Turns out our presently-undocumented Git Integration fails if you've configured an absolute drupal_basepath.
The code here expects it to be relative:
# Clone repos if necessary
drupal_sites.each do |name, site|
if site.has_key?("git_url") && site.has_key?("git_dir") && !Dir.exists?( Dir.pwd + "/" + drupal_basepath + "/" + site['git_dir'] + "/.git")
puts "No Git Clone found for \"#{name}\""
git_cmd = "git clone #{site['git_url']} #{drupal_basepath}/#{site['git_dir']}"
%x{ #{git_cmd} }
end
end
So . . don't do that.