build: add reproducible Android release verification

Pin Gradle inputs and dependency metadata, then enforce analyze, lint, build, R8, immutability, and focused regression gates in CI.

android/app/build.gradle.kts

@@ -1,12 +1,18 @@
 import java.util.Properties
 import java.io.File
 import java.io.FileInputStream
+import java.security.MessageDigest
 
 plugins {
     id("com.android.application")
     id("dev.flutter.flutter-gradle-plugin")
 }
 
+fun sha256Hex(file: File): String {
+    val digest = MessageDigest.getInstance("SHA-256").digest(file.readBytes())
+    return digest.joinToString("") { "%02x".format(it.toInt() and 0xff) }
+}
+
 val projectRootDir = rootProject.projectDir.parentFile
 val localPropertiesFile = rootProject.file("local.properties")
 val localProperties = Properties().apply {
@@ -140,10 +146,6 @@ android {
         targetCompatibility = JavaVersion.VERSION_17
     }
 
-    packaging {
-        resources.excludes.add("META-INF/**")
-    }
-
     val keystorePropertiesFile = rootProject.file("key.properties")
     val keystoreProperties = Properties()
     if (keystorePropertiesFile.exists()) {
@@ -156,6 +158,68 @@ android {
         admobProperties.load(FileInputStream(admobPropertiesFile))
     }
 
+    // Explicit opt-in used only by GitHub Actions to exercise the real
+    // release/R8 graph. Production release signing and config pinning remain
+    // fail-closed outside that CI smoke path.
+    val ciReleaseSmoke =
+        System.getenv("GITHUB_ACTIONS") == "true" &&
+            System.getenv("REVOLT_CI_RELEASE_SMOKE") == "true"
+
+    val appConfigFile = rootProject.file("../lib/logic/app_config.dart")
+    val verifyReleaseAppConfig = tasks.register("verifyReleaseAppConfig") {
+        group = "verification"
+        description = "Verify the production Dart app config against REVOLT_APP_CONFIG_SHA256."
+        doLast {
+            if (ciReleaseSmoke) {
+                logger.lifecycle("Skipping production app-config pin for CI release smoke build")
+                return@doLast
+            }
+
+            val expected = System.getenv("REVOLT_APP_CONFIG_SHA256")?.trim()?.lowercase()
+            if (expected.isNullOrEmpty()) {
+                throw org.gradle.api.GradleException(
+                    "REVOLT_APP_CONFIG_SHA256 is required for production release builds"
+                )
+            }
+            if (!Regex("[0-9a-f]{64}").matches(expected)) {
+                throw org.gradle.api.GradleException(
+                    "REVOLT_APP_CONFIG_SHA256 must be exactly 64 lowercase hexadecimal characters"
+                )
+            }
+            if (!appConfigFile.isFile) {
+                throw org.gradle.api.GradleException(
+                    "Production app config is missing: ${appConfigFile.absolutePath}"
+                )
+            }
+
+            val configText = appConfigFile.readText()
+            val templateMarkers = listOf(
+                "'0.0.0.0'",
+                "YOUR_DOMAIN",
+                "YOUR_GITHUB_USERNAME",
+                "YOUR_REPO_NAME",
+                "ca-app-pub-0000000000000000/0000000000",
+            )
+            val remainingMarker = templateMarkers.firstOrNull(configText::contains)
+            if (remainingMarker != null) {
+                throw org.gradle.api.GradleException(
+                    "Production app config still contains template marker: $remainingMarker"
+                )
+            }
+
+            val actual = sha256Hex(appConfigFile)
+            if (actual != expected) {
+                throw org.gradle.api.GradleException(
+                    "Production app config SHA-256 mismatch: expected $expected, got $actual"
+                )
+            }
+        }
+    }
+
+    tasks.matching { it.name == "preReleaseBuild" }.configureEach {
+        dependsOn(verifyReleaseAppConfig)
+    }
+
     defaultConfig {
         applicationId = "com.paladinvpn.app"
         minSdk = flutter.minSdkVersion
@@ -176,7 +240,11 @@ android {
 
     buildTypes {
         release {
-            signingConfig = signingConfigs.getByName("release")
+            signingConfig = if (ciReleaseSmoke) {
+                signingConfigs.getByName("debug")
+            } else {
+                signingConfigs.getByName("release")
+            }
             isMinifyEnabled = true
             isShrinkResources = true
             proguardFiles(