fix(replay): Improve error messages when compression worker fails to load (#19008)

Previously, when the compression worker failed to load (e.g., due to CSP
restrictions, network issues), Sentry captured a generic ErrorEvent with
almost no useful information ("Event: Event `Event` (type=error)").

This change wraps worker errors in descriptive Error objects that
explain
what failed and common causes, making debugging significantly easier.

Fixes JAVASCRIPT-337J

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
Co-authored-by: Andrei <168741329+andreiborza@users.noreply.github.com>
Co-authored-by: Andrei Borza <andrei.borza@sentry.io>

Author: 3 people

.size-limit.js

@@ -89,7 +89,7 @@ module.exports = [
     path: 'packages/browser/build/npm/esm/prod/index.js',
     import: createImport('init', 'browserTracingIntegration', 'replayIntegration', 'feedbackIntegration'),
     gzip: true,
-    limit: '98 KB',
+    limit: '99 KB',
   },
   {
     name: '@sentry/browser (incl. Feedback)',
@@ -208,7 +208,7 @@ module.exports = [
     name: 'CDN Bundle (incl. Tracing, Replay)',
     path: createCDNPath('bundle.tracing.replay.min.js'),
     gzip: true,
-    limit: '80 KB',
+    limit: '81 KB',
   },
   {
     name: 'CDN Bundle (incl. Tracing, Replay, Logs, Metrics)',

packages/replay-internal/src/eventBuffer/WorkerHandler.ts

@@ -33,7 +33,8 @@ export class WorkerHandler {
           if ((data as WorkerResponse).success) {
             resolve();
           } else {
-            reject();
+            DEBUG_BUILD && debug.warn('Received worker message with unsuccessful status', data);
+            reject(new Error('Received worker message with unsuccessful status'));
           }
         },
         { once: true },
@@ -42,7 +43,12 @@ export class WorkerHandler {
       this._worker.addEventListener(
         'error',
         error => {
-          reject(error);
+          DEBUG_BUILD && debug.warn('Failed to load Replay compression worker', error);
+          reject(
+            new Error(
+              `Failed to load Replay compression worker: ${error instanceof ErrorEvent && error.message ? error.message : 'Unknown error. This can happen due to CSP policy restrictions, network issues, or the worker script failing to load.'}`,
+            ),
+          );
         },
         { once: true },
       );