run_circuit_fixture stands up an isolated docker N-hop nested-SSH chain, pipes a
seed-deterministic self-generated payload through it, verifies end-to-end
delivery, captures + checksums a per-hop pcap, emits R3 events, and always tears
the circuit down. Containment is load-bearing: assert_isolated refuses
local/unknown engines up front, every hop is built through the ForwarderPlan
guard, only our own fixture bytes move between our own containers, and the runner
is wired for docker only (multipass e2e refused, not faked). Adds the sor-hop
fixture image (alpine + sshd + tcpdump, lab-relay only) and a docker-gated
acceptance test that skips where no daemon/image is present. Instrument-validation
gate item 1 GREEN: live 3-hop delivery verified, 3 distinct hops, pcaps checksum.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
leetcrypt