I am flabergasted and livid that I cannot actually use this application, as I cannot access my documents.
My fault for not looking more closely before spending my $4.99, but lack of support for such a fundamental and necessary feature in what appears to be an advanced powertool for text editing is pretty mindblowing.
Oh well, back to iA Writer, which is excellent but does not have the taskpaper or automation hooks that I was looking for.
Editing to add: Since this is basically a feature request, I should be clear that the support we need is iCloud Drive and Open in Place, as described at https://developer.apple.com/document-based-apps/ .