test(core): cover Effect Schema event definitions

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.

packages/opencode/src/bus/bus-event.ts

@@ -23,16 +23,12 @@ export function define<Type extends string, P extends ZodType>(
   properties: P,
 ): { type: Type; properties: P }
 export function define(type: string, properties: unknown) {
-  const zodProperties = isEffectSchema(properties) ? zod(properties) : (properties as ZodType)
+  const zodProperties = Schema.isSchema(properties) ? zod(properties) : (properties as ZodType)
   const result = { type, properties: zodProperties }
   registry.set(type, result as Definition)
   return result
 }
 
-function isEffectSchema(value: unknown): value is Schema.Top {
-  return typeof value === "object" && value !== null && "ast" in value
-}
-
 export function payloads() {
   return registry
     .entries()

packages/opencode/src/sync/index.ts

@@ -117,7 +117,7 @@ export function define<
 }
 
 function toZodObject(value: ZodObject | Schema.Top): z.ZodObject {
-  if (typeof value === "object" && value !== null && "ast" in value) {
+  if (Schema.isSchema(value)) {
     return zod(value as Schema.Top) as unknown as z.ZodObject
   }
   return value as z.ZodObject