Release v15.38.0

Added

• ReadModelScenario<T>.Instances and InstanceForEventSourceId(id) for asserting a specific materialized read model when a projection spans multiple event sources — for example a [Join] whose join-source event is seeded before the entity under test, which previously shadowed it in Instance.

Fixed

• Read-model properties that are collections of bare concepts (for example IReadOnlyList<ConceptAs<string>>) no longer persist empty to MongoDB — the concept elements are now stored as their underlying values, matching the in-memory sink.