Keep — somewhere durable, before the address appears
Three places count, and you pick at the moment the key is made: an encrypted file in a folder, the twenty-four words on paper, or sealed behind the fingerprint on this device. Any one of them is enough, and writing the file takes milliseconds. A browser tab is none of them — a key that lives only in a tab dies with it, and the address it made keeps showing a balance nobody can reach. So the rule is narrow: the key is written to a vault file, paper or your fingerprint before the address appears. This page obeys it — mint, keep, then addresses — and it is not in production yet.