Memoir hugely simplified my own work in LaTeX back when I was doing book composition.
Or, just use LyX....
What I want is something like npm-like package management for this, where the packages are just kept there next to the document. I don't care if I'll have a package 20 times on my system either, storage hasn't been a concern in many years.
I'm using LaTeX 2e for 25+ years. This has literally never happened to me. If that's not stability, I don't know what is. LaTeX documents I wrote in my grad days still compile for me. I just checked and it does. I do keep the dependency packages myself in my folder.
Has this issue ever happened to anyone? Why would LaTeX distribution getting updated break my documents? It's still the same latex compiler and the same base styles and packages!
it gets annoying when you use LaTeX once a year for 25 years.
That's me.
Is there any specific issue you face which stops you from compiling old files?
As I mentioned in my other comment, my grad school days documents are still compiling fine.
If you still use LaTeX 2e and you've got all the dependency packages with you, pdflatex should Just Work. right? I can't remember any major change that would outright break your compilation. And I haven't seen such issue too myself. So I genuinely want to know what specific issues you or others face that wouldn't even let you compile your document.
My next step was to just try doing the build in containers but I even ran into it there once because I accidentally pulled a newer image...
But it's just anecdotally. Maybe I really was holding it all wrong.
Ironically, very similar to the story with modern C++. If you use a limited subset it can "just work" but only if you are disciplined and don't have to mix in legacy code that's pre-C++11.