There's a tidy framework going around for idle game economy design.
Three sinks — Progression, Engagement, Prestige — and for each one, a row telling you what it absorbs: permanent upgrades, refills and boosts, cosmetic items.
Good starting map. But "absorbs" is doing something sneaky, and if you don't catch it you'll mis-tune every economy you touch.
A sink, by definition, destroys a resource. It's the opposite of a source, which mints resources into the economy. So when a framework says a sink "absorbs permanent upgrades," it's pointing at the wrong end of the pipe. Upgrades aren't destroyed — they're handed back to you. They're the output.
The thing that actually disappears — the thing the sink eats — is whatever you paid to get them.
