Python: Fix MCP tool calls sending empty arguments when inputSchema lacks properties

[giles17]

Fixes a bug where MCPStreamableHTTPTool (and other MCP tool types) sends empty {} arguments to the MCP server when the server's inputSchema has no properties key (e.g., {"type": "object"}).

Motivation and Context

Description

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

[markwallace-microsoft]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
packages/core/agent_framework
_tools.py	724	82	88%	176–177, 300, 302, 319–321, 328, 346, 360, 372, 377, 379, 386, 419, 490–492, 533, 555–583, 618, 626, 869, 1121, 1178, 1182, 1261–1265, 1283, 1285–1286, 1398, 1402, 1452, 1454, 1470, 1472, 1536, 1563, 1620, 1688, 1867–1868, 1895, 1903, 1916, 1926–1927, 1962, 2018, 2050
TOTAL	16809	2110	87%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
4013	225 💤	0 ❌	0 🔥	1m 11s ⏱️

[Copilot]

Pull request overview

Fixes MCP tool invocation dropping tool-call arguments when an MCP server returns an inputSchema without properties (e.g., {"type":"object"}), by ensuring the dynamically generated Pydantic input model preserves extra fields.

Changes:

• Update JSON-schema → Pydantic model generation to allow extra fields when properties is missing/empty.
• Add a regression test intended to ensure MCPStreamableHTTPTool forwards arguments for schemas without properties.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
python/packages/core/agent_framework/_tools.py	Generates Pydantic models with extra="allow" for schemas missing/empty properties, preventing argument loss during model_validate/model_dump.
python/packages/core/tests/core/test_mcp.py	Adds a regression test covering MCP tool schemas without properties / with empty properties.