DERIVE the console-wide RecallSafeMask from the per-channel rows.
This is the whole of "the console-wide view of recall-safe": a fold over the rows, computed
where a recall needs it and discarded again. Nothing holds the result — a mask that were held
would be a second owner of every channel's decision, and it could only ever be as fresh as the
last door that remembered to update it.
DERIVE the console-wide RecallSafeMask from the per-channel rows.
This is the whole of "the console-wide view of recall-safe": a fold over the rows, computed where a recall needs it and discarded again. Nothing holds the result — a mask that were held would be a second owner of every channel's decision, and it could only ever be as fresh as the last door that remembered to update it.