perf(core): [SDK Overhead Reduction 9] Lazily allocate reflection serializer state

[adinauer]

PR Stack (SDK Overhead Reduction)

• perf(core): SDK Overhead Reduction #5499
• perf(core): [SDK Overhead Reduction 1] Skip java.specification.version lookup on Android #5500
• perf(android): [SDK Overhead Reduction 2] Replace reflective OptionsContainer with direct subclass #5501
• perf(android): [SDK Overhead Reduction 3] Reuse SentryExecutorService for DeviceInfoUtil pre-caching #5502
• perf(android): [SDK Overhead Reduction 4] Use default timezone directly #5587
• perf(core): [SDK Overhead Reduction 5] Replace Calendar with Date in DateUtils #5589
• perf(core): [SDK Overhead Reduction 6] Reduce JsonWriter stack allocation #5591
• perf(core): [SDK Overhead Reduction 7] Lazily allocate Breadcrumb data #5598
• perf(core): [SDK Overhead Reduction 8] Reduce context serialization allocations #5599
• perf(core): [SDK Overhead Reduction 9] Lazily allocate reflection serializer state #5600
• perf(core): [SDK Overhead Reduction 10] Lazily create reflection JSON serializer #5601
• perf(core): [SDK Overhead Reduction 11] Replace ISO8601 timestamp handling #5602

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📜 Description

Lazily creates the JsonReflectionObjectSerializer visiting set only when reflection serialization is used.

The set still tracks objects during reflection serialization for cyclic reference and max-depth handling, but normal JSON serialization paths no longer allocate it eagerly.

💡 Motivation and Context

Most SDK payloads serialize through explicit JsonSerializable implementations or other supported direct types. Those paths do not need reflection cycle tracking, so allocating an empty HashSet for every reflection serializer adds unnecessary overhead.

💚 How did you test it?

• ./gradlew :sentry:test --tests io.sentry.JsonReflectionObjectSerializerTest --tests io.sentry.JsonObjectSerializerTest
• ./gradlew spotlessApply apiDump
• Re-ran ./gradlew :sentry:test --tests io.sentry.JsonReflectionObjectSerializerTest --tests io.sentry.JsonObjectSerializerTest

📝 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

#skip-changelog

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

[sentry]

📲 Install Builds

Android

🔗 App Name	App ID	Version	Configuration
SDK Size	io.sentry.tests.size	8.43.1 (1)	release

⚙️ sentry-android Build Distribution Settings

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	340.48 ms	427.56 ms	87.08 ms
Size	0 B	0 B	0 B