fix(core): [Callback Errors 1] Report callback failures

[adinauer]

PR Stack (Callback Errors)

• fix(core): Handle callback errors #6140
• fix(core): [Callback Errors 1] Report callback failures #6141
• fix(core): [Callback Errors 2] Drop failed processor data #6142
• fix(core): [Callback Errors 3] Drop failed breadcrumbs #6143

---

📜 Description

Adds DiscardReason.CALLBACK_ERROR and uses it when an existing beforeSend* callback throws and drops telemetry. Intentional null returns continue to use before_send.

The change preserves transaction/root-span and log/metric byte accounting, and exposes the new reason through OnDiscardCallback.

💡 Motivation and Context

Callback failures and intentional filtering currently share the same discard reason. Distinguishing them makes client reports and local discard observers accurately describe why telemetry was dropped.

• 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.clientreport.ClientReportTest
• ./gradlew :sentry:apiCheck

📝 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 next stack PR changes event processor exception handling.

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

[github-actions]

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Instructions and example for changelog

Please add an entry to CHANGELOG.md to the "Unreleased" section. Make sure the entry includes this PR's number.

Example:

## Unreleased

### Fixes

- [Callback Errors 1] Report callback failures ([#6141](https://github.com/getsentry/sentry-java/pull/6141))

If none of the above apply, you can opt out of this check by adding #skip-changelog to the PR description or adding a skip-changelog label.

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[sentry]

📲 Install Builds

Android

🔗 App Name	App ID	Version	Configuration
SDK Size	io.sentry.tests.size	8.57.0 (1)	release

⚙️ sentry-android Build Distribution Settings