diff --git a/gateway/run.py b/gateway/run.py
index dcee18e51..d3f1eddbf 100644
--- a/gateway/run.py
+++ b/gateway/run.py
@@ -1756,6 +1756,31 @@ class GatewayRunner:
                 pass
             self._cleanup_agent_resources(agent)
 
+    def _finalize_shutdown_cached_agents(self, active_agents: Dict[str, Any]) -> None:
+        """Hard-clean idle cached agents during full gateway shutdown.
+
+        Normal cache eviction uses release_clients() so a session can resume
+        with preserved tool state. Full gateway shutdown is a real session
+        boundary, so cached agents must be torn down like active ones.
+        """
+        _cache = getattr(self, "_agent_cache", None)
+        _lock = getattr(self, "_agent_cache_lock", None)
+        if _cache is None or _lock is None:
+            return
+
+        active_ids = {id(agent) for agent in active_agents.values()}
+        cached_agents: List[Any] = []
+        with _lock:
+            for entry in list(_cache.values()):
+                agent = entry[0] if isinstance(entry, tuple) and entry else None
+                if agent is None or id(agent) in active_ids:
+                    continue
+                cached_agents.append(agent)
+            _cache.clear()
+
+        for agent in cached_agents:
+            self._cleanup_agent_resources(agent)
+
     def _cleanup_agent_resources(self, agent: Any) -> None:
         """Best-effort cleanup for temporary or cached agent instances."""
         if agent is None:
@@ -2628,6 +2653,7 @@ class GatewayRunner:
                     logger.error("Failed to launch detached gateway restart: %s", e)
 
             self._finalize_shutdown_agents(active_agents)
+            self._finalize_shutdown_cached_agents(active_agents)
 
             for platform, adapter in list(self.adapters.items()):
                 try:
diff --git a/tests/gateway/test_gateway_shutdown.py b/tests/gateway/test_gateway_shutdown.py
index 4dc9919bc..3e797130e 100644
--- a/tests/gateway/test_gateway_shutdown.py
+++ b/tests/gateway/test_gateway_shutdown.py
@@ -1,4 +1,6 @@
 import asyncio
+import threading
+from collections import OrderedDict
 from unittest.mock import AsyncMock, MagicMock, patch
 
 import pytest
@@ -125,6 +127,28 @@ async def test_gateway_stop_service_restart_sets_named_exit_code():
     assert runner._exit_code == GATEWAY_SERVICE_RESTART_EXIT_CODE
 
 
+@pytest.mark.asyncio
+async def test_gateway_stop_hard_cleans_cached_agents():
+    runner, adapter = make_restart_runner()
+    adapter.disconnect = AsyncMock()
+    runner._agent_cache = OrderedDict()
+    runner._agent_cache_lock = threading.Lock()
+    runner._cleanup_agent_resources = MagicMock()
+
+    cached_a = MagicMock()
+    cached_b = MagicMock()
+    runner._agent_cache["session-a"] = (cached_a, "sig-a")
+    runner._agent_cache["session-b"] = (cached_b, "sig-b")
+
+    with patch("gateway.status.remove_pid_file"), patch("gateway.status.write_runtime_status"):
+        await runner.stop()
+
+    assert list(runner._agent_cache.keys()) == []
+    runner._cleanup_agent_resources.assert_any_call(cached_a)
+    runner._cleanup_agent_resources.assert_any_call(cached_b)
+    assert runner._cleanup_agent_resources.call_count == 2
+
+
 @pytest.mark.asyncio
 async def test_drain_active_agents_throttles_status_updates():
     runner, _adapter = make_restart_runner()