EDIT. 2022.07.20
I found a simple partial solution by myself. “Do not put spy point on a predicate which has shift/1 in the body.” It might not be best one, but enough to encourage me to go to debugging.
IMHO. I take shift as throw, and reset as catch, but the thrown ball is always prolog goals in my case, which SWI-Prolog does not assume. If SWI-Prolog assumes goal ball as default, shift becomes a generalized phrase in DCG, and reset
gets more hidden from the user. I am writing this MHO remembering some well-known influencer words something like this: “While Haskell has monad, Prolog has DCG.”
END of EDIT
I use reset/shift as if it were the familiar DCG phrase for hiding information. It works almost as well as I expected, which is comfortable and I would like to extend my use of reset/shift in the future. However, there is one uncomfortable thing on reset/shift. There seems no way to skip shift/reset calls, which causes boring time to watch the display without any useful information. Roughly 99 percent of debugging Q/A interfaces related to reset/shift could be suppressed. In other words, it is enough for me to put spy points only on the user predicate calls other than reset/shift. Is there a way to tell swipl to ask to skip shift/skip ?