Write the handoff for a half-done auth refactor

You have spent 2 days driving an AI agent through a refactor of your JavaScript auth module. It moves session handling from hand-rolled cookies to the team's new SessionStore. You are about halfway, and you go on leave tomorrow. A teammate will carry on, with their own agent session that starts knowing nothing.

Write the handoff note you would leave in the repo for your teammate and their agent.

What you know:

• 6 of 11 routes use SessionStore now (login, refresh, profile, settings, password change, 2FA check), and the old cookie code still serves the other 5 (logout, OAuth callback, account deletion, API token exchange, admin impersonation)
• you tried moving logout early, and it broke signing out across open tabs, so you reverted it
• logged-in users must stay logged in through the deploy, and old cookies must keep working for 30 days
• your chat with the agent runs to 400 messages

Then, in a few sentences: what context lives only in your head and the chat, and why is the chat log a poor handoff?