Adds ChatSensitiveVault: a per-wallet random 32-byte key wrapped under a user
passphrase (Argon2id MODERATE KEK + XSalsa20-Poly1305) in an 89-byte local file.
This key encrypts the at-rest rows of "sensitive" conversations INDEPENDENTLY of
the seed-derived chat key, so those rows can't be read by someone who has the
seed but not this passphrase — and a wallet restored from the seed alone can't
read them at all. Losing the passphrase/file makes them unrecoverable by design.
create/unlock/changePassphrase/remove, atomic write + 0600, keyOut zeroed on any
failure. Unit-tested (round-trip, wrong-passphrase zeroing, rekey, no-clobber).
Phase B, step 2 (local vault key).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
DanSandClaude Opus 4.8
84ca1a5cbe