After AUTH1 parks StepUpSK in SessionContext, the reader issues SELECT
to the Step-Up AID per spec §10.2. StepUpApplet.select() now picks up
the parked SK, derives StepUpSKDevice / StepUpSKReader via the
§8.4.3 HKDF (already implemented in AliroCrypto.deriveStepUpSessionKeys),
and stages both in transient CLEAR_ON_DESELECT fields for the ENVELOPE
(M1C.1) and EXCHANGE (M1B.1) handlers.
Introduces CryptoSingletons -- a lazy package-private holder for the
single AliroCrypto instance shared between AliroApplet and StepUpApplet.
Saves ~352 B of transient (kdfWorkbuf + hkdfPrevT + expandScratch)
versus a per-applet duplicate. Java Card forbids new in <clinit> so
the singleton uses lazy null-check init. Opt 1 prelude per
docs/plans/2026-06-11-step-up-implementation-v2.md.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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