docs/RUST.md: the ABI-cache half of the build-apk.sh box is done (4f6ec3a)

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/RUST.md

@@ -725,9 +725,19 @@ closes it.
   `log_upload`, `POST /client-log` and the `AI_APP_LOG_*` baking went out
   whole rather than being rewired first -- done the same day, "Phone
   logging" above. `build.rs` had nothing left to do and is gone with them.
-- [ ] `iris/android-app/build-apk.sh`: clear Gradle's merged-native-libs
-  cache when the ABI changes (the x86_64 trap), and make the debug bench
-  APK installable (648 MB) -- RUST.md's logging section names both.
+- [~] `iris/android-app/build-apk.sh`. **First half done 2026-09-08**
+  (4f6ec3a): the script now removes `merged_native_libs`,
+  `stripped_native_libs` and `merged_jni_libs` alongside
+  `app/src/main/jniLibs`, since `mergeReleaseNativeLibs` is up to date
+  against its cached inputs and `rm -rf jniLibs` does not reach them.
+  Scoped to those three rather than all of `app/build`, so an ABI change
+  costs the native merge and not the whole Gradle build. Verified on the
+  case that produced it -- an x86_64 lib left in the checkout from
+  emulator work, then `./build-apk.sh release --abi arm64-v8a`, whose
+  APK's only `.so` is `lib/arm64-v8a/libmain.so`. **Still open**: the
+  debug bench APK is 648 MB and will not install
+  (`INSTALL_PARSE_FAILED_NOT_APK`), because the debug `libmain.so` is
+  325 MB; use `release` on the emulator until that is fixed.
 - [ ] Input-event and timing instrumentation into the log ring, copied
   by the report button. After the logging route lands (same ring).
 - [x] **Catch-a-fling (done 2026-09-07, b87f5a5; verified and ticked