fix(autogen-ext): skip LangChain callback-manager (run_manager) when inferring tool args schema

[godququ5-code]

Summary

Fixes #6385.

LangChainToolAdapter inferred a pydantic args model from the callable's signature when a tool provided no args_schema. LangChain injects a run_manager (CallbackManagerForToolRun / its async variant) into a tool's _run/_arun, and pydantic cannot generate a schema for that type, so constructing the adapter raised Unable to generate pydantic-core schema for ...CallbackManagerForToolRun (e.g. GoogleDriveSearchTool).

• In _langchain_adapter.py, when inferring fields, skip parameters whose annotation resolves to a LangChain callback-manager type. Detection unwraps Optional[...]/Union[...] and also falls back to the conventional run_manager parameter name for unresolvable (string) annotations (the module uses from __future__ import annotations).
• The adapter never passed a callback manager to the underlying tool, so omitting run_manager from the schema is correct — the tool still runs without it (it defaults to None).
• Adds a regression test (test_langchain_tool_adapter_skips_run_manager) using a tool without an explicit args_schema.

Test plan

• pytest python/packages/autogen-ext/tests/tools/test_langchain_tools.py — passes (2 tests).

[gnanirahulnutakki]

Thanks for fixing this adapter failure. I reproduced the original path and found two follow-ups before the change is complete: LangChain also reserves callbacks, which still triggers the same schema-generation crash, and the new test needs presence guards for optional schema keys to pass Pyright. I included minimal fixes and focused validation results inline.

[gnanirahulnutakki]

Could we filter callbacks by name here as well? The pinned langchain-core defines FILTERED_ARGS = ("run_manager", "callbacks"), and Callbacks is a sequence of callback handlers, so _is_callback_manager_annotation does not match it. I reproduced this with a no-schema tool whose _run accepts callbacks: Callbacks = None: constructing LangChainToolAdapter raises PydanticSchemaGenerationError for BaseCallbackHandler. Using k in ("run_manager", "callbacks") and extending this regression test to include callbacks fixes the crash; focused pytest, Pyright, mypy, and Ruff all pass.

[gnanirahulnutakki]

Pyright reports three reportTypedDictNotRequiredAccess errors here because parameters, properties, and required are optional TypedDict keys. The earlier test in this file already uses the safe pattern: assert each key is present before indexing it. Adding assert "parameters" in schema, assert "properties" in schema["parameters"], and assert "required" in schema["parameters"] makes targeted Pyright pass with 0 errors.

[gnanirahulnutakki]

Re-reviewed exact head c1b1fc24cfb4. Both findings are resolved: callbacks is filtered alongside run_manager, and the tests now guard optional TypedDict keys before indexing. The three focused tests, targeted Pyright, targeted mypy, and Ruff all pass locally.

[ErenAta16]

Verified the detection logic against the cases it needs to cover, replicating the helper standalone:

bare CallbackManagerForToolRun          -> detected
Optional[CallbackManagerForToolRun]     -> detected
Union[AsyncCallbackManagerForToolRun, None] -> detected
int                                     -> not detected  (control)
Optional[int]                           -> not detected  (control)
inspect.Parameter.empty                 -> not detected

The Union unwrapping matters because Optional[CallbackManagerForToolRun] is how LangChain's own tool templates declare it, so handling only the bare type would have missed the common case. Covering types.UnionType alongside typing.Union also picks up X | None syntax, which is what a tool written on 3.10+ will use.

The name-based fallback is doing real work rather than being defensive padding, and it's worth spelling out why in case someone later reads it as redundant. This module has from __future__ import annotations, so annotations arrive as strings, and a string annotation can't be resolved by issubclass:

is_cb("Optional[CallbackManagerForToolRun]") -> False

That's precisely the situation the run_manager name check catches. Without it the type check would silently do nothing in exactly the module the fix targets, which would be a nasty way to have a "working" fix that isn't. Worth a brief comment saying the fallback exists because of the postponed-annotations import, since that link isn't obvious from the code alone.

Wrapping the langchain_core.callbacks.manager import in try/except ImportError is also right: this adapter is an optional extra, so the helper shouldn't hard-require the symbols to exist at import time.

Two small things:

The test tool declares run_manager on both _run and _arun. Worth confirming the fix path is exercised for the sync and async signatures separately, since _arun takes AsyncCallbackManagerForToolRun and a fix that only unwrapped the sync type would still pass a test that only checks the adapter constructs.

Since the reported failure is a hard exception at adapter-construction time (Unable to generate pydantic-core schema for ...CallbackManagerForToolRun), it'd be worth asserting the inferred schema doesn't contain run_manager in addition to asserting construction succeeds. Constructing successfully proves the crash is gone; asserting the field is absent proves it was excluded rather than coerced into something the model would then be asked to supply.

[gnanirahulnutakki]

The repository-pinned formatter still fails on exact head 315e4f04: uv run --frozen ruff format --check packages/autogen-ext/tests/tools/test_langchain_tools.py reports this file would be reformatted and collapses both new _run/_arun signatures onto one line. Please run the pinned formatter before CI. The 4 focused tests, targeted Pyright and mypy, and Ruff lint otherwise pass locally.

[godququ5-code]

Fixed the pinned Ruff formatting issue in test_langchain_tools.py. The callback-manager filtering logic and sync/async regression coverage are unchanged. Targeted tests and type checks pass locally.

[gnanirahulnutakki]

Re-verified exact head 7b5e64de. The incremental delta only applies the repository-pinned formatting: ruff format --check and Ruff lint now pass, all 4 focused adapter tests pass, Pyright reports 0 errors, and mypy reports no issues in the adapter and its test. The callback-manager filtering logic and sync/async regression coverage are unchanged from the previously verified head, so the formatter finding is resolved.

[ErenAta16]

Formatting fix noted, and good that the detection logic and the sync/async coverage stayed untouched in that pass. My earlier review points still stand as written; nothing in a Ruff-only commit changes them.