Prim.rts_heap_size() is erroneously zero

Debug.print(debug_show(Prim.rts_heap_size())); prints zero several times, despite I do add data to the canister.

It happens on

$(shell vessel bin)/moc -r $(shell vessel sources) -wasi-system-api test/*

Why does it print zero and how to obtain the real actor’s heap size?

Prim.rts_heap_size is probably not supported in the wasi-system-api. It needs dfx.