perf(prebuilt): cache _get_all_injected_args by tool object identity

`_get_all_injected_args` runs `get_input_schema()`, `get_type_hints`,
and `inspect.signature` on every tool for every `ToolNode` construction.
When the same tool objects are passed to repeated `create_agent` calls
(the common case), this work was repeated from scratch each time.

Add a module-level cache keyed by `id(tool)`. The cache entry stores a
strong reference to the tool alongside the result, which prevents GC
from reusing the id for a different object and making an incorrect cache
hit. The `entry[0] is tool` identity check provides a second safety
guard.

`BaseTool` (Pydantic v2 BaseModel) is not hashable, so `@lru_cache`
cannot be used directly — hence the id-based dict approach.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

libs/prebuilt/langgraph/prebuilt/tool_node.py

@@ -40,6 +40,7 @@ Typical Usage:
 from __future__ import annotations
 
 import asyncio
+import functools
 import inspect
 import json
 from collections.abc import Awaitable, Callable
@@ -1842,9 +1843,17 @@ def _get_injection_from_type(
     return None
 
 
+# Cache keyed by tool object identity. Stores (tool, result) to keep a strong
+# reference that prevents GC from reusing the id for a different object.
+_INJECTED_ARGS_CACHE: dict[int, tuple[BaseTool, "_InjectedArgs"]] = {}
+
+
 def _get_all_injected_args(tool: BaseTool) -> _InjectedArgs:
     """Extract all injected arguments from tool in a single pass.
 
+    Results are cached by tool identity so the expensive type-hint and schema
+    inspection only runs once per unique tool object across ToolNode instances.
+
     This function analyzes both the tool's input schema and function signature
     to identify all arguments that should be injected (state, store, runtime).
 
@@ -1854,6 +1863,11 @@ def _get_all_injected_args(tool: BaseTool) -> _InjectedArgs:
     Returns:
         _InjectedArgs structure containing all detected injections.
     """
+    tool_id = id(tool)
+    entry = _INJECTED_ARGS_CACHE.get(tool_id)
+    if entry is not None and entry[0] is tool:
+        return entry[1]
+
     # Get annotations from both schema and function signature
     full_schema = tool.get_input_schema()
     schema_annotations = get_all_basemodel_annotations(full_schema)
@@ -1899,10 +1913,12 @@ def _get_all_injected_args(tool: BaseTool) -> _InjectedArgs:
         if _get_injection_from_type(type_, ToolRuntime):
             runtime_arg = name
 
-    return _InjectedArgs(
+    result = _InjectedArgs(
         state=state_args,
         store=store_arg,
         runtime=runtime_arg,
         all_injected_keys=all_injected_keys,
         _optional_state_args=_optional_state_args,
     )
+    _INJECTED_ARGS_CACHE[tool_id] = (tool, result)
+    return result