diff --git a/docs/ARCHITECTURE.md b/docs/ARCHITECTURE.md
index c9e5889..a411352 100644
--- a/docs/ARCHITECTURE.md
+++ b/docs/ARCHITECTURE.md
@@ -155,7 +155,8 @@ change. Design for it as normal operation. Requirements, not yet implemented:
 - **Failure detection on the Orin.** An app-level heartbeat with a timeout of a
   few seconds, not TCP alone. A connection on a link that went down can stay
   half-open long after the app has re-dialled. Reap dead connections and their
-  per-client queues promptly.
+  per-client queues promptly. Link state doesn't help either: when PD is plugged back
+  in, the Orin's interface stays up while the tablet goes silent for ~5 s.
 - **Downstream (latest-wins):** unchanged. On reconnect, push current state; no
   resend, since stale samples are worthless.
 - **Reliable channel (TTS chunks, acknowledgements):** pending items survive a