[cesarb]

> I lost all my history when moving phones, as I chose not to back up my messages (who would?).

The trick is to use the local backup option (it's encrypted with a key from the whatsapp servers, but all the files are kept on your device), and use syncthing to copy the whole folder structure (containing the backup and the media) to the new phone before installing whatsapp. When first run, the whatsapp client detects the presence of that backup, asks whether you want to use it, gets the key from the whatsapp servers (after you authenticate your account), and restores the backup.

(By the way, Signal can do the same trick, but it's slightly less user-friendly: the encryption key does not come from the signal servers, it's a sequence of numbers you have to write down and type on the new phone.)