.NET: Remove FunctionCalls and Tool Messages from Handoff passed messages

[Jacob Alber (lokitoth)]

Motivation and Context

The Handoff Orchestration currently does not filter out the HandoffTool FunctionCall messages or the Tool FunctionResult messages. This can cause odd behaviour, such as the LLM ignoring the original user question.

Description

• Add tests checking for removal of FunctionCall and Tool content (fixes.NET: [Bug]: Handoff orchestration does not pass message to the handoff agent #3161, .NET: [Workflows] Handoff tool response appears in chat history, causing inconsistent LLM behavior #3046)
• Add tests checking for propagation of ChatMessages between agents
• Fixes Handoff logic to ensure messages get transferred correctly between agents with appropriate filtering

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.

[Copilot]

Pull request overview

This PR fixes a critical bug in handoff orchestration where FunctionCall and Tool messages from handoff operations were being passed to target agents, causing the LLM to ignore the original user question. The fix filters out these internal workflow mechanics before sending messages to the target agent.

Changes:

• Added regression tests to verify that handoff function calls and tool results are not passed to target agents
• Added regression tests for multi-hop handoff scenarios to ensure proper message propagation
• Implemented FilterHandoffMessages method to remove handoff-related messages before sending to target agents

Reviewed changes

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

File	Description
dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/AgentWorkflowBuilderTests.cs	Added two comprehensive regression tests verifying that handoff targets do not receive handoff function messages in single and multi-hop scenarios
dotnet/src/Microsoft.Agents.AI.Workflows/Specialized/HandoffAgentExecutor.cs	Added FilterHandoffMessages method to filter out handoff function calls and tool results; integrated filtering logic into the handoff message flow