Function memory_command 

pub fn memory_command(arg: &str, runtime: &Runtime) -> CommandResult

/memory on|recall|capture|once|status|off|index-history|why (task A5, spec §7.3): the ONE deterministic engine entry point every frontend — TUI, headless chat, RPC, server, watcher, agent — shares via handle_engine_command. Frontends must not duplicate lease or budget logic.

Every enabling arm mints host-owned crate::runtime::memory_context::UserIntentProof::ExplicitCommand proof right here: a deterministic slash command is authoritative (spec assumption 5), and proof never derives from model text.