wiki: Dingtian relay decision, HTTP-over-MQTT, unmanned direction

- dingtian-relay: relay+input controller (4ch on hand). Inputs are decoupled
  from relays (configurable via input_link_relay) — solves the
  access-controller-button-flow blocker the UHPPOTE couldn't. Full protocol from
  the SDK (UDP string control :60001, `00` status parse, input_link_url push,
  multicast discovery). Driver + hardware test still to build.
- dingtian-vs-mqtt: use direct HTTP/UDP now; MQTT skipped (broker = extra infra
  + failure mode + overkill at one-host/few-devices scale) but kept for later
  multi-lane scale.
- autonomous-direction: record the roadmap to fully unmanned (no booth) and how
  it reshapes the threat model (operator-fraud -> unattended-machine threats),
  makes host-in-the-loop entry mandatory, and raises fail-state stakes.
- threat-model: note the unmanned shift. index + log.

gitignore the vendor SDK (dingtian/, 71MB of binaries/examples) — reference
only, protocol captured in the wiki.

wiki/log.md

@@ -94,3 +94,14 @@ earlier "broadcast permission (EACCES)" note in [[device-discovery]] — the rea
 cause was the lib not enabling SO_BROADCAST for the global 255.255.255.255;
 documented the three verified broadcast gotchas + serialization. Added a `reference`
 page type to the schema; new "Dev environment" index section.
+
+## [2026-06-15] decision | Dingtian relay chosen; HTTP over MQTT; unmanned direction
+New relay+input controller on hand (Dingtian 4ch). Its inputs are decoupled from
+relays (configurable via input_link_relay) — solves the [[access-controller-button-flow]]
+blocker the UHPPOTE couldn't. Transport decision [[dingtian-vs-mqtt]]: direct
+HTTP/UDP now (UDP string for relay control on :60001; device input_link_url HTTP
+push for button events), MQTT skipped (broker = infra + failure mode + overkill at
+this scale) but kept for later multi-lane scale. Recorded the stated roadmap to
+**fully unmanned, no-booth** operation in [[autonomous-direction]] and its threat-model
+shift (operator-fraud → unattended-machine threats). New stub [[dingtian-relay]]
+with the full protocol from the SDK. Driver + on-hardware test still to build.