Windows CLI becomes unusable when a configured MCP server needs authentication #5234

Describe the bug

starting Copilot CLI in Command Prompt/PowerShell showed “Please use  /login  to sign in to use Copilot” and raw terminal escape codes. The CLI became usable after they authenticated the MCP server through the Copilot desktop app. This suggests an MCP authentication flow may be interfering with CLI startup or sign-in. It was crashing before. A seperate copilot tab had to be used to auth the MCPs before trying again

Affected version

Copilot CLI  1.0.102 

Steps to reproduce the behavior

1. Configure an MCP server that requires authentication.
2. Start Copilot CLI in Windows Terminal using Command Prompt or PowerShell.
3. Observe the crash after ~5 seconds, sign-in message and escape codes.
4. Authenticate the MCP server in the Copilot desktop app, then launch the CLI again; it works.

Expected behavior

The CLI should start and provide a clear way to complete required authentication without becoming unusable or printing terminal escape codes.

Additional context

Windows; screenshot shows Windows Terminal with a Command Prompt profile. The MCP server name and exact auth flow weren’t captured. Related, but not the same: #4957, about MCP startup behavior while GitHub authentication resolves.