perf(utils): cache find_context_parameter introspection

Adds @functools.lru_cache to find_context_parameter so the inspect.signature
+ typing.get_type_hints lookup runs once per function, not on every MCP
confirmation callback or declaration build. No public surface change.

Co-authored-by: George Weale <gweale@google.com>
PiperOrigin-RevId: 916204929

Author: GWeale

src/google/adk/utils/context_utils.py

@@ -21,6 +21,7 @@
 from __future__ import annotations
 
 from contextlib import aclosing
+import functools
 import inspect
 import typing
 from typing import Any
@@ -62,6 +63,7 @@ def _is_context_type(annotation: Any) -> bool:
   return annotation is Context
 
 
+@functools.lru_cache(maxsize=1024)
 def find_context_parameter(func: Callable[..., Any]) -> str | None:
   """Find the parameter name that has a Context type annotation.
 

tests/unittests/utils/test_context_utils.py

@@ -15,10 +15,12 @@
 """Tests for context_utils module."""
 
 from typing import Optional
+from unittest import mock
 
 from google.adk.agents.callback_context import CallbackContext
 from google.adk.agents.context import Context
 from google.adk.tools.tool_context import ToolContext
+from google.adk.utils import context_utils
 from google.adk.utils.context_utils import find_context_parameter
 
 
@@ -129,3 +131,25 @@ def my_tool(
       return query
 
     assert find_context_parameter(my_tool) == 'ctx'
+
+
+class TestFindContextParameterCaching:
+  """Tests for find_context_parameter caching behavior."""
+
+  def test_repeated_calls_inspect_signature_once(self):
+    """Repeated calls with the same function reuse the cached result."""
+
+    def my_tool(ctx: Context) -> str:
+      return 'ok'
+
+    find_context_parameter.cache_clear()
+
+    with mock.patch.object(
+        context_utils.inspect,
+        'signature',
+        wraps=context_utils.inspect.signature,
+    ) as spy:
+      for _ in range(10):
+        assert find_context_parameter(my_tool) == 'ctx'
+
+    assert spy.call_count == 1