.NET: declare Magentic protocol messages

[he-yufeng]

Summary

• declare the single ChatMessage and ResetChatSignal messages that MagenticOrchestrator sends at runtime
• add a protocol regression test so the workflow descriptor keeps those outgoing message types

Fixes #5774.

To verify

• dotnet build .\src\Microsoft.Agents.AI.Workflows\Microsoft.Agents.AI.Workflows.csproj -f net10.0 --no-restore --tl:off
• dotnet test --project .\tests\Microsoft.Agents.AI.Workflows.UnitTests\Microsoft.Agents.AI.Workflows.UnitTests.csproj -f net10.0 --filter-class Microsoft.Agents.AI.Workflows.UnitTests.MagenticOrchestratorTests
• dotnet test --project .\tests\Microsoft.Agents.AI.Workflows.UnitTests\Microsoft.Agents.AI.Workflows.UnitTests.csproj -f net10.0 --filter-class Microsoft.Agents.AI.Workflows.UnitTests.MagenticManagerTests
• dotnet format .\src\Microsoft.Agents.AI.Workflows\Microsoft.Agents.AI.Workflows.csproj --verify-no-changes --no-restore
• dotnet format .\tests\Microsoft.Agents.AI.Workflows.UnitTests\Microsoft.Agents.AI.Workflows.UnitTests.csproj --verify-no-changes --no-restore
• git diff --check

[Copilot]

Pull request overview

This PR fixes Magentic orchestration protocol metadata in the .NET workflows layer by explicitly declaring the runtime outbound message types that MagenticOrchestrator sends, preventing protocol validation failures when converting workflows to AIAgent. It also adds a regression unit test to ensure these sent message types remain declared in the protocol descriptor.

Changes:

• Declare ChatMessage and ResetChatSignal as outbound (Sends) message types in MagenticOrchestrator’s protocol configuration.
• Add a unit test validating MagenticOrchestrator.DescribeProtocol() includes the expected Sends types (including the newly declared ones).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
dotnet/src/Microsoft.Agents.AI.Workflows/Specialized/Magentic/MagenticOrchestrator.cs	Extends protocol declaration to include ChatMessage and ResetChatSignal as allowed outgoing message types.
dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/MagenticOrchestratorTests.cs	Adds a regression test asserting the orchestrator’s protocol declares the relevant Sends message types.

[lokitoth]

Good catch and fix, @he-yufeng