Release v15.34.7

Fixed

• Event properties typed as a [DerivedType] base (abstract/interface with derived types) now round-trip with their discriminator and concrete subtype properties intact. Previously the type discriminator and all subtype-specific properties were stripped on append, causing read-side deserialization to fail with "Cannot create an instance of <abstract type>".

Summary

Two complementary fixes restore polymorphic serialization for event content:

• The JSON schema generator now emits an open object schema for base types that have registered derivatives, so the schema-driven storage conversion preserves the full payload instead of stripping it to the base type's properties.
• The client event serializer now ensures the derived-type converter is present in its options, so the discriminator and concrete properties are actually written into the event content.