chat: fix use-after-free in invite_candidates trampoline + accept JOIN_INFO_RESP/READY/ERROR for unknown channels

tools/chatgui/stress_restart.sh

@@ -0,0 +1,15 @@
+#!/bin/bash
+set -u
+cd "$(dirname "$0")/build" || exit 1
+export DISPLAY="${DISPLAY:-:0}"
+
+rnd() { local m=$((200 + RANDOM % 2801)) f; printf -v f '%03d' $((m%1000)); sleep "$((m/1000)).$f"; }
+
+while :; do
+    env DISPLAY="$DISPLAY" QT_ACCESSIBILITY=1 ./vibechat >/dev/null 2>&1 &
+    p=$!
+    rnd
+    (( RANDOM % 2 )) && kill -9 "$p" || kill -HUP "$p"
+    wait "$p" 2>/dev/null
+    rnd
+done