[tlbuild] report on building locally on an old macos and a query

[Karl Berry]

    fmtutil [ERROR]: not building etex due to missing engine: pdftex

Strange. That error message comes from this code in fmtutil.pl:

  if (!TeXLive::TLUtils::which($eng)) {
    ...
      print_deferred_error("not building $fmt due to missing engine: $eng\n");
      return $FMT_FAILURE;

where our which() function in TLUtils.pm simply iterates through each
$dir of $PATH checking for -x $dir/$eng, if you see what I mean.
So it's puzzling that I don't work.

If you add --no-error-if-no-engine=pdftex to the fmtutil command line,
what happens? Then it should go ahead and try to run pdftex anyway.
Would be interesting to see if it succeeds or fails.

    perhaps the time with seconds of production is therein?

Yes, .fmt files include a timestamp. With minute resolution, as I
recall.  Not sure. If you use the SOURCE_DATE_EPOCH envvar, possibly
with FORCE_SOURCE_DATE=1, you should be able to control the time used.
See the pdftex manual. We created these envvars so reproducible builds
(of documents, not formats, but the same should apply) would be possible.

HTH,
karl