* EXECUTE and FOUND - this is incompatible change, extra check can be used (test on unset variable). I see solution in leaving FOUND variable and introduction of some new without this issue - ROW_COUNT maybe (this is another possible incompatible change, but with higher benefit - maybe we can introduce some aliasing, PRAGMA clause, default PRAGMAs, ..).
I checked current implementation of FOUND variable. If we introduce new auto variable ROW_COUNT - exactly like FOUND, then it doesn't introduce any compatibility break.
ROW_COUNT .. shortcut for GET DIAGNOSTICS row_count = ROW_COUNT.