Max fills in a token's balance, cut down to the 18 decimal places the confirmation screen accepts, or for ETH the exact balance minus the fee reserve the confirmation screen's balance check gates on. An ETH fee estimate that finishes after the Send screen was left, or its address, holding, recipient or amount changed, fills nothing in. The confirmation screen works a max ETH amount out again from its own fee estimate and signs it with that estimate's fee fields, so a fee that rose before signing cannot push amount plus fee above the balance. validateTransfer() still gates every send, the check that ETH covers a token send's fee included. Where there is nothing to fill in, a flash message says why. Model: opus-5-5