The RSA capability probe cached any first-call failure for the process
lifetime via by-lazy plus a catch-all false, so a transient keystore
hiccup could freeze the device into forging an attestation the real TEE
could serve, silently re-creating the issue #37 regression with no
self-heal.
Memoize only a definitive verdict: a successful probe, or a permanent
KeyStoreException per the framework's own isTransientFailure(). Transient
and non-keystore failures fail open, reporting the device attestable so
dispatch PATCHes the genuine chain, and re-probe on the next read. An
AtomicBoolean guard keeps at most one probe in flight with no lock held
across the keygen. Delete the probe key best-effort in finally.
Refs #37