feat: More bonus (exponential) and method to list icons needed

tests/engine.test.js

@@ -9,6 +9,7 @@ import {
   click,
   derive,
   generatorQuote,
+  materialPurchase,
   setPrice,
   simulateOffline,
   upgradeVisible,
@@ -311,3 +312,38 @@ test('state survives a serialize / sanitize round trip', () => {
   assert.equal(back.marketing, 3);
 });
 
+
+test('a partial lot can always be bought: material is never out of reach', () => {
+  const s = fresh();
+  s.upgrades = ['stack_1', 'stack_2', 'stack_3', 'stack_4', 'stack_5'];
+  s.endless = { e_stack: 30 }; // a lot far larger than any funds
+  s.generators.gen1 = 5;
+  s.material = 0;
+  s.funds = 50;
+  const d = derive(s, ctx);
+  assert.ok(d.batchCost > 1e6, 'the whole lot is out of reach');
+  const purchase = materialPurchase(s, d);
+  assert.equal(purchase.cost, 50, 'spends what it can');
+  assert.ok(Math.abs(purchase.amount / d.batchSize - 50 / d.batchCost) < 1e-12, 'proportional to the lot price');
+  assert.ok(buyMaterial(s, ctx));
+  assert.equal(s.funds, 0);
+  assert.ok(s.material > 0);
+  assert.equal(buyMaterial(s, ctx), false, 'nothing left to spend');
+});
+
+test('a whole lot is bought when affordable', () => {
+  const s = fresh();
+  s.funds = 1e6;
+  const d = derive(s, ctx);
+  assert.deepEqual(materialPurchase(s, d), { amount: d.batchSize, cost: d.batchCost });
+});
+
+test('auto-buy still restocks when the lot is out of reach (urgent partial buy)', () => {
+  const s = fresh();
+  s.upgrades = ['auto_buy'];
+  s.endless = { e_stack: 30 };
+  s.funds = 100;
+  s.material = 0;
+  advance(s, ctx, 0.1, () => 0.5);
+  assert.ok(s.material > 0);
+});