Google OAuth and LAN IPs, repeatedly
Google OAuth rejects LAN-IP redirect URIs at the provider, so testing from a device on the local network always fails and always looks like an integration bug.
Two copies drifted
One idea kept by hand in two places — schema and migration, dev and prod, app and app.
Google rejects LAN-IP redirect URIs outright, so anything driven from a physical device on the local network fails at the provider, not in our code. It needs localhost or a real tunnel. This has bitten more than once — it looks like an OAuth integration bug every time, and it never is.