Why no GitHub?

Claude 4.5 Sonnet definitely struggles with Swift 6.2 Concurrency semantics and has several times gotten itself stuck rather badly. Additionally Claude Code has developed a number of bugs, including rapidly re-scrolling the terminal buffer, pegging local CPU to 100%, and consuming vast amounts of RAM. Codex CLI was woefully behind a few months ago and, despite overly conservative out-of-the-box sandbox settings, has quite caught up to Claude Code. (Gemini CLI is an altogether embarrassing experience, but Google did just put a solid PM behind it and 3.0 Pro should be out this month if we're lucky.)

Codex with 5.1 high managed to thoughtfully paw through the documentation and source code and - with a little help pulling down parts of the Swift Book - managed to correctly resolve the issue.

I remember getting the thread manager right being one of the harder parts of my operating systems course doing an undergrad in computer science; testing threaded programs has always been a challenge. It's a strange circle-of-life moment to realize that what was hard for undergrads also serves as a benchmark for coding agents!