GitHub Copilot CLI 1.0.9 on Windows appears to have a regression with third-party remote MCP servers in prompt mode (`-p`) and new non-interactive sessions.

[SkyIsWhite]

Describe the bug

GitHub Copilot CLI 1.0.9 on Windows appears to have a regression with third-party remote MCP servers in prompt mode (-p) and new non-interactive sessions.

What I expected:
A configured remote MCP server should be available in copilot -p, same as in interactive mode, per the Copilot CLI docs.

What actually happens:

• web_search works in copilot -p, so networking is available.
• mixpanel is configured in ~/.copilot/mcp-config.json.
• In interactive mode, Mixpanel can authenticate and connect successfully.
• But in copilot -p and fresh copilot -i sessions, Mixpanel repeatedly fails with:
  invalid_token / Authentication required
• The model then says Mixpanel MCP is not available in the session.
• In some runs, there are also EPIPE: broken pipe, write errors.

Why this looks like a CLI regression:

• The same workflow reportedly worked on CLI 1.0.7.
• I cannot find any docs saying -p should exclude MCP tools.
• Official docs describe MCP servers as available after configuration, and -p as programmatic prompt execution.

Environment:

• OS: Windows
• Copilot CLI: 1.0.9
• MCP server: remote HTTP MCP (https://mcp.mixpanel.com/mcp)
• Third-party MCP affected: Mixpanel
• Built-in/other networked tools still work: web_search, microsoft-learn, github-mcp-server

Relevant symptoms from logs:

• Server mixpanel requires authentication, initiating OAuth flow
• Failed to start MCP client for remote server mixpanel: ... {"error":"invalid_token","error_description":"Authentication required"}
• In other sessions: Successfully authenticated with mixpanel and Started MCP client for remote server mixpanel with OAuth
• Yet copilot -p still says Mixpanel MCP is unavailable
• Some -p runs also show EPIPE: broken pipe, write

This suggests a bug in MCP OAuth reuse/session handling or tool exposure for third-party remote MCP servers in non-interactive mode.

Affected version

No response

Steps to reproduce the behavior

No response

Expected behavior

No response

Additional context

No response

[Lyve1981]

Interactive mode is broken also, see #2176