Native crash autocapture double-reports fatal React Native JS errors (JavascriptException) #567

Problem

When the React Native SDK enables native crash autocapture (@posthog/react-native-plugin, errorTracking.autocapture.nativeCrashes, see PostHog/posthog-js#3677), a fatal JS error can be captured twice:

1. The JS layer captures it via uncaughtExceptions autocapture (with the JS stack trace), and
2. React Native rethrows fatal JS errors on the native side as a com.facebook.react.common.JavascriptException on the main thread. posthog-android's uncaught-exception handler then captures it as a separate native crash (with a native stack trace).

The result is two $exception events for one logical error.

Suggested fix

posthog-android should expose a way to ignore exceptions that originate from React Native's fatal-JS path, and/or skip reporting throwables of type com.facebook.react.common.JavascriptException, so the JS-captured event is the single source of truth.

For reference, sentry-react-native does exactly this on the native side:

// React native internally throws a JavascriptException.
// we want to ignore it on the native side to avoid sending it twice.
options.addIgnoredExceptionForType(JavascriptException.class);

(https://github.com/getsentry/sentry-react-native/blob/f170ec355cd622d3e935478a23660ad4cb97e896/packages/core/android/src/main/java/io/sentry/react/RNSentryStart.java#L355)

Notes

• This pairs with the iOS equivalent (sibling issue in posthog-ios: Native crash autocapture double-reports fatal React Native JS errors (RCTFatalException) posthog-ios#653).
• Worth verifying empirically against current RN (0.79+) release builds, since the exact rethrow path can change between RN versions.
• Discovered while reviewing feat(react-native): add native crash capture and debug symbol upload posthog-js#3677.