Built-in task tool fails with "CAPIError: 404 ...." in BYOK/Azure AI Foundry deployments #907
Description
When using the Copilot SDK with a BYOK (Bring Your Own Key) Azure AI Foundry provider, the built-in task tool always fails with error:
CAPIError: 404 The API deployment for this resource does not exist. If you created the deployment within the last 5 minutes, please wait a moment and try again.
The parent session authenticates via Azure AI Foundry and works correctly, but it looks as if subagents are getting spawned with a different model or something.
Environment:
Copilot SDK Version: 2.0.0 (.NET)
.NET Version: 10.0
OS: Linux (Ubuntu 24.04, containerized)
Provider: Azure AI Foundry BYOK (type: "azure")
Model: gpt-5.4
The setup is exactly the same as in #559