Just had an insight: Ecash wallets with the same seed phrase can be synced across different devices! This would eliminate one of the last big issues I see with ecash wallets because they can only be used locally (in one wallet only, i.e. different wallets of the same user will have a different balance) –– BUT NOT ANYMORE!

If two wallets use the same seed phrase, they generate the same ecash. The difference between two wallets is the counter with which the secret derivation is iterated by. That means if a user uses wallet_1 to reach counter_1 and then uses the same seed in wallet_2, then counter_2 can iterated until no ecash can be restored "from backup" anymore. Now, both wallets have the same state again (same ecash, same balance, etc...).

So instead of using the `/v1/restore` API only for backup restore, it can also be used to sync multiple wallet instances of the same seed phrase to each other! DAMN!