diff --git a/iris/android-app/build-apk.sh b/iris/android-app/build-apk.sh
index 19f94e0..7d4b8f2 100755
--- a/iris/android-app/build-apk.sh
+++ b/iris/android-app/build-apk.sh
@@ -57,6 +57,18 @@ export ANDROID_NDK_HOME="$NDK_DIR"
 # finds -- a debug x86_64 emulator build left behind made an arm64 "release"
 # 339 MB on 2026-09-06.
 rm -rf app/src/main/jniLibs
+# ...and Gradle's own copy of them, which `rm -rf jniLibs` does not reach.
+# `mergeReleaseNativeLibs` is *up to date* against its cached inputs, so a
+# build that switches ABI packages the previous ABI: an `--abi x86_64`
+# release APK containing `lib/arm64-v8a/libmain.so` installed fine and
+# aborted at startup with `Could not get adapter!: NotFound {
+# active_backends: VULKAN }` under libndk_translation -- which reads
+# exactly like the phone's own Vulkan problem and is nothing of the kind.
+# Scoped to the merge task's directory rather than all of `app/build`, so
+# an ABI change costs the native merge and not the whole Gradle build.
+rm -rf app/build/intermediates/merged_native_libs \
+       app/build/intermediates/stripped_native_libs \
+       app/build/intermediates/merged_jni_libs
 echo "build-apk.sh: cargo ndk -t $ABI build ${BUILD_TYPE:+(${BUILD_TYPE})} --features \"$FEATURES\""
 if [ "$BUILD_TYPE" = "release" ]; then
     cargo ndk -t "$ABI" -P 29 -o app/src/main/jniLibs/ build --release --features "$FEATURES"