Notification components

Shared notification components provide:

semantic info/success/warning/error banners;
normal-flow banner rails;
host-configurable horizontal and top insets so owning screens can align banners with their existing content padding without double spacing;
session notification metadata/event merging;
inline-renderer injection;
banner and modal routing callbacks;
optional owner-provided asynchronous dismissal;
immediate local suppression only after successful owner dismissal;
opt-in optimistic suppression that remains hidden after synchronization failure;
externally supplied revision keys for a persistent host dismissal cache;
local fallback for hosts that have not adopted server dismissal;
terminal-snapshot protection against stale event resurrection;
fresh-host TTL filtering with mounted-host stickiness;
accessibility labels and action semantics.

Maintainer entry points:

src/notifications/NotificationBanner.tsx
src/notifications/NotificationBannerHost.tsx
src/notifications/SessionNotificationsHost.tsx

Components do not choose application/session ownership or platform modal fallback. Mobile supplies optimistic revision-scoped cache policy. Desktop supplies server-authoritative success-only policy and leaves a notification visible when owner dismissal fails.

Mobile notification hosts use the same native transparent modal boundary as ordinary action-response modals, so the backdrop covers the whole application window. Desktop renders modal notifications through its documented inline fallback.