* feat(gateway): add loopback locality controls
* fix(gateway): keep loopback auth delays enforced under concurrency
The pending-timer cap let an attacker park cheap failures in every slot and then guess without penalty. Delays now key off a per-key deadline, so parallel guesses wait out the same escalating penalty and are still bounded by the max delay.
* fix(gateway): share one loopback penalty timer per key
Concurrent failures on a key now share a single timer and deadline instead of allocating one per in-flight request. Also corrects the security doc: the delay raises the cost of repeated guessing from one source, but credentials are compared before the failure response is delayed, so it is not a defense against parallel fan-out.
* docs(gateway): record why loopback delay stays post-verification
* docs: refresh generated docs map
* docs: refresh plugin SDK API baseline
* test: update loopback locality CI expectations
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