fix(core): Prevent infinite recursion when event processor throws

packages/core/src/utils/prepareEvent.ts

@@ -11,6 +11,7 @@ import { addExceptionMechanism, uuid4 } from './misc';
 import { normalize } from './normalize';
 import { applyScopeDataToEvent, getCombinedScopeData } from './scopeData';
 import { truncate } from './string';
+import { resolvedSyncPromise } from './syncpromise';
 import { dateTimestampInSeconds } from './time';
 
 /**
@@ -93,7 +94,11 @@ export function prepareEvent(
     ...data.eventProcessors,
   ];
 
-  const result = notifyEventProcessors(eventProcessors, prepared, hint);
+  // Skip event processors for internal exceptions to prevent recursion
+  const isInternalException = hint.data && (hint.data as { __sentry__: boolean }).__sentry__ === true;
+  const result = isInternalException
+    ? resolvedSyncPromise(prepared)
+    : notifyEventProcessors(eventProcessors, prepared, hint);
 
   return result.then(evt => {
     if (evt) {

packages/core/test/lib/client.test.ts

@@ -2007,6 +2007,31 @@ describe('Client', () => {
       });
     });
 
+    test('client-level event processor that throws on all events does not cause infinite recursion', () => {
+      const options = getDefaultTestClientOptions({ dsn: PUBLIC_DSN });
+      const client = new TestClient(options);
+
+      let processorCallCount = 0;
+      // Add processor at client level - this runs on ALL events including internal exceptions
+      client.addEventProcessor(() => {
+        processorCallCount++;
+        throw new Error('Processor always throws');
+      });
+
+      client.captureMessage('test message');
+
+      // Should be called once for the original message
+      // internal exception events skips event processors entirely.
+      expect(processorCallCount).toBe(1);
+
+      // Verify the processor error was captured and sent
+      expect(TestClient.instance!.event!.exception!.values![0]).toStrictEqual({
+        type: 'Error',
+        value: 'Processor always throws',
+        mechanism: { type: 'internal', handled: false },
+      });
+    });
+
     test('records events dropped due to `sampleRate` option', () => {
       expect.assertions(1);