script/test-e2e and script/test-e2e-firefox tagged their image with one
fixed name. When two clones ran a suite at once, the second build moved
that tag, the image store deleted the first run's now-untagged image, and
that suite exited 125 without running a test. Each run now tags its image
with the suite's name and twelve random hex digits and runs it by that
tag. The cleanup that runs on exit, Ctrl-C, kill and a closed terminal
removes the run's container if docker's client left it running, then the
image. The image-ID file that guarded against a moving tag is gone.
README.md's End-to-End Tests section says which endings clean up.
Model: opus-5-5
sneak