generateSecret takes a KeySpec; passing a JObject made the bridge emit a signature no method matches, and the call failed at runtime. Swallowed as 'unavailable', which hid my own mistake for a full test round - the failure now carries its exception message.
Measured on device: the Pascal PBKDF2 takes 6651 ms, unusable per unlock. AES-GCM through JNI works, plaintext and hash match the vector, so the container format is validated end to end.
The Pascal loop takes 1736 ms on a desktop CPU, so several seconds on a phone - too slow for every unlock. SecretKeyFactory is native and roughly an order of magnitude faster, but PBEKeySpec takes a char[] and the provider picks the encoding, which was the reason for avoiding it.
The non-ASCII vector settles it on a real device: same key means the provider uses UTF-8 and we adopt it; a different key means the Pascal implementation stays. DecryptContainer keeps using the Pascal one until that measurement says otherwise.
r-zakarya