Quantum memory for questions revealed after an early answer

An observer must answer a Boolean question during one-pass access to a quantum source and preserve evidence for a question revealed later. This preprint gives two explicitly specified source families with unlimited classical memory and a retained quantum-dimension cap at every contact boundary. For cycle witnesses, the exact worst-question frontier is V_d(k) = 1 - [1 - min{1, sqrt((d-1)/k)}] / 2^(k+ceil(log2 k)). Perfect answering needs dimension 2 for a question known initially and k+1 when it is revealed after the early deadline. A complete sequential instrument matches the all-strategy bound. Fixed positive early error permits constant dimension for cycle witnesses, whereas complete witnesses with inaccessible context force d^2-1 >= k(1-2 epsilon) when every later answer is exact. The 13-page manuscript includes proofs, source preparation, a repeated clock-controlled interaction, deadline controls and limitations. The accompanying archive contains LaTeX source, analytic notes, verification code and supplied/fresh execution records. Finite construction checks pass; novelty and external specialist review remain pending. Positive-error optimality, robustness to later error and nonvanishing unconditional success gaps are not established. Research preprint, not peer reviewed.