Worked on the LedgerHQ/device-sdk-ts repository to deliver targeted improvements for off-chain message signing workflows. Focused on adding Domain Header support, enabling applications to specify domains within signing requests for better structuring and context. Enhanced APDU error reporting by introducing clearer, structured error messages, which improved diagnostics and reliability for developers integrating with signer-solana. All changes were implemented in TypeScript, emphasizing robust API development and comprehensive error handling while maintaining backward compatibility. The work addressed specific issues with app_domain handling and APDU responses, resulting in a more reliable and developer-friendly experience for full stack teams working with off-chain signing.