feat(session): add explicit leave and immediate slot release

docs/M016_LATENCY_PROCEDURE.md

@@ -14,6 +14,7 @@ browser timestamp from an ESP timestamp.
 | command to painted view | browser | `move` send to next frame after matching view render |
 | handler and send | ESP | existing `/diagnostics` maxima |
 | network round trip | client | ICMP and WebSocket heartbeat samples |
+| ESP heartbeat handling | ESP | bounded acknowledgement preparation interval |
 
 The accepted command acknowledgement contains the authoritative `stateSequence`.
 The browser records a sample only after the complete view with that sequence is
@@ -38,6 +39,10 @@ rendered and the next animation frame occurs. Samples are local-only, capped at
    and send maxima, queue high-water marks, observer view chunk count, and
    ICMP/WebSocket round trips. Attribute a delay only when the matching
    interval is elevated.
+7. For the compact quality indicator, record the rounded `Отклик`, `Связь`,
+   and `ESP` values after the five-second heartbeat cadence has collected a
+   fresh sample. `Связь` is the non-negative round-trip remainder, not a pure
+   Wi-Fi measurement.
 
 ## Safety checks