static LOCAL_AUTH_KEY: OnceLock<String>Expand description
Process-wide auth key for the local AgentMux instance.
Initialised once by main.rs after Config::from_env_and_args reads
AGENTMUX_AUTH_KEY and removes it from the env. The registry write
path reads this to populate AgentEntry::auth_key, which lets peers
authenticate cross-instance inject forwards.
Tests and the register HTTP handler (which has state.auth_key)
can both pre-set this safely — the first set wins.