Streamable HTTP error - Session not found

### Describe the bug

I can successfully add and start using MCP. However, after a while, MCP calls start consistently failing with an error.

Streamable HTTP error: Error POSTing to endpoint: {"error":{"code":-32001,"message":"Session not found"},"id":"","jsonrpc":"2.0"}

Exit / resume of Copilot CLI mitigates the issue but is annoying.

### Affected version

GitHub Copilot CLI 0.0.406.

### Steps to reproduce the behavior

_No response_

### Expected behavior

_No response_

### Additional context

- Windows x86_64