Copilot for Xcode stuck on “Sign In” even after successful browser authorization

description
I am unable to sign in to GitHub Copilot for Xcode on my M4 Pro Mac running macOS Sequoia 15.5..

After clicking “Sign In” in the Copilot for Xcode app:
• A browser window (Safari) opens
• GitHub successfully authorizes the device
• I receive the message: “You’re all set!”
• However, the Copilot app still shows “Sign In” and never updates to a logged-in state

This does not happen on my other Mac (also running Sequoia), where everything works fine.

Steps to Reproduce

Open GitHub Copilot for Xcode
Click “Sign In”
Authenticate via browser
See “You’re all set” in the browser
Copilot app does not update — still shows “Sign In”
Expected Behavior

Copilot app should update to show I’m signed in, allowing integration with Xcode

Environment
• macOS: Sequoia 15.5 (24F74)
• Mac: M4 Pro MacBook Pro
• Copilot for Xcode: latest version from GitHub
• Browser: Safari (also tried Chrome)
• GitHub account: Copilot subscription active
• Also tried:
• Deleting keychain entries
• Full reinstall of app