eventLoopBlockIntegration: breadcrumbs are dropped from EventLoopBlocked events (Scope.update() ignores the breadcrumbs field)

[beyondkmp]

Summary

Breadcrumbs are silently dropped from EventLoopBlocked events sent by eventLoopBlockIntegration (from @sentry/node-native) because Scope.update() does not copy the breadcrumbs field from a plain scope-data object.

Reproduction

const Sentry = require('@sentry/node');
const { eventLoopBlockIntegration } = require('@sentry/node-native');

Sentry.init({
  dsn: '__YOUR_DSN__',
  integrations: [eventLoopBlockIntegration({ threshold: 1000 })],
});

Sentry.addBreadcrumb({ category: 'test', message: 'breadcrumb before block', level: 'info' });

// 1. Sanity check: a normal event DOES include the breadcrumb
Sentry.captureException(new Error('normal event'));

// 2. Block the event loop past the threshold to trigger an EventLoopBlocked event
setTimeout(() => {
  const end = Date.now() + 3000;
  while (Date.now() < end) { /* busy loop */ }
}, 2000);

Root cause

In the watchdog worker (packages/node-native/src/event-loop-block-watchdog.ts), the scope is reconstructed like this:

const scope = crashedThread.pollState?.scope
  ? new Scope().update(crashedThread.pollState.scope).getScopeData()
  : new Scope().getScopeData();
applyScopeToEvent(event, scope);

Scope.update() in @sentry/core only copies tags, attributes, extra, user, contexts, level, fingerprint, propagationContext, and conversationId — it never reads breadcrumbs or attachments. The fresh Scope retains its empty _breadcrumbs, so applyScopeToEvent overwrites the event's breadcrumbs with undefined.

The same round-trip also drops attachments.

Suggested fix

The safest targeted fix is to carry breadcrumbs (and attachments) over explicitly after reconstructing the scope in event-loop-block-watchdog.ts, similar to what the old anrIntegration worker did:

const scope = crashedThread.pollState?.scope
  ? new Scope().update(crashedThread.pollState.scope).getScopeData()
  : new Scope().getScopeData();
scope.breadcrumbs = crashedThread.pollState?.scope?.breadcrumbs ?? [];

Environment

• @sentry/electron: 7.15.0
• @sentry/node-native: 10.62.0
• @sentry/core: 10.62.0
• Electron: 40

[linear-code]

ELECTR-56

JS-3064

[sentry-pierre]

I cleaned this up so the analysis doesn't have to compete with the template scaffolding.

What I checked:

• src/native/event-loop-blocked-integration.ts in this repo is just a thin wrapper; the scope-reconstruction bug is in @sentry/node-native / @sentry/core upstream.
• Because the fix needs to land in getsentry/sentry-javascript, a maintainer may want to transfer this issue there.

A maintainer can take it from here.

[sentry-pierre]

I confirmed the bug in packages/node-native/src/event-loop-block-watchdog.ts. The scope reconstruction via new Scope().update(pollState.scope) silently drops both breadcrumbs and attachments because Scope.update() in @sentry/core only copies tags, attributes, extra, user, contexts, level, fingerprint, propagationContext, and conversationId from plain objects.

For comparison, the older ANR worker in packages/node-core/src/integrations/anr/worker.ts sidesteps this by passing the raw ScopeData straight to applyScopeDataToEvent.

A cleaner fix than the suggested patch is to merge the raw pollState.scope into a fresh default ScopeData with mergeScopeData — that preserves breadcrumbs, attachments, and any other fields the round-trip currently strips.

[github-actions]

A PR closing this issue has just been released 🚀

This issue was referenced by PR #22322, which was included in the 10.67.0 release.