Step 10H.2: each board contract pays its own market rate

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

memory-bank/progress.md

@@ -218,3 +218,4 @@ Spec: `memory-bank/change-requests/CR-007-cargo-goods.md` (supplied as "CR-005 /
 
 Spec: `memory-bank/change-requests/CR-008-fresh-boards.md`. New decisions recorded as plan §0.5.60–0.5.62.
 - [x] **Step 10H.1 — Content: pay variance and new goods.** Config `contractPayVariance` 0.15. Five Standard goods (decision 0.5.61): Water Recyclers, Spare Parts (Priority-eligible) and Lunar Base Supplies Earth → Moon; Crew Personal Effects and Recycled Alloys Moon → Earth (locations' goods lists update from the catalog). Earth → Moon now has 6 Standard goods, Moon → Earth 4. All existing tests still pass (tutorial masses unchanged: goods on both routes still hold 5/12/20 t). Test: `goods.test.ts` (route variety, variance is a fraction).
+- [x] **Step 10H.2 — Sim: per-contract pay rate.** `PayoutInput.marketRate` (default 1) multiplies the payout; `payRate(rng, content)` draws 1 ± `contractPayVariance` uniformly as the last draw of every board contract (fit and normal); `buildContract` takes `payRate` (tutorial boards pass none, so tutorial payouts are unchanged). Tests: `pay-rate.test.ts` (payout scales with the rate; 1,000 Earth boards: rates within ±15 %, mean within 1 ± 0.01; the same good, mass and route now pays different amounts); the tutorial and CR-007 class-mix tests still pass.

packages/sim/src/board.ts

@@ -252,6 +252,11 @@ function rollPriority(
   return { priority: true, deliveryWindowGameHours: window };
 }
 
+/** A board contract's market rate: uniform within ± `contractPayVariance` of 1 (decision 0.5.60). */
+export function payRate(rng: Rng, content: SimContent): number {
+  return 1 + content.config.contractPayVariance * (2 * rng.next() - 1);
+}
+
 export function cargoClassOf(good: Good, content: SimContent): CargoType {
   const cargoType = content.cargoTypes.find((c) => c.id === good.cargoClassId);
   if (!cargoType) throw new Error(`Unknown cargo class ${good.cargoClassId}`);
@@ -284,6 +289,8 @@ export function buildContract(
     shipper: string;
     priority: boolean;
     deliveryWindowGameHours: number | null;
+    /** Market rate (decision 0.5.60); 1 when absent, as on the tutorial board. */
+    payRate?: number;
   },
   content: SimContent,
 ): Contract {
@@ -311,6 +318,7 @@ export function buildContract(
         distanceMillionKm: distance,
         firstContact: args.firstContact,
         priority: args.priority,
+        marketRate: args.payRate ?? 1,
       },
       config,
     ),
@@ -408,6 +416,7 @@ export function generateContractBoard(input: BoardInput, content: SimContent): C
           periodIndex,
           ...rollPriority(rng, { ...job, origin, offeredAt, model }, content),
           shipper: rng.pick(origin.shippers),
+          payRate: payRate(rng, content),
         },
         content,
       );
@@ -438,6 +447,7 @@ export function generateContractBoard(input: BoardInput, content: SimContent): C
         periodIndex,
         ...rollPriority(rng, { good, origin, destination, massTonnes, offeredAt }, content),
         shipper: rng.pick(origin.shippers),
+        payRate: payRate(rng, content),
       },
       content,
     );

packages/sim/src/contract.ts

@@ -44,12 +44,14 @@ export interface PayoutInput {
   distanceMillionKm: number;
   firstContact: boolean;
   priority: boolean;
+  /** This contract's market rate around 1 (decision 0.5.60); 1 when absent. */
+  marketRate?: number;
 }
 
 /**
  * Payout in whole credits: class base pay per tonne per million km × the good's
  * pay multiplier × tierMultiplier^tier × mass × distance, × the first-contact
- * multiplier and the Priority bonus when flagged (CR-007).
+ * multiplier and the Priority bonus when flagged (CR-007), × its market rate (CR-008).
  */
 export function contractPayout(input: PayoutInput, config: GameConfig): number {
   const { cargoType, payMultiplier, tier, massTonnes, distanceMillionKm, firstContact } = input;
@@ -60,6 +62,7 @@ export function contractPayout(input: PayoutInput, config: GameConfig): number {
     massTonnes *
     distanceMillionKm *
     (firstContact ? config.firstContactPayoutMultiplier : 1) *
-    (input.priority ? config.priorityPayoutMultiplier : 1);
+    (input.priority ? config.priorityPayoutMultiplier : 1) *
+    (input.marketRate ?? 1);
   return Math.round(pay);
 }

packages/sim/test/pay-rate.test.ts

@@ -0,0 +1,82 @@
+import { content } from "@deadhead/content";
+import { describe, expect, it } from "vitest";
+import {
+  contractPayout,
+  generateContractBoard,
+  realToGame,
+  routeDistance,
+  type Contract,
+} from "../src/index";
+
+const { config } = content;
+const v = config.contractPayVariance;
+const all = new Set(content.locations.map((l) => l.id));
+
+/** The contract's payout without its market rate, from the same inputs. */
+function basePayout(c: Contract): number {
+  const good = content.good(c.goodId)!;
+  return contractPayout(
+    {
+      cargoType: content.cargoType(c.cargoTypeId)!,
+      payMultiplier: good.payMultiplier,
+      tier: c.tier,
+      massTonnes: c.massTonnes,
+      distanceMillionKm: routeDistance(
+        content.location(c.originId)!,
+        content.location(c.destinationId)!,
+        realToGame(c.offeredAt, config),
+      ),
+      firstContact: c.firstContact,
+      priority: c.priority,
+    },
+    config,
+  );
+}
+
+const contracts = Array.from({ length: 1000 }, (_, p) =>
+  generateContractBoard(
+    { location: content.location("earth")!, discoveredIds: all, periodIndex: p, worldSeed: 99 },
+    content,
+  ),
+).flat();
+
+describe("market rate (CR-008)", () => {
+  it("scales a payout by its rate", () => {
+    const input = {
+      cargoType: content.cargoType("standard")!,
+      payMultiplier: 1,
+      tier: 0,
+      massTonnes: 10,
+      distanceMillionKm: 100,
+      firstContact: false,
+      priority: false,
+    };
+    expect(contractPayout({ ...input, marketRate: 1.1 }, config)).toBe(
+      Math.round(contractPayout(input, config) * 1.1),
+    );
+  });
+
+  it("keeps every board contract's rate within ±variance, averaging 1", () => {
+    // Ignore tiny payouts, where rounding to whole credits blurs the rate.
+    const rates = contracts
+      .filter((c) => basePayout(c) >= 200)
+      .map((c) => c.payout / basePayout(c));
+    expect(rates.length).toBeGreaterThan(1000);
+    for (const rate of rates) {
+      expect(rate).toBeGreaterThanOrEqual(1 - v - 0.005);
+      expect(rate).toBeLessThanOrEqual(1 + v + 0.005);
+    }
+    const mean = rates.reduce((a, b) => a + b, 0) / rates.length;
+    expect(Math.abs(mean - 1)).toBeLessThanOrEqual(0.01);
+  });
+
+  it("no longer pays the identical amount for the same good, mass and route", () => {
+    const seen = new Map<string, Set<number>>();
+    for (const c of contracts) {
+      const key = `${c.goodId}|${c.massTonnes}|${c.destinationId}|${c.priority}|${c.firstContact}`;
+      seen.set(key, (seen.get(key) ?? new Set()).add(c.payout));
+    }
+    const repeated = [...seen.values()].filter((payouts) => payouts.size > 1);
+    expect(repeated.length).toBeGreaterThan(50);
+  });
+});