Persistent boolean flag for the cached IssuerAuth verify result. Field
sits beside accessDocumentFinalized in writeTo/readFrom (FIELD_VERSION
bumped 1->2 -- schema change requires re-personalize). reset() clears.
Test pins the serialize/deserialize round-trip via the existing
RecordingSink/ReplaySource helpers.
Foundation for M2A.2 (CoseVerifier) and M2A.3 (verify-at-finalize wiring).
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