async def _process_header_at_tip(self) -> bool:
        """Returns:
        False - boring fast-forward: we already have this header as part of this blockchain from another interface,
        True - new header we didn't have, or reorg
        """
        height, header = self.tip, self.tip_header
        async with self.network.bhi_lock:
            if self.blockchain.height() >= height and self.blockchain.check_header(header):
                # another interface amended the blockchain
                return False
            await self.sync_until(height)
            return True
Returns:
        False - boring fast-forward: we already have this header as part of this blockchain from another interface,
        True - new header we didn't have, or reorg
        
electrum/interface.py