The default sender identity (`preferredPrimaryId`) lived only in the
browser-local `identity-storage` Zustand store and was never written to
the server-side synced settings. As a result the choice was lost when
clearing site data or switching browsers, and never appeared in the
exported settings JSON.
Persist the default identity in the synced settings store, keyed per
account (`preferredIdentityIds: Record<accountId, identityId>`), mirroring
the existing per-account `allMailFolderIds`. Per-account keying is required
because JMAP identity ids are account-scoped and would otherwise collide
across accounts / the unified mailbox.
- settings-store: add `preferredIdentityIds` to state, defaults, export
(so it shows in exported JSON), import (with a non-record guard),
rehydrate coercion, and a v6->v7 migration.
- auth-store: add `applyPreferredIdentity()`, invoked in every
`loadFromServer().finally()` (login / OAuth / SSO / switch / restore) so
the synced default reorders the active account's identities once server
settings load (the composer defaults From to identities[0]).
- identity-manager-modal: the star action also writes the choice to the
synced per-account map, triggering server sync + export inclusion.
- identity-store: keep `preferredPrimaryId` in local persist as a sync-off
fallback; synced settings are the durable cross-device source of truth.
- tests: per-account independence, export/import round-trip, non-record
import guard, and v6->v7 migration.
Stefan Hildebrandt
034f7a4b9b