`tests/mail-store.test.ts` exercises the `entries` derived rune
with handcrafted inbox + sent fixtures:
- personal messages exchanged with one race collapse into a
per-race thread with messages sorted oldest → newest;
- system mail (`sender_kind=system`) and admin notifications
(`sender_kind=admin`) surface as stand-alone items even when a
race-name snapshot is present;
- the caller's own paid-tier broadcasts (`broadcast_scope=
game_broadcast`) render as stand-alone outgoing items;
- `unreadCount` counts inbox rows with `readAt === null`.
The store fields are mutated directly to avoid wiring a fake
`GalaxyClient`; the underlying `$derived` rune fires whenever
those fields change.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>