SnapshotTailReader
An optional capability of a store that holds a context's log and its snapshots in one database: reading an aggregate's snapshot and the tail after it in one round trip (me.ahoo.wow.spi.store.Store.snapshotTails). The runtime gives it to the kernel for the aggregate types whose log and primary snapshots are on that one store; the others are read the way every log can: the snapshot, then the tail (readSnapshotTailApart).
The kernel reads through it on a cache miss, and reads apart, warning once and counting the fallback (the observer's me.ahoo.wow.spi.observation.ObservedEvent.StoreFellBack), when it fails.
Functions
ref's snapshot and the tail after it with the request keys before it, as EventLog.readTail reads them from the snapshot's version, as one statement sees them; with no snapshot, every stream of ref and no earlier keys. A failure is thrown.