MCP OAuth: 'needs authentication' link never launches any visible auth flow (Atlassian/Jira, macOS, CLI 1.0.83)

Describe the bug

The Atlassian (Rovo) MCP server repeatedly shows a "Jira MCP needs authentication" prompt, but clicking the provided authentication link — or attempting to authenticate manually — never launches any visible auth flow. No browser window/tab opens, no OAuth consent page appears, and nothing surfaces in the UI. The prompt simply reappears, so the server can never be authenticated and its tools are never usable.

This is the browser-launch / auth-hand-off side of MCP OAuth, not the token-bridging bug in #4096 (which is fixed on my version). It looks related to #4400 (browser login URL wrapping/fallback) and #3130 (unable to open browser for auth).

Affected version

GitHub Copilot CLI 1.0.83 (bundled engine used by the Copilot desktop app "agents" window).

Environment

• macOS (Apple Silicon)
• The failing flow is in the app / agents window, which manages its own MCP configuration.
• The standalone terminal CLI has no MCP servers configured (~/.copilot/mcp-config.json = {"mcpServers":{}}, copilot mcp list = "No MCP servers configured", and ~/.copilot/mcp-oauth-config/ does not exist). So the Atlassian server exists only on the app side, and it is the app-side "authenticate" link that dead-ends.

Steps to reproduce the behavior

1. In the Copilot app (agents window), add/enable the Atlassian Remote MCP server (https://mcp.atlassian.com/v1/mcp).
2. When prompted with "Jira MCP needs authentication", click the provided authentication link (or choose to authenticate manually).
3. Observe: no browser opens, no OAuth consent page appears, nothing visible happens.
4. The "needs authentication" prompt returns; the server never becomes authenticated and no atlassian-* tools are exposed.

Expected behavior

Clicking the authentication link should open the system default browser to the OAuth consent URL (or, if the browser cannot be launched, print/copy the raw URL so it can be opened manually) and complete the callback so the server authenticates.

Additional notes

• This consistently blocks my workflow — the Atlassian/Jira MCP tools are never available because auth can never be completed.
• A raw-URL fallback (print the login URL to stdout / provide a copyable link) would at minimum unblock manual authentication when auto-launch fails.

https://mcp.atlassian.com/v1/mcp を有効にした状態で Copilot アプリのエージェントウィンドウのフローを再現し、その後、/.copilot/mcp-config.json、copilot mcp list、/.copilot/mcp-oauth-config/ に記述されたスタンドアロン CLI の状態と比較します。認証リンクの受け渡しとブラウザー起動のエントリポイントを追跡します。完了条件は、リンクによってシステムブラウザーが開くか、コピー可能な raw URL が表示され、コールバック後に Atlassian ツールが利用可能になることです。