fix(gateway): move quick-command dispatch before built-in handlers

Quick commands of type "alias" that target built-in slash commands
(e.g. /h -> /model) were processed too late in _handle_message — after
the if-canonical=="model" checks. This meant alias expansion never
reached the target handler and fell through to the LLM as raw text.

Two fixes:
1. Move the quick_commands block before built-in dispatch so alias
   targets (like /model) hit the correct handler after expansion.
2. Extract bare command name from target_command via .split()[0] to
   feed _resolve_cmd() correctly (was using the full arg-string).

tests/e2e/test_platform_commands.py

@@ -138,6 +138,29 @@ class TestSlashCommands:
         response_text = send.call_args[1].get("content") or send.call_args[0][1]
         assert "compress" in response_text.lower() or "context" in response_text.lower()
 
+    @pytest.mark.asyncio
+    async def test_quick_command_alias_targets_builtin_command_with_args(
+        self, adapter, runner, platform
+    ):
+        """Alias targets with args must reach the built-in command handler."""
+        runner.config.quick_commands = {
+            "s": {"type": "alias", "target": "/status extra-arg"}
+        }
+        async def _handle_status(event):
+            assert event.get_command_args() == "extra-arg"
+            return "status via alias"
+
+        runner._handle_status_command = AsyncMock(side_effect=_handle_status)
+
+        send = await send_and_capture(adapter, "/s", platform)
+
+        send.assert_called_once()
+        response_text = send.call_args[1].get("content") or send.call_args[0][1]
+        assert response_text == "status via alias"
+        runner._handle_status_command.assert_awaited_once()
+        runner._handle_message_with_agent.assert_not_awaited()
+
+
 
 class TestSessionLifecycle:
     """Verify session state changes across command sequences."""