- cancel_signin marks an in-flight attempt and, independently, deletes the
account if that attempt saved it, so a cancel landing after the save but
before the connect's cleanup still removes the token.
- Sign-out runs one at a time (a second call joins it) and refuses new
sign-ins while it runs; it goes round until no window, connect or cancel is
left. The page keeps Sign in with Meta off from pressing Disconnect until
the server has deleted the token.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
