this fork (Gerred Dillon) back into the upstream openai/codex-universal repository.

What this fork changes

• Improved developer experience and workflow
• Reproducible builds with nix-portable
• Simplified environment setup

Discussion & Updates

• Public discussion & status: X thread
• Feedback and upstreaming progress: Comment here!
• Upstream repo reference: OpenAI/codex-universal

Feel free to use this issue to ask questions, propose collaborations, or track status on PRs merging these updates.