ref(api)!: Remove legacy hybrid SDK facade

[philprime]

Description

Remove PrivateSentrySDKOnly completely now that supported hybrid SDKs use SentrySDK.internal and Objective-C consumers use SentryObjCSDK.internal. The legacy header, implementation, Objective-C runtime symbol, build references, dedicated tests, and test-plan entries are gone.

Implementation

• Centralize app-start callbacks and hybrid-mode state in SentrySDKInternal, with the structured app-start and performance APIs using that shared state.
• Move the remaining app-start serialization behavior into SentryInternalAppStartApi and use the structured internal APIs at SDK and test call sites.
• Keep SentryObjCPrivateSDKOnly as an independent SentryObjC compatibility surface, but delegate it directly to SentrySDK.internal rather than the removed class.
• Remove the legacy class from generated Sentry API snapshots and internalize supporting profiling headers.
• Reduce SENTRY-INTERNAL-API.md to an entry-point, source-navigation, architecture, and test-location guide instead of duplicating API declarations or migration history.

This intentionally removes the unsupported PrivateSentrySDKOnly source and runtime compatibility surface. All supported React Native, Flutter, .NET, and Unity integrations have migrated to the structured APIs.

#skip-changelog

Validation

• make format
• make analyze
• make generate-public-api
• make build-ios FOR_AGENTS=true
• make build-macos FOR_AGENTS=true
• make test-ios FOR_AGENTS=true, including 5,632 Sentry tests and 971 SentryV10 tests with zero failures

Local sample validation could not complete because the XCFramework sample artifacts were absent and the source sample encountered a stale duplicate-module cache conflict before compiling the changed sample source.

Checklist

• 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 supported 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.
• If I added a new public API, I also added it to the SentryObjC wrapper.

Closes #8908

[sentry]

📲 Install Builds

iOS

🔗 App Name	App ID	Version	Configuration
SDK-Size	io.sentry.sample.SDK-Size	9.27.0 (1)	Release

⚙️ sentry-cocoa Build Distribution Settings

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1238.71 ms	1263.40 ms	24.70 ms
Size	24.14 KiB	1.31 MiB	1.29 MiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
fc4e913	1231.79 ms	1267.89 ms	36.11 ms
6f28fd8	1229.98 ms	1271.73 ms	41.75 ms
a7c42d9	1217.25 ms	1253.98 ms	36.73 ms
230cc86	1225.33 ms	1258.67 ms	33.34 ms
5556249	1208.87 ms	1246.60 ms	37.72 ms
8ed81c1	1227.47 ms	1249.24 ms	21.77 ms
92fada5	1217.60 ms	1252.89 ms	35.30 ms
6d9f89d	1226.37 ms	1260.94 ms	34.57 ms
318f8af	1213.09 ms	1246.21 ms	33.13 ms
01ffe09	1208.52 ms	1240.94 ms	32.42 ms

App size

Revision	Plain	With Sentry	Diff
fc4e913	24.14 KiB	1.17 MiB	1.15 MiB
6f28fd8	24.14 KiB	1.30 MiB	1.28 MiB
a7c42d9	24.14 KiB	1.15 MiB	1.13 MiB
230cc86	24.14 KiB	1.25 MiB	1.23 MiB
5556249	24.14 KiB	1.29 MiB	1.27 MiB
8ed81c1	24.14 KiB	1.23 MiB	1.21 MiB
92fada5	24.14 KiB	1.17 MiB	1.15 MiB
6d9f89d	24.14 KiB	1.26 MiB	1.23 MiB
318f8af	24.14 KiB	1.30 MiB	1.28 MiB
01ffe09	24.14 KiB	1.29 MiB	1.27 MiB

Previous results on branch: philprime/remove-private-sdk-api

Startup times

Revision	Plain	With Sentry	Diff
5519155	1234.87 ms	1267.30 ms	32.43 ms
9b5a8b4	1220.10 ms	1263.90 ms	43.80 ms
1a8fbc1	1209.24 ms	1246.44 ms	37.19 ms
29c45c5	1230.60 ms	1264.31 ms	33.71 ms

App size

Revision	Plain	With Sentry	Diff
5519155	24.14 KiB	1.31 MiB	1.29 MiB
9b5a8b4	24.14 KiB	1.31 MiB	1.29 MiB
1a8fbc1	24.14 KiB	1.32 MiB	1.29 MiB
29c45c5	24.14 KiB	1.31 MiB	1.29 MiB

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