Constant HISTORY_SEARCH_NEEDS_IDENTITY 

const HISTORY_SEARCH_NEEDS_IDENTITY: &str = "history.search: this request carries no agent identity \
     (X-Agent-Token), so whose history to search is unknown. Every agent AgentMux spawns carries \
     one; a process started some other way, or an agent from before identity tokens, must be \
     reopened from AgentMux.";

SearchHistory’s answer to a request that carries no per-agent token.