fix(android): Migrate workmanager_android to built-in Kotlin

.fvmrc

@@ -1,3 +1,3 @@
 {
-  "flutter": "3.44.8"
+  "flutter": "3.47.7"
 }

AGENTS.md

@@ -10,9 +10,9 @@ Code & test conventions (previously in `CLAUDE.md`) are consolidated in the last
 
 ## Android / AGP facts
 - AGP 9 enables built-in Kotlin **by default**; Flutter apps write `android.builtInKotlin=false` + `android.newDsl=false` in gradle.properties (flutter/flutter#183910).
-- The module must apply `kotlin-android` whenever built-in Kotlin is NOT active. Correct guard (same pattern as flutter_timezone):
-  `def builtInKotlin = agpMajor >= 9 && project.findProperty('android.builtInKotlin')?.toString() != 'false'`
-  Do NOT "simplify" this to `== 'true'`: an absent flag means built-in Kotlin is ON (AGP default), and applying KGP then throws.
+- The module never applies `kotlin-android`, not even behind a guard (built-in Kotlin migration, #743). When built-in Kotlin is NOT active, the Flutter Gradle Plugin applies KGP to plugins whose build file does not mention it. It decides that by regex over the build file text, so any `apply plugin: 'kotlin-android'` line, guarded or not, counts as "applies KGP": Flutter then skips its own apply and lists the plugin in its KGP warning (flutter/flutter#189770).
+  Configure the compiler only through the top-level `kotlin { compilerOptions { ... } }` block (works with built-in Kotlin and with KGP 2.0+).
+- The pubspec floor is Flutter 3.47.0, not the guide's 3.44: on every 3.44.x the FGP auto-apply ignores `android.builtInKotlin`, so with `android.builtInKotlin=true` it applies KGP to this module and AGP 9 fails the build ("The 'org.jetbrains.kotlin.android' plugin is no longer required for Kotlin support since AGP 9.0"). 3.47.0 is the first release that skips the auto-apply when built-in Kotlin is on. Apps on 3.44.x keep resolving 0.10.9.
 - `workmanager_android`'s build.gradle has no Flutter embedding dependency — the module can be built standalone (no Flutter SDK) to repro build issues. In real Flutter builds the FGP injects `io.flutter:flutter_embedding_debug`; `download.flutter.io` has a TLS cert mismatch (artifact only resolvable from the local Gradle cache), so standalone repros use `compileOnly` on the local engine `flutter.jar` + `androidx.core:core-ktx`, wired via an init script.
 - When building the plugin through the example app, the FGP relocates the plugin's build dir: unit test results land in `example/build/workmanager_android/`, **not** `workmanager_android/android/build/`. `./gradlew :workmanager_android:testDebugUnitTest` currently runs 50 tests.
 

example/android/gradle/wrapper/gradle-wrapper.properties

@@ -1,6 +1,6 @@
 #Fri May 30 01:37:19 JST 2025
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-8.13-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-9.3.1-all.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists

example/android/settings.gradle

@@ -18,8 +18,8 @@ pluginManagement {
 
 plugins {
     id "dev.flutter.flutter-plugin-loader" version "1.0.0"
-    id "com.android.application" version '8.11.0' apply false
-    id "org.jetbrains.kotlin.android" version "2.1.0" apply false
+    id "com.android.application" version '8.11.1' apply false
+    id "org.jetbrains.kotlin.android" version "2.3.20" apply false
 }
 
 include ":app"

workmanager_android/android/build.gradle

@@ -10,19 +10,6 @@ rootProject.allprojects {
 
 apply plugin: 'com.android.library'
 
-// AGP 9+ ships built-in Kotlin support and enables it by default; older
-// versions need the Kotlin Gradle Plugin (KGP) applied explicitly. Flutter
-// apps set `android.builtInKotlin=false` in gradle.properties
-// (flutter/flutter#183910) to keep the legacy KGP path working for
-// unmigrated plugins, so this module must apply KGP itself unless built-in
-// Kotlin is active. See #710 and #722.
-def agpMajor = com.android.Version.ANDROID_GRADLE_PLUGIN_VERSION.tokenize('.')[0] as int
-def builtInKotlin = agpMajor >= 9 &&
-    project.findProperty('android.builtInKotlin')?.toString() != 'false'
-if (!builtInKotlin) {
-    apply plugin: 'kotlin-android'
-}
-
 android {
     // Conditional for compatibility with AGP <4.2.
     if (project.android.hasProperty("namespace")) {
@@ -59,24 +46,16 @@ android {
         sourceCompatibility JavaVersion.VERSION_1_8
         targetCompatibility JavaVersion.VERSION_1_8
     }
-
-    if (agpMajor < 9) {
-        kotlinOptions {
-            tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).configureEach {
-                kotlinOptions.jvmTarget = "1.8"
-            }
-        }
-    }
 }
 
-// AGP 9: `kotlinOptions` inside `android {}` was removed. Configure the Kotlin
-// compiler via the `kotlin` extension (provided by built-in Kotlin, or by KGP
-// 2.0+ on the legacy path). Kept in sync with compileOptions above.
-if (agpMajor >= 9) {
-    kotlin {
-        compilerOptions {
-            jvmTarget = org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_1_8
-        }
+// Built-in Kotlin: this module does not apply the Kotlin Gradle Plugin (KGP).
+// AGP 9 compiles Kotlin itself; when built-in Kotlin is off (AGP < 9, or
+// `android.builtInKotlin=false`), the Flutter Gradle Plugin (Flutter 3.44+)
+// applies KGP to plugins that do not. See #743.
+// Kept in sync with compileOptions above.
+kotlin {
+    compilerOptions {
+        jvmTarget = org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_1_8
     }
 }
 

workmanager_android/pubspec.yaml

@@ -7,8 +7,8 @@ repository: https://github.com/fluttercommunity/flutter_workmanager
 issue_tracker: https://github.com/fluttercommunity/flutter_workmanager/issues
 
 environment:
-  sdk: '>=3.5.0 <4.0.0'
-  flutter: ">=3.38.0"
+  sdk: '>=3.13.0 <4.0.0'
+  flutter: ">=3.47.0"
 
 dependencies:
   flutter: