Function install 

pub fn install(
    archive: &MuragentArchive,
    mur_home: &Path,
    surface: &str,
) -> Result<InstallOutcome, MuragentError>

Install or update a .muragent archive. See module docs for the flow.

mur_home is the root for agent dirs (<mur_home>/agents/<slug>/). The trust store is read and written via TrustStore::load / save, which honour $MUR_HOME independently — callers should either pass the same path the trust store would resolve, or set MUR_HOME consistently.

surface is recorded in the trust entry’s last_seen_surface field. Conventional values: "cli", "hub", "commander".