As of d9920a7 bundle exec rake warclight:server yields:

RSolr::Error::Http - 400 Bad Request Error: {"responseHeader":{"status":400,"QTime":3,"params":{"facet.query":["pub_date:[2012 TO *]","pub_date:[2007 TO *]","pub_date:[1992 TO *]"],"f.subject_topic_facet.facet.limit":"21","facet.field":["format","{!ex=pub_date_single}pub_date","subject_topic_facet","language_facet","lc_1letter_facet","subject_geo_facet","subject_era_facet"],"facet.pivot":"format,language_facet","sort":"score desc, pub_date_sort desc, title_sort asc","rows":"10","facet":"true","wt":"json","f.language_facet.facet.limit":"11"}},"error":{"metadata":["error-class","org.apache.solr.common.SolrException","root-error-class","org.apache.solr.common.SolrException"],"msg":"sort param field can't be found: pub_date_sort","code":400}} URI: http://127.0.0.1:8983/solr/blacklight-core/select?wt=json&facet.field=format&facet.field=%7B%21ex%3Dpub_date_single%7Dpub_date&facet.field=subject_topic_facet&facet.field=language_facet&facet.field=lc_1letter_facet&facet.field=subject_geo_facet&facet.field=subject_era_facet&facet.query=pub_date%3A%5B2012+TO+*%5D&facet.query=pub_date%3A%5B2007+TO+*%5D&facet.query=pub_date%3A%5B1992+TO+*%5D&facet.pivot=format%2Clanguage_facet&&&rows=10&facet=true&f.subject_topic_facet.facet.limit=21&f.language_facet.facet.limit=11&sort=score+desc%2C+pub_date_sort+desc%2C+title_sort+asc Backtrace: /home/nruest/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/rsolr-2.0.2/lib/rsolr/client.rb:195:in `rescue in execute' /home/nruest/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/rsolr-2.0.2/lib/rsolr/client.rb:185:in `execute' /home/nruest/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/rsolr-2.0.2/lib/rsolr/client.rb:180:in `send_and_receive' /home/nruest/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/bundler/gems/blacklight-8160d7d61143/lib/blacklight/solr/repository.rb:38:in `block in send_and_receive' /home/nruest/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.1.3/lib/active_support/benchmarkable.rb:41:in `block in benchmark' /home/nruest/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.1.3/lib/active_support/core_ext/benchmark.rb:12:in `block in ms' /home/nruest/.rbenv/versions/2.4.0/lib/ruby/2.4.0/benchmark.rb:308:in `realtime' /home/nruest/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.1.3/lib/active_support/core_ext/benchmark.rb:12:in `ms' /home/nruest/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/gems/activesupport-5.1.3/lib/active_support/benchmarkable.rb:41:in `benchmark' /home/nruest/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/bundler/gems/blacklight-8160d7d61143/lib/blacklight/solr/repository.rb:36:in `send_and_receive' /home/nruest/.rbenv/versions/2.4.0/lib/ruby/gems/2.4.0/bundler/gems/blacklight-8160d7d61143/lib/blacklight/solr/repository.rb:22:in `search'

I think it's time to start setting up the default Solr fields for warclight.