refactored mutator to listen for returned data from event listeners

app/src/core/events/Event.ts

@@ -1,3 +1,8 @@
+export type EventClass = {
+   new (params: any): Event<any, any>;
+   slug: string;
+};
+
 export abstract class Event<Params = any, Returning = void> {
    _returning!: Returning;
 
@@ -9,7 +14,9 @@ export abstract class Event<Params = any, Returning = void> {
    params: Params;
    returned: boolean = false;
 
-   validate(value: Returning): Event<Params, Returning> | void {}
+   validate(value: Returning): Event<Params, Returning> | void {
+      throw new EventReturnedWithoutValidation(this as any, value);
+   }
 
    protected clone<This extends Event<Params, Returning> = Event<Params, Returning>>(
       this: This,
@@ -39,3 +46,13 @@ export class InvalidEventReturn extends Error {
       super(`Expected "${expected}", got "${given}"`);
    }
 }
+
+export class EventReturnedWithoutValidation extends Error {
+   constructor(
+      event: EventClass,
+      public data: any
+   ) {
+      // @ts-expect-error slug is static
+      super(`Event "${event.constructor.slug}" returned without validation`);
+   }
+}