653c6c050b
Protocol: - history.rs: derive_history_key (HKDF from seed, info="warzone-history") - encrypt_history / decrypt_history (ChaCha20-Poly1305, WZH1 magic) - 2 new tests (roundtrip + wrong seed), total 19/19 CLI: - `warzone backup [output.wzb]` — exports all sessions + pre-keys as encrypted blob (only your seed can decrypt) - `warzone restore <input.wzb>` — imports backup, merges (no overwrite) - Backup format: WZH1 magic + nonce + encrypted JSON Storage: - export_all() — dumps sessions + pre-keys as base64 JSON - import_all() — merges backup data (skip existing entries) Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>