`tns migrate` clears the platforms and next build fails if a custom android runtime was used

If tns migrate was ran on an app with a custom android runtime (tns platform add android --frameworkPath /test/runtime.tgz), next build would fail. This is because the platforms/android folder is deleted and the version of the tns-android package was previously set in the package.json to the literal next version of the runtime. This runtime, of course, couldn't be found in npm and thus the build fails. Couldn't runtimes added with --frameworkPath be handled differently and in some way marked as such in the package.json? Also, couldn't a simple gradlew clean do the dirty work instead of deleting the whole platforms folder?

Start by tracing the tns migrate entry point and its handling of --frameworkPath, then inspect how package.json records the tns-android version and how platforms/android is removed. Compare that behavior with the mentioned gradlew clean option. Done means migrating an app with a custom runtime preserves a usable runtime reference and the next build succeeds.