The grant is the keystone that makes server->client sends safe: created
only by an authenticated control-plane action, bound at creation to the
session's OBSERVED data-plane source (so it can never be aimed at a third
party), and bounded by bytes, average rate and expiry. Sends stop the
moment the budget runs out, so a buggy action cannot become a flood.
Two granted actions on top of it:
- downtrain: N packets at a given size/interval toward the client, with
seq + send-timestamp in the payload — downstream loss/reorder/jitter,
which an upstream-only train cannot measure.
- big_send: one datagram per requested size, echoing the intended size in
the payload — downstream MTU / black-hole evidence the client cannot
produce for itself (only the far end can emit a large packet toward it).
Tests cover the security properties: no grant without a verified
destination, client requests clamped to server limits, byte budget stops
sending exactly, expiry refuses, and the rate ceiling throttles a burst.
Capabilities gain downtrain + big-send.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
