Never throws. An internal context this version does not model — a newer
native SDK's event, or one whose shape changed — round-trips unchanged
through OpaqueInternalContext instead. Throwing here would cost the
whole event: the beforeSend handler drops any event it cannot parse,
so an unrecognised internal context would silently delete telemetry that
apps without a beforeSend deliver normally.
Accepts anything the SDK may send — including a non-map value, which the
caller's cast used to throw on, dropping the event before this ran.