Revert the hardcoded 16-job experiment: the combination spec belongs
in scripts/sandbox/generate-e2e-matrix.mjs (restored), not copy-pasted
YAML blocks. What survives from the experiment:
* leg names carry everything - 'os: install -> update (tag -> HEAD)' -
generated per entry, since slash-joined names are all the graph
renders;
* pick-releases annotates each tag ({ref, desktop}) and the generator
threads tag_has_desktop onto windows entries, so the windows run
workflow still gates pre-desktop tags without a probe job;
* the per-OS run workflows are untouched: single job, static 'e2e'
name, native skip gates own all capability knowledge.
install-e2e.yml is one generate job + three per-OS matrix fanouts.
Generator shape (4/16/12 legs for 2 tags), annotation threading, and
all six error paths verified; all four workflows pass actionlint;
driver parses clean pure-ASCII.
1c60bdc30d