Codex tip: /fork and /side break your prompt cache — new session_id means new cache key
YouJiacheng · x · 2026-09-11
Developer YouJiacheng warns not to use /fork or /side in Codex: they create a new sessionid, changing the promptcachekey and causing cache misses. The docs explicitly say these features should only be used when you want to prevent a cache hit.
Quoted reply from @KillcoDer adds context: the session ID is the cache key — forks and side chats create a new one, spawning a subagent rewrites history (another miss), and back in May every guardian check also caused a miss. The author has tagged Codex lead thsottiaux asking for a fix.
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