Follow-ups from sweeper review of #43763:
- tests/docker/test_tini_compat_shim.py asserts the dispatcher
ENTRYPOINT (with /init delegation check) instead of a bare /init
- tests/docker/test_smoke.py gains a docker run --init regression
for the non-PID-1 fallback (#38349)
- website/docs/user-guide/docker.md and the s6 supervision skill
document the dispatcher and its wrapped-runtime fallback