Support bounded machine instruction step counts in MCP

tests/sdbg/test_mcp_adapter.py

@@ -55,6 +55,16 @@ class McpAdapterTests(unittest.TestCase):
             self.client.step_source('back')
         self.assertEqual(len(self.calls), before)
 
+    def test_machine_step_count_is_validated_before_rpc(self):
+        before = len(self.calls)
+        for count in (0, 65, True):
+            with self.assertRaisesRegex(SessionError, '1..64'):
+                self.client.step_instruction(count)
+        self.assertEqual(len(self.calls), before)
+        self.client.step_instruction(3)
+        self.assertEqual(self.calls[-1][1], 'step')
+        self.assertEqual(self.calls[-1][2]['count'], 3)
+
     def test_press_key_releases_shift_after_snapshot_error(self):
         calls = []