Function install_plugin_from_source 

pub async fn install_plugin_from_source(
    installer: &dyn PluginInstaller,
    input: PluginSourceInput,
    plugins_root: &Path,
    trust: &PluginTrustConfig,
    disposition: InstallDisposition,
) -> PluginResult<InstalledPlugin>

Stage + install() + commit/rollback, in one call — the seam CLI/HTTP callers should use. See the module docs.