fix: ixp extraction tool

[cristian-groza]

Summary

Fixes broken IXP extraction tool invocation caused by LangChain's mishandling of pydantic field aliases.

Problem

After PR #796 switched the extraction tool's args_schema to Attachment, tool calls started failing — kwargs.get("id") and kwargs.get("full_name") came back as None, so attachments.download_async was called with key=None.

Two LangChain bugs are at play:

1. BaseTool._parse_input() extracts each field with getattr(model, alias). When an alias collides with a built-in pydantic model attribute (e.g. schema), this returns the built-in rather than the field value.
2. tool_call_schema rebuilds a subset of the model field-by-field but drops alias and serialization options, so the rebuilt schema no longer matches what the LLM emits.

Attachment aliases every field (id → ID, full_name → FullName, …), so it hits both bugs.

Fix

Introduce ExtractionToolInputSchema — an alias-free mirror of Attachment with the same python field names and annotations — and use it as the tool's args_schema. Sidesteps both LangChain bugs until they're fixed upstream.

Changes

• src/uipath_langchain/agent/tools/extraction_tool.py: define ExtractionToolInputSchema and use it as args_schema; docstring explains the reasoning so future readers don't switch back to Attachment.
• tests/agent/tools/test_extraction_tool.py: replace the args_schema == Attachment assertion with a structural check that the schema's field names and annotations match Attachment.model_fields — guards against drift if
  Attachment evolves.

Test plan

• uv run pytest tests/agent/tools/test_extraction_tool.py passes
• Verify end-to-end: deploy an agent that uses the IXP extraction tool and confirm download_async receives the populated UUID

[andreitava-uip]

nit: these bugs are not what causes it. It was us fixing the bugs via our structured tool subclass that surfaced the issue.