diff --git a/agent-cmd.sh b/agent-cmd.sh
index cc317c0..fab0aab 100755
--- a/agent-cmd.sh
+++ b/agent-cmd.sh
@@ -27,9 +27,19 @@ fi
 # Brief delay to let tmux update pane status
 sleep 0.1
 
-# Count panes still running (pane_dead=0)
-# Note: our own pane counts as running since this script is executing
-running=$(tmux list-panes -F '#{pane_dead}' | grep -c '^0$' || true)
+window_id=$(tmux display-message -p '#{window_id}')
+my_pane=$(tmux display-message -p '#{pane_id}')
 
-# If we're the only pane still running, all others are dead - detach
-[ "$running" -le 1 ] && tmux detach-client
+# Count live sibling panes (not us, not dead)
+other_live=$(tmux list-panes -t "$window_id" -F '#{pane_id} #{pane_dead}' \
+  | awk -v me="$my_pane" '$1 != me && $2 == "0"' | wc -l | tr -d ' ')
+
+if [ "$other_live" -eq 0 ]; then
+  # No live siblings — close the popup and kill the window
+  # (also cleans up any dead siblings).
+  tmux detach-client
+  tmux kill-window -t "$window_id" 2>/dev/null || true
+else
+  # User has split off other live panes — only kill ours, keep popup open.
+  tmux kill-pane 2>/dev/null || true
+fi