I've got userforms in the root directory, run dev/build, and can see the correct items listed in the output (UserDefinedForm etc), but the Forms tab is not appearing in the editor, and old 2.2 forms aren't running. What am I doing wrong?
No you shouldnt need any other files. Check that the page is actually a user defined form type in the pages 'Behaviour' tab. I think it got renamed when it got moved to a module so your page could have reverted to a standard 'Page' type rather then a Form page