Definition. Online measurable feedback [ftip-003Z]
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    Let \(\mathcal F_t\) be the sigma-algebra generated by the public history \(\mathsf H_t\) available through decision time \(t\). A feedback variable \(Z_t\) is online measurable at time \(t\) when it is \(\mathcal F_t\)-measurable and is delivered before the protocol chooses its next action.

    A label computed only after observing a later action or terminal outcome is not online measurable at the earlier time, even if it is subsequently attached to that earlier prefix in the training data.