Store sync event definitions as Effect Schema and derive Zod only at the bus and OpenAPI edges. Bridge the remaining Zod-native session payloads through Schema annotations so the sync layer no longer needs mixed-schema definition helpers.
Exercise the new SyncEvent and BusEvent Schema overloads end to end and use Schema.isSchema for the conversion check so the mixed-schema path stays explicit and covered.
Overloads BusEvent.define and SyncEvent.define so payload schemas can be passed as Effect Schema values directly. Effect Schemas are converted to Zod via the effect-zod walker since the sync/bus pipelines still use Zod internally. Migrates MessageV2.Event.* to use Schema.Struct directly instead of z.object with .zod references.
Kit Langton