Function codex_home_dir 

pub fn codex_home_dir(root: &Path, project: &str, agent: &str) -> PathBuf

Absolute path to the per-agent Codex home directory. CODEX_HOME relocates codex’s entire state root — config, sessions, history — so pointing each codex agent at its own rendered home is the clean per-process isolation mechanism: MCP tables and instructions can’t collide across agents. render writes <this>/config.toml; the wrapper exports CODEX_HOME=<this> and symlinks the operator’s auth.json in so agents share the existing login.