Session State Management

Long-running conversations require careful state management. Per session:

Persist to local DB (SQLCipher in Signal). Encrypted at rest with device passphrase.

Concurrency: multiple devices, multiple conversations, can be tricky. Signal uses per-session locks.

Recovery scenarios:

• App crash mid-encrypt: state may be advanced; if not yet sent, peer never sees the message and will fall behind. Mitigation: only commit state AFTER successful network send.
• Lost device: new device has no state. Either ask peer to "reset session" or use Signal's "linked device" mechanism that shares some state via QR.
• Key compromise: hard to recover. Signal's "safety number changed" warning prompts users to re-verify out-of-band.

Multi-device:

• Each device has its own identity key.
• Messages encrypted N times (once per recipient device).
• Sender keys (server-side) help reduce O(N) encryption cost in groups.

State explosion: a daily-chat user with 5 devices, 50 contacts: 250 active sessions. Each session has root/chain/cached mks.