diff --git a/docs/BOUNDARY.md b/docs/BOUNDARY.md
index 77fd13e..a97d0ba 100644
--- a/docs/BOUNDARY.md
+++ b/docs/BOUNDARY.md
@@ -12,6 +12,11 @@ One WebSocket, `ws://<orin>:7700/`, JSON text messages, each with a `"t"` type.
 The tablet reaches the car Orin at `192.168.55.1` over USB NCM; the app binds to
 that network itself (see `app-flutter`'s initial plan).
 
+svc-gw caps its socket's send rate (`SO_MAX_PACING_RATE`, ~5 MB/s; project-yukart
+decision 28, proposed). Unpaced bursts toward the tablet stall the USB link for
+seconds; paced traffic does not (app-flutter `docs/impl/reports/LINK-TEST-2026-10-11.md`).
+State messages are far below the cap; it matters for utterances and anything bulky.
+
 The client always connects and owns reconnection. svc-gw refuses peers outside
 loopback, RFC 1918 and the tailnet's 100.64.0.0/10.