feat: add session-scoped client tool waits

backend/tests/test_tool_policy.py

@@ -32,6 +32,10 @@ class ToolPolicyTests(unittest.TestCase):
             policy_for_tool(runtime_tool("client")).execution_mode,
             "async",
         )
+        self.assertEqual(
+            policy_for_tool(runtime_tool("client")).response_wait_mode,
+            "timeout",
+        )
 
     def test_explicit_policy_is_normalized(self):
         policy = policy_for_tool(
@@ -41,12 +45,14 @@ class ToolPolicyTests(unittest.TestCase):
                     "allow_interruptions": False,
                     "execution_mode": "immediate",
                     "wait_for_response": False,
+                    "response_wait_mode": "session",
                 },
             )
         )
         self.assertFalse(policy.allow_interruptions)
         self.assertTrue(policy.cancel_on_interruption)
         self.assertFalse(policy.wait_for_response)
+        self.assertEqual(policy.response_wait_mode, "session")
 
 
 class ToolInterruptionStrategyTests(unittest.IsolatedAsyncioTestCase):