StoredEvent gains sessionSequence: Long (per-session monotonic); existing
sequence field becomes the global monotonic cursor across the entire store.
SqliteEventStore allocates both counters inside the same BEGIN IMMEDIATE
transaction and emits to a global MutableSharedFlow after commit.
InMemoryEventStore mirrors this with an AtomicLong global counter and a
suspend-on-overflow SharedFlow. EventStore interface gains subscribeAll()
and lastGlobalSequence(). Contract tests updated and extended to cover
global-sequence and cross-session subscribeAll invariants.
kami
70420083ac