diff --git a/lib/agent-session.sh b/lib/agent-session.sh
index ffd71b1..269e94a 100644
--- a/lib/agent-session.sh
+++ b/lib/agent-session.sh
@@ -399,6 +399,7 @@ monitor_phase_loop() {
     # shellcheck disable=SC2034  # read by phase-handler.sh callback
     LAST_PHASE_MTIME="$phase_mtime"
     idle_elapsed=0
+    idle_pane_count=0
 
     # Terminal phases
     case "$current_phase" in