diff --git a/plugins/platforms/slack/adapter.py b/plugins/platforms/slack/adapter.py
index 54dd79bb134..4eaacfdbf62 100644
--- a/plugins/platforms/slack/adapter.py
+++ b/plugins/platforms/slack/adapter.py
@@ -10,6 +10,7 @@ Uses slack-bolt (Python) with Socket Mode for:
 
 import asyncio
 import contextvars
+import inspect
 import json
 import logging
 import os
@@ -704,6 +705,31 @@ class SlackAdapter(BasePlatformAdapter):
         # first ping/pong as evidence of a wedged transport.
         self._socket_first_ping_grace_s = 60.0
 
+    async def _close_workspace_clients(self) -> None:
+        """Close any Slack SDK clients that may own aiohttp sessions."""
+        clients: List[Any] = []
+        if self._app is not None:
+            primary_client = getattr(self._app, "client", None)
+            if primary_client is not None:
+                clients.append(primary_client)
+        clients.extend(self._team_clients.values())
+
+        seen_ids: set[int] = set()
+        for client in clients:
+            ident = id(client)
+            if ident in seen_ids:
+                continue
+            seen_ids.add(ident)
+
+            for method_name in ("close", "aclose"):
+                closer = getattr(client, method_name, None)
+                if not callable(closer):
+                    continue
+                result = closer()
+                if inspect.isawaitable(result):
+                    await result
+                break
+
     def _start_socket_mode_handler(self) -> None:
         """Start the Slack Socket Mode background task."""
         if not self._app or not self._app_token:
@@ -1334,6 +1360,7 @@ class SlackAdapter(BasePlatformAdapter):
             # receive every Slack event and dispatch it twice, producing double
             # responses — the same bug that affected DiscordAdapter (#18187).
             await self._stop_socket_mode_handler()
+            await self._close_workspace_clients()
             self._app = None
             self._app_token = app_token
             self._proxy_url = proxy_url
@@ -1651,9 +1678,14 @@ class SlackAdapter(BasePlatformAdapter):
                 )
 
         await self._stop_socket_mode_handler()
+        await self._close_workspace_clients()
         self._app = None
         self._app_token = None
         self._proxy_url = None
+        self._bot_user_id = None
+        self._team_clients = {}
+        self._team_bot_user_ids = {}
+        self._channel_team = {}
 
         self._release_platform_lock()
 
diff --git a/tests/gateway/test_slack.py b/tests/gateway/test_slack.py
index 61fc14512fa..b5946e8b968 100644
--- a/tests/gateway/test_slack.py
+++ b/tests/gateway/test_slack.py
@@ -468,6 +468,7 @@ class TestSlackConnectCleanup:
         )
 
         second_handler = MagicMock()
+        second_handler.close_async = AsyncMock(return_value=None)
         # _start_socket_mode_handler awaits the result of start_async via
         # asyncio.create_task — so the stub must return a real coroutine, not a
         # bare MagicMock.
@@ -490,6 +491,62 @@ class TestSlackConnectCleanup:
         first_handler.close_async.assert_awaited_once_with()
         assert adapter._handler is second_handler
 
+        with patch("gateway.status.release_scoped_lock"):
+            await adapter.disconnect()
+
+    @pytest.mark.asyncio
+    async def test_disconnect_closes_workspace_clients_and_clears_runtime_state(self):
+        """Regression for #51465: shutdown must close Slack WebClients.
+
+        ``hermes gateway run --replace`` takes the old process through the
+        normal adapter.disconnect() path. If Slack leaves AsyncWebClient
+        instances open there, aiohttp logs ``Unclosed client session`` while
+        the old gateway exits after SIGTERM.
+        """
+        config = PlatformConfig(enabled=True, token="xoxb-fake")
+        adapter = SlackAdapter(config)
+
+        socket_task = asyncio.create_task(_pending_for_fake_task())
+        handler = MagicMock()
+        handler.close_async = AsyncMock(return_value=None)
+
+        primary_client = MagicMock()
+        primary_client.close = AsyncMock(return_value=None)
+        team_client = MagicMock()
+        team_client.close = AsyncMock(return_value=None)
+
+        adapter._running = True
+        adapter._handler = handler
+        adapter._socket_mode_task = socket_task
+        adapter._app = MagicMock()
+        adapter._app.client = primary_client
+        adapter._team_clients = {"T_FAKE": team_client}
+        adapter._team_bot_user_ids = {"T_FAKE": "U_BOT"}
+        adapter._channel_team = {"C_FAKE": "T_FAKE"}
+        adapter._platform_lock_scope = "slack-app-token"
+        adapter._platform_lock_identity = "xapp-fake"
+        adapter._app_token = "xapp-fake"
+        adapter._proxy_url = "http://proxy.example.com:3128"
+        adapter._bot_user_id = "U_BOT"
+
+        with patch("gateway.status.release_scoped_lock") as mock_release:
+            await adapter.disconnect()
+
+        handler.close_async.assert_awaited_once_with()
+        primary_client.close.assert_awaited_once_with()
+        team_client.close.assert_awaited_once_with()
+        assert socket_task.cancelled()
+        assert adapter._app is None
+        assert adapter._handler is None
+        assert adapter._socket_mode_task is None
+        assert adapter._team_clients == {}
+        assert adapter._team_bot_user_ids == {}
+        assert adapter._channel_team == {}
+        assert adapter._bot_user_id is None
+        assert adapter._app_token is None
+        assert adapter._proxy_url is None
+        mock_release.assert_called_once_with("slack-app-token", "xapp-fake")
+
 
 # ---------------------------------------------------------------------------
 # TestSlackSocketWatchdog