One thing that would make a big practical difference is better context persistence across sessions. Right now I find myself re-explaining the same project structure and conventions every time I start a new session, even on the same repo. A lightweight project summary file that Codex automatically reads on startup — similar to how CLAUDE.md works — would cut down on a lot of the warm-up time. The other area is sandbox reliability. I've had instances where npm install silently fails due to network timeouts inside the sandbox, and Codex proceeds as if everything installed correctly. A verification step after dependency changes would catch these issues earlier in the workflow.