publish-snapshot.sh's header described the silent-truncation failure mode as
the one "this script's own selftest (scenario 8)" reproduces. Wrong twice:
the scenario that reproduces a truncated clone is in
seed-target-dir-selftest.sh, and since #4 split the old scenario 8 into 8a and
8b it is 8b. publish-snapshot-selftest.sh does have a scenario 8 — the
abandoned-marker case — so the pointer landed on a real scenario with a
plausible number that tests something else.
Names the suite as well as the number, and says what the local scenario 8
actually is so the collision cannot re-form.
Closes#6