Sounds like you might be looking for a Static Site Generator. Astro was already mentioned. There's plenty of others, mostly geared towards blogs. I also had success with docfx and MkDocs, both for project documentation.
Yep. I'm well versed with static site generators but every one I've ever worked with has been heavily template based rather than being an actual layout engine that map onto HTML+CSS+SVG. i.e. They all require you to still write in HTML+CSS+SVG rather than being a generalised way of writing HTML+CSS+SVG without dealing with the warts of those languages.
I don't entirely get what you mean by "layout engine". A WYSIWYG editor perhaps? Or maybe a canvas like Microsoft OneNote, where you can draw and put text boxes? Or a word processor? Why isn't the usual Markdown (or the like) approach enough?
My gut feeling is that you cannot (fully) abstract away HTML/CSS if you want the result to feel like an actual website.
With Astro, MkDocs or docfx, I do not have to touch HTML, except maybe for creating the master layout and/or transformation rules, if needed.
> Why isn't the usual Markdown (or the like) approach enough?
Because you can't use markdown to design CSS or SVG animations. I want to be able to design an animation with code that describes how the elements move/interact and then compile that down into CSS or SVG keyframes so that I don't have to manually declare however many arbitrarily complex keyframes.
I understand the purpose of a static site generator and I'm not looking for anything to replace that. Rather I want to be able to write the templates for my static sites without 1. writing exceptionally tedious HTML & CSS and without 2. relying on client side JS to do those tedious things.
I think HTML+CSS is already a pretty good layout engine, so people don't really bother. In fact I think it's so good it's used even when it really shouldn't be, like with Electron applications.
