build: Android's built-in Kotlin, the three plugins applying KGP themselves patched in third_party/

AGP 9 compiles Kotlin itself (android.builtInKotlin=true in every app),
and warns that applying the Kotlin Gradle Plugin will soon fail.
flutter_web_auth_2 5.1.0, keyboard_height_plugin 0.3.0 and flutter_tts
4.2.5 still apply it unconditionally, so their pub releases are copied
into third_party/ with only their android/build.gradle changed, and
the root overrides them by path (third_party/README.md says when to
drop each). The servers' images copy third_party/, as pub refuses an
override whose path is missing. third_party/ isn't our own code: left
out of the analysis and the format check.

All four apps' APKs build without the warning. A Kotlin daemon's
session file that slipped into Train's android/ goes, and every app's
android/.gitignore keeps .kotlin/ out.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

third_party/keyboard_height_plugin/android/build.gradle

@@ -0,0 +1,53 @@
+group 'com.nschairer.keyboard_height_plugin'
+version '1.0-SNAPSHOT'
+
+buildscript {
+    ext.kotlin_version = '2.1.0'
+    repositories {
+        google()
+        mavenCentral()
+    }
+
+    dependencies {
+        classpath 'com.android.tools.build:gradle:8.6.0'
+    }
+}
+
+allprojects {
+    repositories {
+        google()
+        mavenCentral()
+    }
+}
+
+apply plugin: 'com.android.library'
+
+android {
+    compileSdkVersion 34
+
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_1_8
+        targetCompatibility JavaVersion.VERSION_1_8
+    }
+
+
+    sourceSets {
+        main.java.srcDirs += 'src/main/kotlin'
+    }
+
+    defaultConfig {
+        minSdkVersion 16
+    }
+    if (project.android.hasProperty("namespace")) {
+        namespace 'com.nschairer.keyboard_height_plugin'
+    }
+}
+
+// Halkyon's patch (4 Nov 2026): Kotlin built into the Android Gradle plugin
+// (AGP 9, android.builtInKotlin=true) rather than the Kotlin Gradle plugin
+// applied here, as Flutter's guide for plugin authors has it.
+kotlin {
+    compilerOptions {
+        jvmTarget = org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_1_8
+    }
+}

third_party/keyboard_height_plugin/android/settings.gradle

@@ -0,0 +1 @@
+rootProject.name = 'keyboard_height_plugin'

third_party/keyboard_height_plugin/android/src/main/AndroidManifest.xml

@@ -0,0 +1,3 @@
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+  package="com.nschairer.keyboard_height_plugin">
+</manifest>

third_party/keyboard_height_plugin/android/src/main/kotlin/com/nschairer/keyboard_height_plugin/KeyboardHeightPlugin.kt

@@ -0,0 +1,93 @@
+package com.nschairer.keyboard_height_plugin
+import android.graphics.Rect
+import android.os.Build
+import androidx.annotation.NonNull
+import android.view.ViewTreeObserver
+import androidx.annotation.RequiresApi
+import io.flutter.embedding.engine.plugins.FlutterPlugin
+import io.flutter.plugin.common.EventChannel
+import io.flutter.embedding.engine.plugins.activity.ActivityAware
+import io.flutter.embedding.engine.plugins.activity.ActivityPluginBinding
+
+class KeyboardHeightPlugin : FlutterPlugin, EventChannel.StreamHandler, ActivityAware {
+    private val keyboardHeightEventChannelName = "keyboardHeightEventChannel"
+    private var eventSink: EventChannel.EventSink? = null
+    private var eventChannel: EventChannel? = null
+    private var activityPluginBinding: ActivityPluginBinding? = null
+
+    override fun onAttachedToEngine(@NonNull flutterPluginBinding: FlutterPlugin.FlutterPluginBinding) {
+        eventChannel = EventChannel(flutterPluginBinding.binaryMessenger, keyboardHeightEventChannelName)
+        eventChannel?.setStreamHandler(this)
+    }
+
+    override fun onDetachedFromEngine(@NonNull binding: FlutterPlugin.FlutterPluginBinding) {
+        eventChannel?.setStreamHandler(null)
+    }
+
+    override fun onListen(arguments: Any?, events: EventChannel.EventSink?) {
+        eventSink = events
+        val rootView = activityPluginBinding?.activity?.window?.decorView?.rootView
+        rootView?.viewTreeObserver?.addOnGlobalLayoutListener(object : ViewTreeObserver.OnGlobalLayoutListener {
+            override fun onGlobalLayout() {
+                val r = Rect()
+                rootView.getWindowVisibleDisplayFrame(r)
+
+                val screenHeight = rootView.height
+                val navigationBarHeight = getNavigationBarHeight();
+                var keypadHeight = screenHeight - r.bottom
+                if (isNavigationBarVisible()) {
+                    keypadHeight -= navigationBarHeight
+                }
+                val displayMetrics = activityPluginBinding?.activity?.resources?.displayMetrics
+                val logicalKeypadHeight = keypadHeight / (displayMetrics?.density ?: 1f)
+
+                if (keypadHeight > screenHeight * 0.15) {
+                    events?.success(logicalKeypadHeight.toDouble())
+                } else {
+                    events?.success(0.0)
+                }
+            }
+        })
+    }
+
+    override fun onCancel(arguments: Any?) {
+        eventSink = null
+    }
+
+    private fun getNavigationBarHeight(): Int {
+        val resourceId = activityPluginBinding?.activity?.resources?.getIdentifier("navigation_bar_height", "dimen", "android")
+        return if (resourceId != null && resourceId > 0) {
+            activityPluginBinding?.activity?.resources?.getDimensionPixelSize(resourceId) ?: 0
+        } else {
+            0
+        }
+    }
+
+    private fun isNavigationBarVisible(): Boolean {
+        val decorView = activityPluginBinding?.activity?.window?.decorView
+        val rootWindowInsets = decorView?.rootWindowInsets ?: return false
+        return if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
+            rootWindowInsets.isVisible(android.view.WindowInsets.Type.navigationBars())
+        } else {
+            val systemWindowInsetBottom = rootWindowInsets.systemWindowInsetBottom
+            systemWindowInsetBottom > 0
+        }
+    }
+    
+    // Implement ActivityAware methods
+    override fun onAttachedToActivity(binding: ActivityPluginBinding) {
+        activityPluginBinding = binding
+    }
+
+    override fun onDetachedFromActivityForConfigChanges() {
+        activityPluginBinding = null
+    }
+
+    override fun onReattachedToActivityForConfigChanges(binding: ActivityPluginBinding) {
+        activityPluginBinding = binding
+    }
+
+    override fun onDetachedFromActivity() {
+        activityPluginBinding = null
+    }
+}