feat(extend-app-start): [2/4] Add deferred extended span and extension state

[buenaflor]

PR Stack (Extend App Start)

• feat(extend-app-start): App start extension API #5604
• feat(extend-app-start): [1/4] Add IAppStartExtender bridge #5605
• feat(extend-app-start): [2/4] Add deferred extended span and extension state #5606
• feat(extend-app-start): [3/4] Materialize extended app start span and extend the vital #5608

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📜 Description

Builds the Android machinery behind the IAppStartExtender bridge:

• ExtendedAppStartSpan — a deferred ISpan created in Application.onCreate, before the app start transaction exists. Pre-materialization, calls delegate to NoOpSpan and finish(...) buffers the status + call-time timestamp; materialize(realChild) swaps in the real child span and replays a buffered finish. Idempotent.
• AppStartMetrics implements IAppStartExtender — extendAppStart() (guarded against already-extended / measurements-sent / activity-created / first-frame-drawn), finishAppStart(), getExtendedAppStartSpan(), plus accessors used by the next PR (isExtendedAppStartPending, getPendingExtendedAppStartSpan, markExtendedAppStartMaterialized) and a deadline-aware getExtendedAppStartEndTime() (returns null on DEADLINE_EXCEEDED so the vital is suppressed rather than inflated). clear() resets the new state.
• Registered via AndroidOptionsInitializer.

Still inert end-to-end: nothing materializes the span yet (next PR wires ActivityLifecycleIntegration + the vital), and the public Sentry facade lands last.

💡 Motivation and Context

Second PR of the stack implementing the app start extension API (part of #5553).

💚 How did you test it?

Unit tests (TDD):

• ExtendedAppStartSpanTest (8 cases) — buffering, materialize replay, delegation, start-date, idempotency.
• AppStartMetricsTest (11 new cases) — extend creates a pending span; guards warn + ignore; finish idempotency; user-finish vs deadline reflected in the end-time accessor; clear() resets.

./gradlew :sentry-android-core:apiCheck, spotless, and AndroidOptionsInitializerTest (init wiring) pass.

📝 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.

🔮 Next steps

[3/4] — materialize the span across the three transaction paths in ActivityLifecycleIntegration and extend/suppress the app start vital in PerformanceAndroidEventProcessor.

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

#skip-changelog

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[sentry]

📲 Install Builds

Android

🔗 App Name	App ID	Version	Configuration
SDK Size	io.sentry.tests.size	8.44.1 (1)	release

⚙️ sentry-android Build Distribution Settings

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Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	311.84 ms	365.94 ms	54.10 ms
Size	0 B	0 B	0 B

Baseline results on branch: feat/app-start-extension-core

Startup times

Revision	Plain	With Sentry	Diff
3d04aae	324.42 ms	359.30 ms	34.88 ms
69d43cc	380.70 ms	424.90 ms	44.20 ms
2821a4d	315.46 ms	366.56 ms	51.10 ms

App size

Revision	Plain	With Sentry	Diff
3d04aae	0 B	0 B	0 B
69d43cc	0 B	0 B	0 B
2821a4d	0 B	0 B	0 B

Previous results on branch: feat/app-start-extension-android

Startup times

Revision	Plain	With Sentry	Diff
b76203f	336.02 ms	403.42 ms	67.40 ms

App size

Revision	Plain	With Sentry	Diff
b76203f	0 B	0 B	0 B