compliation failure of minimal latex documents

[jack]

Yesterday I did a tlmgr --update, and immediately simple documents broke,
showing the following error:

! LaTeX Error: File `l3backend-pdfmode.def' not found

This error also is spewed for typsetting the simplest latex document I can
imagine: one word in the body, and a preamble consisting of
\documentclass{article} and \begin{document}.

I'm really hoping this is an oversight that's easily fixed in whatever
part of core latex thinks it needs l3backend.  I don't see why a simple
latex document with zero \usepackage calls needs to depend on experimental
latex3 stuff.

Moreover, the `tlmgr info` output for "l3backend" doesn't even tell me
what collection (if any) it belongs to.  It should belong to
collection-latex, though evidently it does not.

Otherwise, even the simplest latex documents would require more than the
"latex fundamental packages" (as the description for collection-latex
reads).

Also, we'd have some package in collection-latex depending on
collection-latexrecommended (I presume).  There's no point to having
collection-latex if you can't do anything without *also* having
collection-latexsomethingelse.

Recently there's been an alarming lack of attention paid to which
collection things wind up in.  I'm thinking specifically of the recent
oberdiek debacle: anything split from oberdiek should have gone in the
same collection that oberdiek was in.  That's because some stuff in
collection-latex depends on oberdiek.  But some of it wound up elsewhere,
including collection-latexextra(!!!).  (That should really be fixed, BTW.)

This meant that upon unexpected compliation failure of non-fancy documents
I had to go hunt for these scattered oberdiek packages one-by-one,
manually, instead of having them automatically updated along with
collection-latex.  That is poor UX.

To be fair, I don't have collection-latexrecommended installed; instead I
have several its packages installed individually.  I try to keep my
installation as trim as possible.  I don't need, and never will need,
e.g., koma-script. Nevertheless, it remains the case that compiling a
minimal latex document shouldn't require latex-recommended.

Either a simple latex document shouldn't depend on l3backend, or l3backend
needs to be in collection-latex.

-jack