Assumption: Atomic single-pass delivery

For a declared horizon, packets arrive once, in order. Each packet atomically occupies its entire declared binary width.

A passive supplier may buffer undelivered packets but may not measure, demultiplex, select, or decode them. The observer may pause delivery but may not revisit consumed packets, return intermediate quantum data to the supplier, use uncounted storage, share auxiliary entanglement, or export quantum output before consuming every horizon packet.

Classical memory is unrestricted. Every laboratory qubit is destructively measured or returned as the final output.