feat: add Trezor hardware wallet support

[chasebrownn]

Trezor hardware wallet support

Motivation

The library previously only supported Ledger for signing. Teams using Trezor had no path to propose transactions through safe-utils.

What's added

Safe.sol — Trezor signing path in sign()

The sign() function now reads a HARDWARE_WALLET environment variable (defaults to ledger) and branches accordingly:

HARDWARE_WALLET=trezor forge script ... --ffi

When trezor is selected, sign() calls cast wallet sign --trezor <safeTxHash> via vm.ffi instead of using Ledger's EIP-712 --data path. One post-processing step is required: Trezor signs via eth_sign, which prepends \x19Ethereum Signed Message:\n32 to the hash. Safe's checkNSignatures detects this signature type by checking v >= 31, so the recovery byte is incremented by 4 (output[64] += 4) before returning.

README.md

• Clarified that the derivation path argument applies to both Ledger and Trezor.
• Added the HARDWARE_WALLET=trezor env var usage example.
• Updated the sign() note to cover both --ledger and --trezor flags.

Why not --trezor directly?

cast wallet sign --trezor --data <EIP-712 json> is not supported by Trezor's firmware — it only handles raw message signing (eth_sign), not structured data (eth_signTypedData). Passing the raw safeTxHash and adjusting v is the correct workaround.

[aviggiano]

Hi there,

Thanks for your submission. I will review this until the end of the week and we'll get this merge soon

[aviggiano]

Hey

This looks go to be merged

I don't have a Trezor so haven't tested it, and the unit testing support for this library is very inconvenient. So we should expect users to do their own testing