mountOf
Who a name's mount is, if an app showing the forge's pages knows (the registry: a mirrored release's or codebase's, by its author and name): the mount, what to call it and its page, and which of the app's tabs it's under. Crumbs show it as one crumb, standing for the names up to the mount. Set once, as that app's pages start.
export const mountOf: { current?: ( name: string, ) => { mount: string; label: string; href: string; tab: string } | undefined; } = {}