Events should not be added to queue if event loop is not started. (#8640)

Author: bbastings

common/api/core-frontend.api.md

@@ -4941,6 +4941,8 @@ export class IModelApp {
     static get hasRenderSystem(): boolean;
     static get hubAccess(): FrontendHubAccess | undefined;
     static get initialized(): boolean;
+    // @internal
+    static get isEventLoopStarted(): boolean;
     static get localization(): Localization;
     // (undocumented)
     static get locateManager(): ElementLocateManager;

common/changes/@itwin/core-frontend/check-event-loop-started_2025-10-15-15-20.json

@@ -0,0 +1,10 @@
+{
+  "changes": [
+    {
+      "packageName": "@itwin/core-frontend",
+      "comment": "",
+      "type": "none"
+    }
+  ],
+  "packageName": "@itwin/core-frontend"
+}

core/frontend/src/IModelApp.ts

@@ -525,6 +525,11 @@ export class IModelApp {
       }, IModelApp.animationInterval.milliseconds);
   }
 
+  /** Return true if the main event processing loop has been started.
+   * @internal
+   */
+  public static get isEventLoopStarted() { return IModelApp._wantEventLoop; }
+
   /** @internal */
   public static startEventLoop() {
     if (!IModelApp._wantEventLoop) {

core/frontend/src/tools/ToolAdmin.ts

@@ -790,6 +790,10 @@ export class ToolAdmin {
    * @internal
    */
   public static addEvent(ev: Event, vp?: ScreenViewport): void {
+    // Don't add events to queue if event loop hasn't been started to process them...
+    if (!IModelApp.isEventLoopStarted)
+      return;
+
     if (!ToolAdmin.tryReplace(ev, vp)) // see if this event replaces the last event in the queue
       this._toolEvents.push({ ev, vp }); // otherwise put it at the end of the queue.