The agent signs in on its own whenever acp_token.json holds a valid
token, so Sign in and Change account never reached Google and could not
switch accounts. Browser sign-in now moves the saved token aside for the
sign-in's scope. Success keeps the new token; failure, cancel, or timeout
puts the old one back unless the agent already saved a new one. Driver
start restores a token left aside by a sign-in that never finished.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>