When a config file is deleted, the event handler sets file=null but
then force-unwraps it with file!! in the when block, crashing the
FileObserver thread. All subsequent config change notifications are
silently lost.
Replace force-unwrap with safe call, log a warning on deletion.
When the Java interceptor process dies, callback->transact() returns
DEAD_OBJECT but the code fell through to the real keystore, exposing
genuine TEE state to requesting apps.
Add pingBinder() liveness check on pre-transact failure. If the
interceptor is confirmed dead, return DEAD_OBJECT to the caller
instead of forwarding to real hardware. Apps see a transient service
error rather than the actual device attestation state.
