The bank, the pool, and the rake.

Every credit to the pool is an atomic SQL + on the game’s prize_pool column — never an app-side read-modify-write, so two concurrent credits cannot lose an update. A Golden Room’s paid guess is two-sided: the keys fee is debited and the pool is funded by fee × 10 diamonds, in the same transaction.

defp charge_guess_golden(player, fee, ref) do
  Repo.transaction(fn ->
    case lock(player) do
      nil -> Repo.rollback(:no_player)
      p ->
        if p.keys < fee do
          Repo.rollback(:insufficient)
        else
          update!(p, %{keys: p.keys - fee})              # the keys debit
          txn!(player, :keys, -fee, "guess", ref)
          inc_pool!(ref, fee * Economy.diamonds_per_key()) # the pool +, fee×10
          p.keys - fee
        end
    end
  end)
end

defp inc_pool!(game, diamonds) do
  {1, _} = Repo.update_all(from(g in Game, where: g.id == ^game), inc: [prize_pool: diamonds])
end

The golden-economy story pins it: a golden guess with a fee of 1 key raises the pool by fee × 10 = 10 diamonds and the member’s keys fall by the fee — every guess is all-pay, and every guess funds the prize.

Economy.entry_fee_split/5 is pure, and it partitions each buy-in by the paid member’s ordinal into three bands. Select a band to see how much of the fee funds the pool versus stays platform revenue — the numbers are the golden-economy story’s (virtual_deposit 1000, threshold 2, first_movers 1, revenue 50%, fee 8 keys).

def entry_fee_split(ordinal, start_threshold, first_movers, revenue_pct, entry_fee_keys)
    when ordinal > start_threshold and ordinal <= start_threshold + first_movers do
  pool_keys = div(entry_fee_keys * (100 - revenue_pct), 100)
  pool_keys * @diamonds_per_key
end

def entry_fee_split(_ordinal, _start_threshold, _first_movers, _revenue_pct, _entry_fee_keys), do: 0

The keys portion is floored before the ×10 keys-to-diamonds conversion, so the pool conserves to whole diamonds. The house cut and the pool share derive from the one floor, so they partition the fee exactly with no residue.

The house’s own signed books — the RVL revenue ledger that records every platform movement, and cash-out (the forward cm.8) — are C6. This dive is the pool: where its diamonds come from, and how the fee is split.