so in the meantime is it safe to do any transaction at all ? what if i happen to receive/send money with a counterparty using an old version of the wallet ?
[sorry for the naive question, it's my first "fork" experience

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If an old wallet sends to you, you won't see the transaction coming in. If you send to somebody with an old wallet, neither will they.
The only difference is that your wallet is the correct one. As soon as the old user updates his wallet, he will see the coins coming in.
Unless of course the old fork stays in existence by people not updating, but with the difficulty on that fork it seems extremely unlikely as it will take forever for a block to be found and people will notice their transactions aren't working ;-)