Function start 

pub fn start() -> Result<(), RegistryCacheError>

Spawns the host-side zot process using the previously persisted config at paths::config_path. Returns Ok(()) immediately if zot is already running. Does not touch refs – this is a process-level operation, not a profile lifecycle event.

Use this from caproni registry start for explicit recovery after zot has died (crash, OOM, user kill). For normal lifecycle, use ensure.

Errors

• RegistryCacheError::ZotNotInstalled if zot is not on PATH.
• RegistryCacheError::NoPersistedConfig if no ensure has ever run for this user.