Currently it is not possible to access the repository root address in browser, i.e., [SCM_URL]/hg in browser. The reason is that SCM-manager always assumes that the concrete repo name is present in the URL. It is checked in DefaultRepositoryManager.getFromTypeAndUri and if empty then IllegalStateException is thrown. Full stack trace is attached.
Is it possible to show something more friendly if a user goes to the root address? Some possible solutions: