It is not, Hanami is a batteries-included framework. It not even a pay-as-you-go framework like Pyramid. The equivalent of Flask in Ruby land is Roda+Sequel.
It is likely you use Chrome or a browser that uses Blink for its engine and the OP uses a non-blink browser like Firefox. I use Firefox and I can cofirm since the last few months Youtube usability borders on usable
wmii[0], it implements the acme window layout. But the interesting part is that it exposes its state as a file-system. The main loop is a shell script[1]. So BYO posible, fe here is a Ruby one [2]
Instead of checking wikipedia for a general definition of idempotency, check the RFC for the definition that applies to HTTP
9.1.2 Idempotent Methods
Methods can also have the property of "idempotence" in that (aside
from error or expiration issues) the side-effects of N > 0 identical
requests is the same as for a single request.
As far as dash.el goes, I find lispm's critique of dash.el pretty convincing[0]. However a more profilic emacs coder fried of mine is undeterred and keeps using modern emacs lisp. I think much of the community does as well.