Had the similar experience, and as it happens, I was also looking to build something with Elixir/Phoenix backend.. Its nice that it comes with a proxy `fetch`

Had the similar experience, and as it happens, I was also looking to build something with Elixir/Phoenix backend.. Its nice that it comes with a proxy `fetch` implementation that you can use to make requests to your API backend from the svelekit "backend", but there are many leaky API surfaces around it, esp when dealing with cookies. The docs is also rather lacking regarding the many callbacks that can run on both server/client, though it is somewhat understandable given everything is still very much in flux...