A key-store lookup that threw (shared SQL Server unreachable, SQLite I/O
fault) escaped VerifyAsync despite the "only exception path is cancellation"
contract, surfacing as an unaudited 500 / gRPC Unknown. ApiKeyFailure gains
StoreUnavailable (appended; numeric values unchanged) and the lookup maps any
non-cancellation exception to it. Unit theory and an offline refused-port
SqlServerApiKeyStore test fail pre-fix.
(scadaproj#46)
Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
Joseph Doherty