diff --git a/tools/delegate_tool.py b/tools/delegate_tool.py
index f4da5127a18..2cdce9cae64 100644
--- a/tools/delegate_tool.py
+++ b/tools/delegate_tool.py
@@ -1431,7 +1431,6 @@ def _run_single_child(
                 pass
 
     _heartbeat_thread = threading.Thread(target=_heartbeat_loop, daemon=True)
-    _heartbeat_thread.start()
 
     # Register the live agent in the module-level registry so the TUI can
     # target it by subagent_id (kill, pause, status queries).  Unregistered
@@ -1462,6 +1461,7 @@ def _run_single_child(
         )
 
     try:
+        _heartbeat_thread.start()
         if child_progress_cb:
             try:
                 child_progress_cb("subagent.start", preview=goal)