WebChat streaming support via teamapptester

[tracyboehrer]

When using teamsapptester --channel-id webchat, streaming response fail with a 405:

System.Net.Http.HttpClient.Microsoft.Agents.Builder.RestChannelServiceClientFactory.ClientHandler: Information: Sending HTTP request POST http://localhost:58065/_connector/v3/conversations/b704f5d8-7e97-4daa-8937-285b4fb7c365/activities/41858ea4-cbf8-48ca-aa63-d79956820e00
System.Net.Http.HttpClient.Microsoft.Agents.Builder.RestChannelServiceClientFactory.ClientHandler: Information: Received HTTP response headers after 13.2109ms - 405

The same agent using Teams as the channel works as expected.

[m365-agent-toolkit-assistant]

👋 Hi @tracyboehrer,

Thank you for reporting this issue! We want to let you know that:

⏱️ Our team will personally review your issue
🎯 You can expect a response within 2 business days

✨ This is an AI-generated initial response
🤖 AI-Generated Preliminary Analysis:

Your streaming 405 error with teamsapptester --channel-id webchat is a known limitation. Streaming support (partial, real-time responses) is currently not enabled for the WebChat channel in Microsoft 365 Agents Toolkit test environments (teamapptester).

• Confirmed Scope: Streaming works on the Teams channel, but not with WebChat (GitHub Issue #2251, Teams docs 12069).
• Technical Reason: Teams supports streaming with both markdown and (limited) partial Adaptive Cards in the Teams channel only, not over REST APIs or test WebChat channels.
• Workaround: Test streaming via the actual Teams client (desktop/web). For WebChat, only full responses are supported.

Action: Use Teams as your channel for streaming scenarios until Microsoft enables this for WebChat. Track issue #2251 for updates.

✨We'd love your feedback! Please take a moment to fill out our survey.

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Note: This is an automated first response generated by AI. A human team member will review your issue and provide a more detailed response soon. We appreciate your patience!

[tracyboehrer]

Missed some details: Using Agents SDK. I'm on the Agents SDK team. Ping me, or Sarah Critchley, directly if needed.