fix: return float timeouts on MCP SDK 2.x in session_context

_read_timeout() documented that MCP SDK 1.x wants a timedelta while 2.x
wants the plain float, but the body always returned timedelta. On mcp 2.x
that value reaches anyio.fail_after(), which adds it to current_time(),
raising TypeError for every session creation (fixes #6938).

Detect the installed SDK major version once (falling back to the current
1.x behavior when detection fails) and pass through float seconds on 2.x.
Regression tests cover both branches and the detection-failure fallback,
independent of the SDK version installed in the test environment.

Author: LUbaoshuai

src/google/adk/tools/mcp_tool/session_context.py

@@ -18,6 +18,9 @@
 from contextlib import AbstractAsyncContextManager
 from contextlib import AsyncExitStack
 from datetime import timedelta
+from functools import lru_cache
+from importlib.metadata import PackageNotFoundError
+from importlib.metadata import version
 import logging
 from types import TracebackType
 from typing import Any
@@ -37,7 +40,21 @@
 _T = TypeVar('_T')
 
 
-def _read_timeout(seconds: Optional[float]) -> Optional[timedelta]:
+@lru_cache(maxsize=1)
+def _mcp_wants_float_timeouts() -> bool:
+  """Whether the installed MCP SDK expects plain seconds as timeouts.
+
+  MCP SDK 1.x requires a ``datetime.timedelta`` for ``read_timeout_seconds``,
+  while 2.x takes the number of seconds as a float. Detection failures fall
+  back to the 1.x behavior, which is what ADK pins today.
+  """
+  try:
+    return int(version('mcp').split('.')[0]) >= 2
+  except (PackageNotFoundError, ValueError, IndexError):
+    return False
+
+
+def _read_timeout(seconds: Optional[float]) -> Optional[float | timedelta]:
   """Converts a timeout in seconds to the type ``ClientSession`` expects.
 
   ADK carries every timeout as float seconds. MCP SDK 1.x wants a
@@ -52,6 +69,8 @@ def _read_timeout(seconds: Optional[float]) -> Optional[timedelta]:
   """
   if seconds is None:
     return None
+  if _mcp_wants_float_timeouts():
+    return float(seconds)
   return timedelta(seconds=seconds)
 
 

tests/unittests/tools/mcp_tool/test_session_context.py

@@ -17,6 +17,7 @@
 import asyncio
 from contextlib import AsyncExitStack
 from datetime import timedelta
+from importlib.metadata import PackageNotFoundError
 import time
 from unittest.mock import AsyncMock
 from unittest.mock import Mock
@@ -25,6 +26,7 @@
 from google.adk.features import FeatureName
 from google.adk.features._feature_registry import temporary_feature_override
 from google.adk.tools.mcp_tool.session_context import _format_exception
+from google.adk.tools.mcp_tool.session_context import _mcp_wants_float_timeouts
 from google.adk.tools.mcp_tool.session_context import _read_timeout
 from google.adk.tools.mcp_tool.session_context import SessionContext
 import httpx
@@ -1013,13 +1015,44 @@ class TestReadTimeout:
   """ADK carries timeouts as float seconds and converts at the SDK boundary."""
 
   def test_none_stays_none(self):
-    assert _read_timeout(None) is None
+    with patch(
+        'google.adk.tools.mcp_tool.session_context._mcp_wants_float_timeouts',
+        return_value=False,
+    ):
+      assert _read_timeout(None) is None
+    with patch(
+        'google.adk.tools.mcp_tool.session_context._mcp_wants_float_timeouts',
+        return_value=True,
+    ):
+      assert _read_timeout(None) is None
 
-  def test_seconds_become_the_type_the_sdk_wants(self):
-    assert _read_timeout(30) == timedelta(seconds=30)
+  def test_mcp_1x_seconds_become_a_timedelta(self):
+    with patch(
+        'google.adk.tools.mcp_tool.session_context._mcp_wants_float_timeouts',
+        return_value=False,
+    ):
+      assert _read_timeout(30) == timedelta(seconds=30)
+      assert _read_timeout(0) == timedelta(seconds=0)
+      assert _read_timeout(0.5) == timedelta(seconds=0.5)
 
-  def test_zero_is_a_real_timeout_not_a_missing_one(self):
-    assert _read_timeout(0) == timedelta(seconds=0)
+  def test_mcp_2x_seconds_stay_seconds(self):
+    with patch(
+        'google.adk.tools.mcp_tool.session_context._mcp_wants_float_timeouts',
+        return_value=True,
+    ):
+      assert _read_timeout(30) == 30
+      assert _read_timeout(0) == 0
+      assert _read_timeout(0.5) == 0.5
+      assert isinstance(_read_timeout(30), float)
 
-  def test_fractional_seconds_survive(self):
-    assert _read_timeout(0.5) == timedelta(seconds=0.5)
+  def test_detection_failure_falls_back_to_timedelta(self):
+    with patch(
+        'google.adk.tools.mcp_tool.session_context.version',
+        side_effect=PackageNotFoundError('mcp'),
+    ):
+      _mcp_wants_float_timeouts.cache_clear()
+      try:
+        assert _mcp_wants_float_timeouts() is False
+        assert _read_timeout(30) == timedelta(seconds=30)
+      finally:
+        _mcp_wants_float_timeouts.cache_clear()