diff --git a/.github/workflows/debug.yml b/.github/workflows/debug.yml
index e133a5e6d9..a02b182238 100644
--- a/.github/workflows/debug.yml
+++ b/.github/workflows/debug.yml
@@ -228,8 +228,15 @@ jobs:
       - name: Assemble Universal APK
         run: |
           echo "gradle_time_start=$(date +%s)" >> $GITHUB_ENV
-          flox activate -d flox/base -- ./gradlew :app:assembleV8Debug --no-daemon
+          set -o pipefail
+          flox activate -d flox/base -- ./gradlew :app:assembleV8Debug --no-daemon 2>&1 | tee "$RUNNER_TEMP/assemble.log"
           echo "gradle_time_end=$(date +%s)" >> $GITHUB_ENV
+          # D8 logs this (non-fatal) once per class when the pinned R8 is older than the Kotlin
+          # metadata version, burying every real diagnostic. See the `r8` pin in libs.versions.toml.
+          if grep -q "Unexpected error during rewriting of Kotlin metadata" "$RUNNER_TEMP/assemble.log"; then
+            echo "::error::D8 could not rewrite Kotlin metadata. Most likely the R8 pinned in gradle/libs.versions.toml is older than the Kotlin metadata version (bump 'r8'), or the pin no longer takes effect on the build classpath. See ADFA-6822."
+            exit 1
+          fi
 
 
       - name: Find APK file
diff --git a/build.gradle.kts b/build.gradle.kts
index 15a7836cc3..06e157dd22 100755
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -62,6 +62,8 @@ jacoco {
 
 buildscript {
 	dependencies {
+		// Must stay first: pins a D8/R8 that understands the Kotlin metadata version (ADFA-6822).
+		classpath(libs.android.r8)
 		classpath(libs.kotlin.gradle.plugin)
 		classpath(libs.nav.safe.args.gradle.plugin)
 	}
diff --git a/gradle/libs.versions.toml b/gradle/libs.versions.toml
index 3ca884d690..cdc27caaf2 100644
--- a/gradle/libs.versions.toml
+++ b/gradle/libs.versions.toml
@@ -19,6 +19,7 @@ gson = "2.10.1"
 junit-jupiter = "5.10.2"
 anroidx-test-core = "2.2.0"
 koinAndroid = "4.1.1"
+# A Kotlin minor bump may need a newer `r8` (see its entry below, ADFA-6822).
 kotlin = "2.3.0"
 kotlin-coroutines = "1.9.0"
 kotlinxCoroutinesCore = "1.10.2"
@@ -37,6 +38,9 @@ ksp = "2.3.6"
 antlr4 = "4.13.1"
 androidx-work = "2.10.0"
 androidx-espresso = "3.5.1"
+# Pinned ahead of AGP on the root buildscript classpath: AGP 8.8.2's bundled D8 8.8.34 cannot rewrite
+# Kotlin 2.3 metadata. Bump with `kotlin`; remove once AGP is upgraded (ADFA-6837).
+r8 = "8.13.25"
 retrofit = "2.11.0"
 markwon = "4.6.2"
 maven-publish-plugin = "0.27.0"
@@ -324,6 +328,7 @@ tooling-slf4j = { module = "org.slf4j:slf4j-api", version = "2.0.17" }
 snakeyaml-engine = { module = "org.snakeyaml:snakeyaml-engine", version = "2.10" }
 
 # Classpaths
+android-r8 = { module = "com.android.tools:r8", version.ref = "r8" }
 android-gradle-plugin = { module = "com.android.tools.build:gradle", version.ref = "agp" }
 kotlin-gradle-plugin = { module = "org.jetbrains.kotlin:kotlin-gradle-plugin", version.ref = "kotlin" }
 nav-safe-args-gradle-plugin = { module = "androidx.navigation:navigation-safe-args-gradle-plugin", version.ref = "androidx-navigation" }