[dotnet-port] Populate MessageID from TaskStatusUpdateEvent.Status.Message in A2A agent

[qmuntal]

When the Go A2A agent receives a TaskStatusUpdateEvent during streaming, ResponseUpdate.MessageID is now set from Status.Message.ID when the message is present, falling back to the TaskID otherwise.

This aligns with the .NET fix in microsoft/agent-framework#6043.

[Copilot]

Pull request overview

Updates the Go A2A agent’s streaming handling so ResponseUpdate.MessageID is derived from the status update’s embedded message (TaskStatusUpdateEvent.Status.Message.ID) when available, matching the behavior of the referenced .NET fix and improving message correlation during streaming.

Changes:

• Populate ResponseUpdate.MessageID from TaskStatusUpdateEvent.Status.Message.ID when present; otherwise keep the TaskID fallback.
• Add a streaming unit test covering the “status update contains a message” scenario to validate the new MessageID behavior.

Show a summary per file

File	Description
agent/provider/a2aagent/a2a.go	Adjusts streaming status-update mapping to prefer Status.Message.ID for MessageID with TaskID fallback.
agent/provider/a2aagent/a2a_test.go	Adds a test ensuring MessageID is sourced from Status.Message.ID when provided.

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• Files reviewed: 2/2 changed files
• Comments generated: 0

[github-actions]

Cross-Repo Parity Review ✅

This PR is a direct port of the .NET fix from microsoft/agent-framework#6043 and is semantically aligned with the upstream fix.

What was fixed in .NET:
ConvertToAgentResponseUpdate(TaskStatusUpdateEvent) added MessageId = statusUpdateEvent.Status.Message?.MessageId, falling back to TaskId otherwise.

What this PR does in Go:
Sets messageID = e.Status.Message.ID when e.Status.Message != nil, falling back to string(e.TaskID) — an idiomatic Go equivalent of the C# null-conditional operator.

Both implementations are semantically identical. The test coverage mirrors the .NET approach (cases with and without a message in the status update).

No parity issues found.

Generated by Go API Consistency Review Agent for issue #215 · ● 5.3M · ◷