Mode D: import an existing mnemonic

Standard BIP-39 import with checksum validation. Use this to recover a wallet or to bring a seed generated elsewhere onto the device.

The checksum is validated before anything is stored, and the resulting fingerprint is displayed prominently so you can confirm you typed it correctly. A single wrong word usually fails the checksum. A wrong word that still checksums produces a completely different wallet, so check the fingerprint.

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