beta5: real TCP mode for mlvpnd self-test --tunnel --protocol tcp|udp (tcp default), giving throughput/retransmit numbers directly comparable to iperf3 instead of the old raw-UDP mode's loss-blind numbers. Upload-leg retransmits are real, sender-measured; download-leg retransmits are honestly reported as unavailable rather than a wrong number. docs/superpowers/specs/2026-09-16-tcp-tunnel-self-test-design.md docs/superpowers/plans/2026-09-16-tcp-tunnel-self-test.md