Going on with this post.
I noticed, again with the help of hyperbolist@#email@example.com, that the startup.rb file can be more simple. I also noticed that the comment I’ve made in the original code was making the thread not going away from the thread list in inbox. So, this one works:
class Redwood::ThreadViewMode @@keymaps[self].add :kill_and_next, "Kill this thread, kill buffer, and view next", '&' def kill_and_next; kill_and_then :next end def kill_and_then op dispatch op do @index_mode.multi_kill [@thread] end end end