Last paragraph.With the mention of a "sprinkling of holy water", I'd have thought there'd be a similar consumption of the "powdered ruby". Is there any reason to think this wouldn't be the case?
"...If you cast forbiddance every day for 30 days in the same location, the spell lasts until it is dispelled, and the material components are consumed on the last casting."
The parenthetical with the material components also doesn't say consumed. Compare to Raise Dead:
"* - (a diamond worth at least 500 gp, which the spell consumes)"
A few other spells use a "sprinkling" of holy water but have no listed material cost. I believe a Jeremy Crawford tweet said a sprinkling is a trivial amount so small that it has no effective cost (i.e. how many drops are in a pint?) I think there's some bad math there but its magic god-water so who knows, maybe it evaporates and goes back in the bottle.