If you have one UTXO with 1 BTC in it and you split it into two 0.5BTC UTXOs (ignore fees for now), which one of the two new UTXOs contain the first satoshi from the original UTXO?

From what I understand ordinals/runes just adds some "lens" on top the UTXOs where they get to decide what they think happens to sats as UTXOs are spent and new ones are created.

(Could be wrong, haven't looked too much into the NFT bullshit)