The materialization request. git-objects pairs with mode commit-pair
and index with mode index; the pairing law is checked against the
evaluation request by the consumer, since each request parses alone.
One supplied external control: the exact embedded JSON value, the
independently acquired expected semantic digest, and the external trust
source that authorized it.
Every request stream is one complete bounded byte capture from byte zero
through EOF; its diagnostic digest exists exactly when EOF was obtained
within this cap.