Rust JNI

No compiler checks both sides of the JNI boundary. A wrong method name, an unguarded panic, an unattached thread, or a leaked local reference fails at run time on the device. Only a call from the JVM proves a binding; see Verify.

Pin the jni crate version

The jni API changed at 0.22. Code for 0.21 does not compile on 0.22. Read the locked version before you copy any snippet:

cargo tree --locked --target all -i jni --depth 0