ci(android): gate name-based reachability on an R8-minified variant

R8 only ever ran on `release`, so every automated gate in this repository
exercised code the shipped APK does not contain. Reflective lookups, JNI
callbacks and native library loading can all break under shrinking while
`flutter test`, the Robolectric suites and `connectedDebugAndroidTest`
stay green — which is exactly how #1703 shipped, with the bundled FFmpeg
audio renderer shrunk out of release builds for TrueHD and DTS-HD.

Add a `minified` build type that inherits release's shrinker
configuration but stays debuggable and debug-signed, so it is an ordinary
test artifact and never a publishable one. Three integration details
took a run each to find: the Flutter plugin copies app build types into
every plugin module, so library-level shrinking deleted the plugin entry
points that only GeneratedPluginRegistrant references; the harness must
not be shrunk or the runner disappears; and androidx.test has to survive
in the app under test, or the runner cannot link its own supertype and
the run reports zero tests instead of failing.

Instrumentation still defaults to `debug`, because only one build type
can host androidTest and the existing playback suites drive media3
builder APIs the app never calls, which R8 shrinks legitimately. The new
reachability test opts into the minified variant instead and touches no
builder API, so the only keeps it depends on are the ones under test.
Emptying proguard-rules.pro was verified to fail it.

android/app/build.gradle.kts

@@ -391,8 +391,44 @@ android {
         debugSymbolLevel = "FULL"
       }
     }
+
+    // Instrumentation target that runs R8 (see testBuildType below).
+    //
+    // R8 only ever ran on `release`, so every gate in this repository exercised code
+    // the shipped APK does not contain: reflective lookups, JNI callbacks and native
+    // library loading can all break under shrinking while every debug check passes.
+    // #1703 shipped that way — DefaultRenderersFactory's Class.forName for the bundled
+    // FFmpeg audio renderer failed in release builds only.
+    //
+    // Inherits release's minification and keep rules (the Flutter plugin has already
+    // installed them by the time this block runs) but stays debuggable and debug-signed,
+    // so it is an ordinary test artifact and never a publishable one. Debuggable also
+    // makes the Flutter plugin treat it as debug mode, so it uses debug Dart artifacts.
+    create("minified") {
+      initWith(getByName("release"))
+      isDebuggable = true
+      // Resource shrinking is orthogonal to the reachability this variant guards and
+      // would only slow the instrumentation build down.
+      isShrinkResources = false
+      testProguardFiles("proguard-test-rules.pro")
+      proguardFile("proguard-instrumentation-rules.pro")
+      // Release has no signing config unless key.properties exists, which would leave
+      // this variant unsigned and uninstallable in CI.
+      signingConfig = signingConfigs.getByName("debug")
+      // Plugin subprojects only publish debug and release variants.
+      matchingFallbacks += listOf("debug", "release")
+      ndk {
+        debugSymbolLevel = "NONE"
+      }
+    }
   }
 
+  // Instrumentation normally runs against `debug`; the R8 reachability gate opts into the
+  // minified variant with -Pplezy.testBuildType=minified. Only one build type can host
+  // androidTest, and the existing playback suites need media3 builder APIs the app itself
+  // never calls — which R8 legitimately shrinks — so they stay on debug.
+  testBuildType = (findProperty("plezy.testBuildType") as String?) ?: "debug"
+
   packaging {
     jniLibs {
       // pickFirst only suppresses the duplicate libc++ merge error; the