feat(android-nav3): [Android Nav3 3] Track navigation state transitions

[0xadam-brown]

PR Stack (Android Nav3)

• feat(android-nav3): Android Nav3 integration #6128
• feat(android-nav3): [Android Nav3 1] Create the navigation3 module #6129
• feat(android-nav3): [Android Nav3 2] Model navigation routes #6130
• feat(android-nav3): [Android Nav3 3] Track navigation state transitions #6131
• feat(android-nav3): [Android Nav3 4] Introduce SentryNavEffect #6132

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📜 Description

Now we wire up the logic for consuming the host app's back stack and emitting finished Sentry data. The class responsible for doing so is BackStackObserver.

It rotates the ambient nav transaction and emits the following Sentry data every time the top of the back stack is updated:

• breadcrumbs
• screen names
• a projection of the host app back stack containing the most recent SentryNavOptions.maxCapturedBackStackEntries

BackStackObsever makes use of the RouteTranslator from #6130 for the actual back stack entry -> raw Sentry data translation.

💡 Motivation and Context

With route modeling in place, the next boundary is the state machine that reacts to navigation changes. Keeping that behavior separate makes it easier to review lifecycle and tracing semantics without mixing in Compose effect concerns yet.

addresses: JAVA-274

💚 How did you test it?

• Unit tests
• Manually via the (forthcoming) Nav3 sample app, including performance tests and macrobenchmarks

📝 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

Introduce the Compose-facing effect that owns this observer in application code.

#skip-changelog

⚠️ Merge this PR using a merge commit (not squash). Later PRs in the stack are based on this branch.

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📖	Do not forget to update Sentry-docs with your feature once the pull request gets approved.

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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

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[0xadam-brown]

Marked as experimental b/c this will be made public in a follow-on to the current PR stack (same below).

[0xadam-brown]

Marked as experimental b/c this will be made public in a follow-on to the current PR stack.

⚠️ Note that Nav3 currently only supports hints for breadcrumbs. The only other candidate is transactions, but I've refrained because Nav2 transactions lack them. Chime in if you think we should reconsider.