idea: show the fee below the address on the Sign With Device screen, like Trezor does

[piotr-iohk]

Problem or use case

On the "Sign With Device" screen (on-chain send from a Trezor), the phone shows the amount and the destination address, but not the fee. The Trezor shows amount, address and fee, so the user can only verify the fee on the device and has nothing on the phone to compare it against. From the 2.5.0 QA session (sheet 11 Sep 2026, row "On Trezor, do amount and fee match the phone; can I approve?", rated 2).

Proposed solution

Show the network fee below the address, in the same style as the address block (e.g. caption "FEE (CONFIRM ON DEVICE)" + sats and fiat), so amount, address and fee can all be checked against what the Trezor displays. The fee estimate is already known from the Confirm screen (satsPerVByte is passed into HwSendSignScreen); the exact mining fee is available once the device returns the signed transaction (HwSendViewModel, result.miningFeeSats).

Alternatives considered

• Show the total (amount + fee) instead of a separate fee line.
• Keep as is and rely on the device display only.

Additional context

• Code (release-2.5.0): HwSendSignScreen.kt L121-135 renders BalanceHeaderView (amount) and the address (hardware__send_confirm_address); no fee row.
• iOS HwSendSignView.swift (L32-35) also shows only the address — the same idea applies to iOS; a bitkit-ios counterpart can be opened if wanted.
• Design: docs/screens-map.md maps HwSendSignScreen.kt → "Send (Hardware Device) (On-chain) › Sign with Hardware Device".
• Related: idea: Show address on Transfer from Trezor #1087 (idea: show address on Transfer from Trezor), Trezor send UI polish #1203 (Trezor send UI polish), epic: Trezor Hardware Wallet UI #998 (Trezor HW epic).
• Environment: Android 2.5.0 (189), regtest screenshot; same on mainnet.