feat(telemetry): Capture failing resource URL on DOM event promise rejections

src/instrumentation-client.ts

@@ -36,6 +36,37 @@ Sentry.init({
     Sentry.consoleLoggingIntegration(),
   ],
 
+  // When a Chrome promise rejection is fired by a resource load failure, the
+  // rejection reason is the DOM Event whose target is the HTML element that
+  // failed (e.g. a <link> stylesheet). Without extra instrumentation, the
+  // serialised event shows only "[object HTMLLinkElement]" and gives no clue
+  // which URL caused the failure. This hook extracts the resource URL and
+  // adds it as a searchable tag and as extra context so we can identify the
+  // failing asset.
+  beforeSend: (event, hint) => {
+    const originalException = hint?.originalException;
+    if (
+      originalException instanceof Event &&
+      originalException.target instanceof HTMLElement
+    ) {
+      const target = originalException.target as HTMLElement & {
+        href?: string;
+        src?: string;
+      };
+      const resourceUrl = target.href ?? target.src ?? target.tagName;
+      event.tags = {
+        ...event.tags,
+        failing_resource_url: resourceUrl,
+        failing_resource_tag: target.tagName.toLowerCase(),
+      };
+      event.extra = {
+        ...event.extra,
+        failing_resource_element: target.outerHTML?.slice(0, 300),
+      };
+    }
+    return event;
+  },
+
   // Filter sensitive metric attributes (no PII in metrics)
   beforeSendMetric: metric => {
     // Remove any accidentally added PII attributes