Messages were in-memory only — gone on leaving the conversation.
- MessageStore: keystore-backed (no plaintext), a capped per-peer JSON list
(last 200). Simple; the encrypted Drift DB is the eventual home at scale.
- MessagesCubit: loads saved history on start (subscribes FIRST, then loads, so
a message arriving during the load isn't dropped) and persists every sent and
received message. Wired via DI + TaneApp(messageStore).
Tests (plain 'test', no hang risk): MessageStore round-trip/per-peer/cap, and a
cubit test that reopens a fresh cubit and sees the saved conversation. Analyzer
clean; run 'flutter test' locally to confirm.