invalidate method
void
invalidate()
The next query rebuilds the cache. The document's changes stream
delivers only after the task that made a change, so whatever reads
the cache in the task of an edit calls this first: it must never read
an input the document no longer has. The Room tool calls it at its
click and again right after its execute; the Separator tool at its
second click, before the trim, and again right after its execute;
the separator grips at release, before they trim, since they never
execute (the select tool executes the command they return).
Implementation
void invalidate() {
_stale = true;
_generation++;
}