We serve repositories from multiple URLs: https://git..../reponame and https://git..../ro/reponame. Each of these has a different purpose. The first is the main URI, the second is a read only replica which doesn't require kerberos authentication. We're also considering some other special prefixes (/backdoor/, etc.). For a variety of reasons we can not serve the read/write version to phabricator (as an externally hosted repo). This means that repository auto-detection doesn't work.
The remote URI for this working copy is "https://git.../reponame". No repositories matched the query. Check that your configuration is correct, or use "repository.callsign" to select a repository explicitly.
Since we may many hundreds of repositories manually adding a .arcconfig to each one is time consuming an expensive. We have managed to eliminate the need for phabricator.uri and base by setting them in /etc/arcconfig. Obviously for callsigns this approach won't work. We'd like to be able to list server-set a set of alternate URIs that map the same repository.
This is also useful if a repo gets renamed or moved to a different host.