Remove the AGP 9 opt-outs once react-native-test-app supports them

從 apps/test-app/android/gradle.properties 和 packages/host/android/build.gradle 開始，接著檢查所引用的 react-native-test-app Android Gradle 檔案以及兩個遷移阻礙。驗證 host 模組針對新 DSL 的變更，同時保留其針對 built-in-Kotlin 的條件行為，並執行 Android 測試應用程式的設定與安裝檢查。完成標準是移除兩個 opt-out，且在上游阻礙解決後測試應用程式仍能完成設定與安裝。

The test app sets both AGP 9 opt-outs in apps/test-app/android/gradle.properties:

android.builtInKotlin=false
android.newDsl=false

This issue tracks removing them. Both are blocked on react-native-test-app, not on us.

Correction. An earlier revision of this issue said we were "already off the sibling flag" and running built-in Kotlin natively. That was wrong — we tried it, the Android build failed, and #372 had to put android.builtInKotlin=false back. Details in blocker 1.

Deadline

Per Android's DSL/API migration timeline, AGP 10.0 (estimated late 2026) removes both opt-outs, along with the legacy APIs. Once React Native pins an AGP 10 these flags stop being a choice — the build either has migrated or it doesn't configure. That is plausibly one or two React Native minors away, so this is a when, not an if.

Blocker 1: built-in Kotlin — sources added via java.srcDirs are not compiled

react-native-test-app's app module adds its version-specific sources with main.java.srcDirs += [...]. The Kotlin plugin adds those directories to the Kotlin source set; AGP's built-in Kotlin only picks up the standard ones. Building with the flag unset (react-native-test-app 5.4.8, React Native 0.88 nightly, AGP 9.2.1) fails :app:compileReleaseKotlin:

e: ComponentActivity.kt:33:9 Unresolved reference 'ComponentActivityDelegate'
e: MainActivity.kt:145:9 Unresolved reference 'testApp'
e: MainActivity.kt:225:50 Unresolved reference 'reactHost'
e: MainActivity.kt:135:17 Unresolved reference 'canUseCamera'
e: MainActivity.kt:25:45 Unresolved reference 'ComponentBottomSheetDialogFragment'

Every unresolved symbol lives in an added directory — src/reactactivitydelegate-0.75/java, src/reactapplication-0.76/java, src/reacthost-0.76/java, src/camera/java. Files under the standard src/main/java compile fine. Their useBuiltInKotlin gate avoids applying the Kotlin plugin on top of built-in Kotlin, but the module still needs that plugin to compile at all.

Likely fix upstream: add the same directories to main.kotlin.srcDirs.

Our own half is already done. react-native-node-api applies the Kotlin plugin only when built-in Kotlin is unavailable, so the published library works under either regime no matter what the harness needs. That shipped in #372 and waits on nothing.

Blocker 2: the new DSL

Both react-native-test-app modules still use the old DSL, permalinked at 5.4.8:

Location	Old DSL
android/app/build.gradle#L77	compileSdkVersion
android/app/build.gradle#L88	kotlinOptions (gated on !useBuiltInKotlin)
android/app/build.gradle#L95-L96	minSdkVersion, targetSdkVersion
android/app/build.gradle#L161	lintOptions
android/support/build.gradle#L16	compileSdkVersion
android/support/build.gradle#L19-L20	minSdkVersion, targetSdkVersion

packages/host/android/build.gradle is old DSL too, and this half is ours. It matters beyond our CI: it is the published library, so it has to be new-DSL clean before consumers can migrate — the same shape as the built-in Kotlin problem that file already solves.

• #L52, #L69 — script-style apply plugin: instead of a plugins {} block
• #L101 — compileSdkVersion
• #L109-L110 — minSdkVersion, targetSdkVersion
• #L154 — lintOptions

Ordering

The flags are coupled one way: builtInKotlin=false requires newDsl=false, because the Kotlin plugin is incompatible with the new DSL. So blocker 1 has to be resolved before blocker 2 can be — though each piece of work is independently useful, and our own module can move to the new DSL at any time.

Nothing upstream tracks either blocker yet. Whether to file it, and the paste-ready text, is #390.

Done when

Both lines are gone from apps/test-app/android/gradle.properties and the Android test app still configures and installs.

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Introduced by #372. Links into this repo point at main and are accurate as of that PR merging.