fix: allow standalone .invoke() on tools with ToolRuntime parameter

[Ethan T. (gambletan)]

Summary

Fixes #7222

When a @tool-decorated function has a runtime: ToolRuntime parameter, calling .invoke({}) standalone (outside of a LangGraph graph) fails with a Pydantic ValidationError because runtime is treated as a required input field.

Root cause: langchain-core's _parse_input validates tool input against the full args_schema (which includes ToolRuntime as a required field) and does not provide defaults for injected arguments when they are absent.

Fix (two parts):

1. ToolRuntime.__get_pydantic_core_schema__ — makes Pydantic treat ToolRuntime as optional with a None default during schema validation. Handles the bare ToolRuntime type annotation.

2. Patch BaseTool._parse_input — at tool_node.py import time, wraps the original method to handle injected arguments (ToolRuntime, InjectedState, InjectedStore) gracefully:

   • When all injected args are present in the input (ToolNode injection path), delegates to the original implementation unchanged.
   • When injected args are missing (standalone invocation path), validates using tool_call_schema (which already excludes injected fields) and re-adds injected keys with None defaults.

Before:

@tool
def my_tool(runtime: ToolRuntime):
    """Test tool"""
    pass

my_tool.invoke({})  # ValidationError: 'runtime' field required

After:

@tool
def my_tool(x: int, runtime: ToolRuntime) -> str:
    """Test tool"""
    if runtime is not None:
        return f"graph mode: {runtime.tool_call_id}"
    return f"standalone: x={x}"

my_tool.invoke({"x": 42})  # "standalone: x=42"

Test plan

• Standalone .invoke({}) with ToolRuntime parameter succeeds (returns runtime=None)
• Standalone .invoke() with ToolRuntime + other args works
• ToolRuntime[MyContext] (generic) standalone invocation works
• Normal tools (no injected args) are unaffected
• ToolNode injection path still works (all injected args present)
• Async .ainvoke() works
• tool_call_schema still correctly excludes runtime
• All 43 existing test_tool_node.py tests pass
• All 16 test_tool_node_validation_error_filtering.py tests pass

🤖 Generated with Claude Code

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