Re-add the 127.0.0.1 callbacks to the dev host allowlist (now registered in the
Google console alongside the localhost ones). Deriving the redirect_uri from the
request host keeps the whole round-trip — login, Google callback, and the
session/state cookie — on one origin; a cross-host fallback (127.0.0.1 → the
fixed localhost callback) would silently lose the OAuth state, since a session
cookie set on 127.0.0.1 is never sent to localhost. Clarify that in the comment
and cover all four hosts in the unit test.
peter
1af679bfc5