fixup! fix: document contract; refactor for clarity; use defensive pa…

…tterns

contract/src/offer-up.contract.js

@@ -13,7 +13,7 @@
 
 import { Far } from '@endo/far';
 import { M, getCopyBagEntries } from '@endo/patterns';
-import { AmountMath, AssetKind } from '@agoric/ertp/src/amountMath.js';
+import { AssetKind } from '@agoric/ertp/src/amountMath.js';
 import { AmountShape } from '@agoric/ertp/src/typeGuards.js';
 import { atomicRearrange } from '@agoric/zoe/src/contractSupport/atomicTransfer.js';
 import '@agoric/zoe/exported.js';
@@ -85,25 +85,22 @@ export const start = async zcf => {
   /**
    * a pattern to constrain proposals given to {@link tradeHandler}
    *
-   * The `Price` amount must use the brand from the `price` term.
+   * The `Price` amount must be >= `tradePrice` term.
    * The `Items` amount must use the `Item` brand and a bag value.
    */
   const proposalShape = harden({
-    give: { Price: { brand: tradePrice.brand, value: M.any() } },
+    give: { Price: M.gte(tradePrice) },
     want: { Items: { brand: itemBrand, value: M.bag() } },
     exit: M.any(),
   });
 
   /** a seat for allocating proceeds of sales */
   const proceeds = zcf.makeEmptySeatKit().zcfSeat;
 
-  /** @param {ZCFSeat} buyerSeat */
+  /** @type {OfferHandler} */
   const tradeHandler = buyerSeat => {
     // give and want are guaranteed by Zoe to match proposalShape
-    const { give, want } = buyerSeat.getProposal();
-
-    AmountMath.isGTE(give.Price, tradePrice) ||
-      Fail`${q(give.Price)} below required ${q(tradePrice)}}`;
+    const { want } = buyerSeat.getProposal();
 
     sum(bagCounts(want.Items.value)) <= maxItems ||
       Fail`max ${q(maxItems)} items allowed: ${q(want.Items)}`;