Terminal readout and ownership

Spectators may be returned or consumed by terminal $\mathrm{Enter}$. The partial trace in eq:spectatorresult describes an observation interface, not a term-level discard rule.

Nonselective terminal measurement of an entangled spectator preserves the original reduction. Conditional reductions need not be preserved. For a Bell pair, conditioning on the spectator's computational-basis outcome prepares the corresponding pure state on the original factor. Later geometry using that outcome is a different comparison.