crypter.cpp had zero tests despite guarding every encrypted wallet. Add
8 cases: passphrase round-trip for both KDFs (sha512 method 0 and scrypt
method 1), wrong-passphrase rejection, salt-affects-key, KDF determinism,
bad-parameter rejection (zero rounds / short salt / encrypt-before-key),
the EncryptSecret/DecryptSecret private-key path with a uint256 IV, and
ciphertext-tamper rejection. Round-trip/negative style, no brittle hard-coded
ciphertext. No implementation change (crypter.cpp is correct).
Note captured in the test: the wallet uses a uint256 as the AES IV but
AES-256-CBC consumes only the first 16 (little-endian) memory bytes -- a
subtlety worth remembering for anyone touching the key-encryption path.
Krystie