UTXO selection: more emphatically recommend avoiding HD keys used by other wallets/networks

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From BCR:

I think it would be a good idea to have a strong recommendation that wallets should not use an UTXO from block 661647 (BCH/XEC split) or earlier since there is no way for the wallet to know if those outputs have been spent or not on another chain.

And resolution:

Ya, unfortunately, even that wouldn’t be enough. A lot of users have hierarchical-deterministic wallets from before the BCH/BTC split (and BSV and XEC), so wallets which could possibly have been imported (or are otherwise simply shared) are vulnerable, even if the UTXOs are new (if the user continued making transactions on the other chains).

I think that scenario is technically covered by Wallet UTXO Selection criteria 2, but maybe it would be valuable to add a more explicit caveat (with some bolding) at the end of the section… I’ll try to do that too, thanks!