diff --git a/src/daemon/spawner.py b/src/daemon/spawner.py
index 3ac998b..87c7cf4 100644
--- a/src/daemon/spawner.py
+++ b/src/daemon/spawner.py
@@ -360,6 +360,21 @@ curl -X POST http://{self.api_host}:{self.api_port}/api/projects/{project_id}/ta
                 raise AgentBusyError(agent_id)
             await self.counter.acquire(agent_id)
 
+        # ── v2.7.2: session state 检查（防外部占用）──
+        if use_main_session:
+            session_state = self._check_session_state(agent_id)
+            if session_state.get("lock_pid_alive"):
+                # main session 被 webchat/Control UI/cron 占用
+                logger.info("Spawn skipped: %s main session locked by PID %d",
+                            agent_id, session_state.get("lock_pid"))
+                raise AgentBusyError(f"{agent_id}: session locked by PID {session_state.get('lock_pid')}")
+            if session_state.get("status") == "processing":
+                logger.info("Spawn skipped: %s main session processing", agent_id)
+                raise AgentBusyError(f"{agent_id}: session processing")
+            if session_state.get("recent_compact"):
+                logger.info("Spawn skipped: %s compacting", agent_id)
+                raise AgentBusyError(f"{agent_id}: compacting")
+
         # Session 策略：main > reuse > new
         if use_main_session:
             session_id = None