fix: clone history events to prevent mutation

packages/@eventual/core-runtime/src/deep-clone.ts

@@ -0,0 +1,4 @@
+export function deepClone<T>(item: T): T {
+  // TODO: more efficient deep clone
+  return JSON.parse(JSON.stringify(item));
+}

packages/@eventual/core-runtime/src/providers/executor-provider.ts

@@ -54,7 +54,7 @@ export class RemoteExecutorProvider<Context = undefined>
     executor: WorkflowExecutor<any, any, any>
   ): Promise<{ storedBytes: number }> {
     // provides a shallow copy of the history events.
-    const historyEvents = executor.history.slice(0);
+    const historyEvents = executor.historyCloned.slice(0);
     historyEvents.push(...newHistoryEvents);
     const { bytes } = await this.props.executionHistoryStateStore.updateHistory(
       {

packages/@eventual/core-runtime/src/workflow/workflow-executor.ts

@@ -50,6 +50,7 @@ import {
   type UnresolvedEventualDefinition,
 } from "./eventual-definition.js";
 import { formatExecutionId } from "./execution.js";
+import { deepClone } from "../deep-clone.js";
 
 /**
  * Put the resolve method on the promise, but don't expose it.
@@ -206,13 +207,17 @@ export class WorkflowExecutor<Input, Output, Context = undefined> {
     ) => void;
   } = {};
 
+  // clone the history so it cannot be modified by the user
+  public historyCloned: HistoryStateEvent[];
+
   constructor(
     private workflow: Workflow<any, Input, Output>,
     public history: HistoryStateEvent[],
     // TODO: properties used in the workflow should be encoded in the history to keep them constant between runs
     private propertyRetriever: PropertyRetriever,
     private eventualFactory: EventualFactory = createDefaultEventualFactory()
   ) {
+    this.historyCloned = deepClone(history);
     this.nextSeq = 0;
     this.expected = iterator(history, isCallEvent);
     this.events = iterator(history, isCompletionEvent);