Add closing rumor

43.md

@@ -209,3 +209,11 @@ Optionally, the `created_at` of a `kind:416` NIP-59 rumor
 informs the last time an user read DMs from the other participant.
 
 This event should be sent to atleast one of the DM author's NIP-65 `read` relays.
+
+### Chat Session Closing
+
+When removing a not yet expired entry from the "Chat Session List" event,
+a `kind:417` NIP-59 rumor may be used to inform the other participant to
+clear the `<session-privkey>` value from their own entry.
+
+This event should be sent to atleast one of the peer's NIP-65 `read` relays.