fix(core): [Callback Errors 3] Drop failed processor data

[adinauer]

PR Stack (Callback Errors)

• fix(core): Handle callback errors #6140
• fix(core): [Callback Errors 1] Report callback failures #6141
• ref(core): [Callback Errors 2] Mark SDK-owned event processors #6162
• fix(core): [Callback Errors 3] Drop failed processor data #6142
• fix(core): [Callback Errors 4] Drop failed breadcrumbs #6143
• fix(core): [Callback Errors 5] Handle tracesSampler failures #6163
• fix(core): [Callback Errors 6] Handle profilesSampler failures #6164
• fix(core): [Callback Errors 7] Handle replay sampling failures #6165
• fix(core): [Callback Errors 8] Report dropped profiles #6166
• fix(integrations): [Callback Errors 9] Guard custom callbacks #6167
• feat(callbacks): [Callback Errors Optional Addon] Add opt-in strict callback mode #6173

---

📜 Description

Drops the current telemetry item when a customer EventProcessor throws. Subsequent processors and beforeSend* callbacks do not run, and the item is not sent or added to a batch.

SDK-owned processors are identified by the internal SentryEventProcessor marker from #6162. Their exceptions are logged, but processing continues with the current item, including subsequent processors and beforeSend* callbacks. No callback_error client-report outcome or OnDiscardCallback notification is emitted for an SDK processor failure because the item is not dropped.

Customer processor exceptions record callback_error outcomes for errors, transactions and spans, replays, feedback, logs and log bytes, and metrics and metric bytes. Intentional processor null results continue to use event_processor, including for SDK-owned processors. Existing accounting for spans actually removed by a processor is preserved.

The distinction applies regardless of registration through options or scope. Replay processors only run from options. The marker identifies the implementation hierarchy; customer subclasses of SDK processors inherit the marker.

💡 Motivation and Context

Continuing after a customer processor failure can send partially processed data, including data that the processor intended to scrub. Fail closed for customer code while preserving the existing continue-on-error behavior for SDK-owned processors. Client reports represent discarded telemetry, not internal exceptions that do not cause a drop.

• refs: Align callback error handling with other SDKs #6081

💚 How did you test it?

• ./gradlew spotlessApply apiDump
• ./gradlew :sentry:test --tests io.sentry.SentryClientTest --tests io.sentry.SentryClientInternalEventProcessorTest --tests io.sentry.ScopeTest --tests io.sentry.ScopesTest --tests io.sentry.clientreport.ClientReportTest --tests io.sentry.internal.eventprocessor.SentryEventProcessorTest :sentry:apiCheck :sentry:spotlessCheck — 588 tests passed
• Added regression coverage for SDK failures across all six processing paths, scope/options registration, subsequent processors and callbacks, transport/batch delivery, error logging, and absence of discard accounting.
• Verified customer failures still drop data, SDK processors returning null still drop intentionally, and actual span removals retain their accounting. Before the SDK-specific guards, 15 new regression cases failed; all pass with the change.

📝 Checklist

• I added GH Issue ID & Linear ID
• I added tests to verify the changes.
• No new PII added or SDK only sends newly added PII if sendDefaultPII is enabled.
• I updated the docs if needed.
• I updated the wizard if needed.
• Review from the native team if needed.
• No breaking change or entry added to the changelog.
• No breaking change for hybrid SDKs or communicated to hybrid SDKs.
• Public API changes reviewed by another Mobile SDK team member or implemented according to the develop docs spec.

🔮 Next steps

The final stack PR changes beforeBreadcrumb exception handling. Profile/replay artifact cleanup and profile discard accounting remain separate follow-ups; this update only distinguishes SDK-owned and customer processors. Existing catch types are unchanged.

⚠️ Merge this PR using a merge commit (not squash). Only the collection branch is squash-merged into main.

[github-actions]

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## Unreleased

### Fixes

- [Callback Errors 3] Drop failed processor data ([#6142](https://github.com/getsentry/sentry-java/pull/6142))

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📲 Install Builds

Android

🔗 App Name	App ID	Version	Configuration
SDK Size	io.sentry.tests.size	8.59.0 (1)	release

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