From bbb105dfe1d7caf37bcb09e235b3f8de460c07d7 Mon Sep 17 00:00:00 2001
From: Chester Curme <chester.curme@gmail.com>
Date: Tue, 11 Aug 2026 11:56:32 -0400
Subject: [PATCH] use _get_type_hints

---
 libs/core/langchain_core/tools/structured.py | 14 ++++-
 libs/core/tests/unit_tests/test_tools.py     | 59 ++++++++++++++++++++
 2 files changed, 71 insertions(+), 2 deletions(-)

diff --git a/libs/core/langchain_core/tools/structured.py b/libs/core/langchain_core/tools/structured.py
index e9643a0ad8..cba45463d4 100644
--- a/libs/core/langchain_core/tools/structured.py
+++ b/libs/core/langchain_core/tools/structured.py
@@ -28,6 +28,7 @@ from langchain_core.tools.base import (
     ArgsSchema,
     BaseTool,
     _get_runnable_config_param,
+    _get_type_hints,
     _is_injected_arg_type,
     create_schema_from_function,
 )
@@ -256,10 +257,19 @@ class StructuredTool(BaseTool):
         fn = self.func or self.coroutine
         if fn is None:
             return _EMPTY_SET
+        # Resolve annotations via `_get_type_hints` (rather than reading raw
+        # `signature` annotations) so postponed annotations -- e.g. from
+        # `from __future__ import annotations` or quoted forward references --
+        # are recognized. `include_extras=True` preserves `Annotated` metadata
+        # so `InjectedToolArg` markers survive resolution. Fall back to the raw
+        # per-parameter annotation when a hint can't be resolved. Mirrors
+        # `BaseTool._injected_args_keys` in `base.py`.
+        params = signature(fn).parameters
+        hints = _get_type_hints(fn, include_extras=True) or {}
         return frozenset(
             k
-            for k, v in signature(fn).parameters.items()
-            if _is_injected_arg_type(v.annotation)
+            for k, v in params.items()
+            if _is_injected_arg_type(hints.get(k, v.annotation))
         )
 
 
diff --git a/libs/core/tests/unit_tests/test_tools.py b/libs/core/tests/unit_tests/test_tools.py
index f23fd9052a..1751627d9e 100644
--- a/libs/core/tests/unit_tests/test_tools.py
+++ b/libs/core/tests/unit_tests/test_tools.py
@@ -3781,6 +3781,65 @@ def test_base_tool_subclass_injects_postponed_annotated_arg() -> None:
     assert captured["injected"] == "value"
 
 
+def test_structured_tool_injects_postponed_annotation_runtime() -> None:
+    """`StructuredTool` must resolve postponed / forward-ref injected args too.
+
+    `StructuredTool._injected_args_keys` inspects the wrapped `func`/`coroutine`
+    instead of `_run`, so it needs the same hint resolution as
+    `BaseTool._injected_args_keys`. A quoted forward reference exposes a raw
+    string annotation at `signature()` time; without resolution the injected
+    arg is omitted from `_injected_args_keys` and the call raises `TypeError`.
+    Fixes #39568.
+    """
+
+    class MultiplyInput(BaseModel):
+        a: int
+        b: int
+
+    captured: dict[str, Any] = {}
+
+    # Quoted forward reference -> raw string annotation "_CustomRuntime".
+    @tool(args_schema=MultiplyInput)
+    def multiply(a: int, b: int, runtime: "_CustomRuntime") -> int:
+        """Multiply two numbers."""
+        captured["runtime"] = runtime
+        return a * b
+
+    assert "runtime" in multiply._injected_args_keys
+
+    runtime = _CustomRuntime(data={"scale": 10})
+    result = multiply.invoke({"a": 2, "b": 3, "runtime": runtime})
+    assert result == 6
+    assert captured["runtime"] is runtime
+
+
+def test_structured_tool_injects_postponed_annotated_arg() -> None:
+    """`StructuredTool` must resolve postponed `Annotated[..., InjectedToolArg]`.
+
+    `include_extras=True` when resolving hints preserves the `InjectedToolArg`
+    metadata, so annotated injected args on the wrapped function are still
+    detected. Fixes #39568.
+    """
+
+    class QueryInput(BaseModel):
+        query: str
+
+    captured: dict[str, Any] = {}
+
+    # Quoted forward reference to a postponed `Annotated` injected arg.
+    @tool(args_schema=QueryInput)
+    def echo(query: str, injected: "Annotated[str, InjectedToolArg]") -> str:
+        """Echo the query."""
+        captured["injected"] = injected
+        return query
+
+    assert "injected" in echo._injected_args_keys
+
+    result = echo.invoke({"query": "hi", "injected": "value"})
+    assert result == "hi"
+    assert captured["injected"] == "value"
+
+
 class CallbackHandlerWithToolCallIdCapture(FakeCallbackHandler):
     """Callback handler that captures `tool_call_id` passed to `on_tool_start`.