Step 15.4: sim: tank, burn, and refuel

Ships carry fuel: a leg burns from the tank at departure (no credits),
dispatch needs the fuel on board (not-enough-fuel), a leg's fuel cost
is fuel burned x the tank's average price, and Auto top-up refills on
landing with what the credits cover. The save gains tank fields (save
version 2, migration fills every tank). Market ships arrive full; the
deal's ships come with a quarter tank to keep the balance targets.

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

DECISIONS.md

@@ -1459,3 +1459,13 @@ Implementation decisions not spelled out in `memory-bank/implementation-plan.md`
 - **`checkRoute` and `rangeFrom` take the config**, since reach depends on the economic-distance curve; every caller already had the content bundle at hand.
 - **A trip is still charged at departure in this step**, now its leg fuel at the origin's price: the tank state arrives in 15.4. The balance targets all pass with it.
 - **The Market shows "Reach" (a full tank from Earth)** instead of "Range"; the upgrade screen shows the tank in fu. The fuel gauge and prices come in 15.7.
+
+## Step 15.4
+
+- **The engine's save fields and migration came in this step, not 15.6**: once the sim requires fuel on board, an engine without tanks can't dispatch anything. 15.6 keeps the refuel, policy and emergency fuel commands and their tests.
+- **Deal ships come with a quarter tank** (user decision; `config.deal.tankShare` 0.25). With full tanks the deal's Clipper flew to Mars at once and landed at minute 36; Market purchases happen when it lands, so the first one moved to 79 min, outside 45–75. A quarter tank leaves the Clipper earning locally until the player can fuel a Mars run, as before tanks: first purchase 64, discovery 49, loan 136, four ships 136 vs 136. Market ships still arrive full (CR-015 §3).
+- **Auto top-up spends the credits after this delivery's pay**: land, get paid, refuel. `affordableRefuel` never charges more than the credits on hand, rounding included.
+- **Costs are whole credits; fuel amounts are fractional fu**: a leg burns what the curve says, and the UI rounds fu for display.
+- **`credits` left the dispatch and deadhead proposals**: nothing in validation depends on cash any more, so keeping the field would have been misleading. `insufficient-credits` is replaced by `not-enough-fuel` in both failure lists.
+- **The migration fills tanks at the price where each ship sits** (the base price while in flight), so the first legs after an update cost what fuel there costs.
+- **The balance simulator models the player's "Refuel here first"**: before choosing work, an idle ship tops up where it is as far as credits go. The no-strand and soft-lock checks now ask "with a full tank" and "with the fuel on board plus what the credits buy" instead of "with any credits".

apps/web/e2e/12-4-offline-progress.e2e.ts

@@ -28,8 +28,11 @@ test.describe("end to end (Phase 12)", () => {
     const summary = (await state(later)).summaries.find((s) => s.dispatchId === dispatchId)!;
     await expect(logbook(later)).toContainText(`Delivered ${summary.massTonnes} t`);
     const after = await state(later);
-    // Credits went up by the delivery's net payout; the ship is at the destination.
+    // Credits went up by the delivery's net payout, less any Auto top-up on landing
-    expect(after.company.credits).toBe(before.company.credits + summary.credits);
+    // (CR-015); the ship is at the destination.
+    expect(after.company.credits).toBe(
+      before.company.credits + summary.credits - (summary.topUp?.cost ?? 0),
+    );
     expect(after.ships.find((s) => s.id === flight.shipId)!.locationId).toBe(flight.destinationId);
   });
 });

apps/web/e2e/12-5-discovery.e2e.ts

@@ -1,5 +1,7 @@
 import { expect, test } from "@playwright/test";
+import type { Dispatch } from "@deadhead/schema";
 import {
+  acknowledgeAll,
   addCredits,
   advanceTo,
   board,
@@ -7,6 +9,7 @@ import {
   logbook,
   nextMarsWindow,
   playToDeal,
+  run,
   serverNow,
   state,
   tryDispatch,
@@ -29,6 +32,19 @@ test.describe("end to end (Phase 12)", () => {
     }
     await addCredits(page, 100_000);
 
+    // The deal's Clipper comes with a quarter tank (CR-015): an Earth–Moon round
+    // trip on Auto top-up lands it back at Earth full.
+    for (const destinationId of ["moon", "earth"]) {
+      const { dispatch } = await run<{ dispatch: Dispatch }>(page, "createDispatch", {
+        kind: "reposition",
+        shipId: clipper.id,
+        pilotId: veteran.id,
+        destinationId,
+      });
+      await advanceTo(page, dispatch.arrivalAt);
+    }
+    await acknowledgeAll(page);
+
     // The board offers a first contact the Clipper can fly (decision 0.5.85).
     const offer = (await board(page, "earth")).contracts.find(
       (c) => c.firstContact && c.destinationId === "mars",

apps/web/src/game.ts

@@ -59,6 +59,7 @@ export function simShip(ship: Ship): ShipState {
     inFlight: ship.status === "in-flight",
     upgrades: ship.upgrades,
     inShopUntil: ship.inShopUntil,
+    tank: { fuelFu: ship.fuelFu, avgPrice: ship.fuelAvgPrice },
   };
 }
 

apps/web/src/screens/DispatchSheet.tsx

@@ -10,7 +10,7 @@ import {
   LONG_HAUL_SKILL_ID,
   needsRest,
   realToGame,
-  tripFuelCost,
+  tripFuel,
   tripGameHours,
   validateDispatch,
   wouldStrand,
@@ -58,7 +58,7 @@ export const INELIGIBLE_REASONS: Record<DispatchFailure, string> = {
   "cargo-skill-too-low": "Cargo skill too low",
   "long-haul-too-low": "Long Haul too low",
   "contract-expired": "Contract expired",
-  "insufficient-credits": "Not enough credits for fuel",
+  "not-enough-fuel": "Not enough fuel",
 };
 
 /** The no-strand rule in words (CR-012), for the dispatch sheet and deadhead picker. */
@@ -82,7 +82,8 @@ export function explainProblems(
   contract: Contract,
   model: ShipModel,
   pilot: Pilot,
-  fuelCost: number,
+  /** The leg's fuel and what the ship has on board, in fu (CR-015). */
+  fuel: { neededFu: number; onBoardFu: number },
   gameNow: number,
   now: number,
 ): string[] {
@@ -137,8 +138,10 @@ export function explainProblems(
     problems.push(`Needs Long Haul ${contract.requiredLongHaulLevel} (pilot has ${longHaul})`);
   }
   if (now >= contract.expiresAt) problems.push(INELIGIBLE_REASONS["contract-expired"]);
-  if (state.company.credits < fuelCost) {
+  if (fuel.onBoardFu < fuel.neededFu) {
-    problems.push(`Not enough credits for fuel (${formatCredits(fuelCost)})`);
+    problems.push(
+      `Not enough fuel (needs ${Math.ceil(fuel.neededFu)} fu, has ${Math.floor(fuel.onBoardFu)} fu)`,
+    );
   }
   return problems;
 }
@@ -192,12 +195,14 @@ export function pairOptions(state: PlayerState, contract: Contract, now: number)
         contract.destinationId,
         contract.massTonnes,
       );
-      const fuelCost = tripFuelCost(
+      const fuelFu = tripFuel(
         model,
         location(contract.originId),
         location(contract.destinationId),
         content.config,
       );
+      // The fuel used, at the tank's average price (decision 0.5.98).
+      const fuelCost = Math.round(fuelFu * ship.fuelAvgPrice);
       // Profit-share pay for a hired pilot; the avatar is exempt (CR-010).
       const pilotPay =
         pilot && !pilot.isAvatar ? pilotShare(contract.payout, fuelCost, content.config) : 0;
@@ -217,7 +222,6 @@ export function pairOptions(state: PlayerState, contract: Contract, now: number)
             },
             contract,
             tutorial: false,
-            credits: state.company.credits,
             now,
             discoveredIds: discoveredIdsOf(state),
           },
@@ -227,7 +231,15 @@ export function pairOptions(state: PlayerState, contract: Contract, now: number)
         if (check.ok) {
           problems = [];
         } else {
-          const all = explainProblems(state, contract, model, pilot, fuelCost, gameNow, now);
+          const all = explainProblems(
+            state,
+            contract,
+            model,
+            pilot,
+            { neededFu: fuelFu, onBoardFu: ship.fuelFu },
+            gameNow,
+            now,
+          );
           // In the shop (CR-009): first, with the time left.
           if (isInShop(ship, now))
             all.unshift(

apps/web/src/screens/Fleet.tsx

@@ -2,7 +2,7 @@ import { content } from "@deadhead/content";
 import type { Dispatch, Ship } from "@deadhead/schema";
 import {
   dispatchProgress,
-  tripFuelCost,
+  tripFuel,
   validateReposition,
   type RepositionFailure,
 } from "@deadhead/sim";
@@ -188,7 +188,7 @@ const DEADHEAD_REASONS: Partial<Record<RepositionFailure, string>> = {
   "cannot-land": "Can't land there",
   "out-of-range": "Out of range",
   "would-strand": "Would be stranded",
-  "insufficient-credits": "Not enough credits for fuel",
+  "not-enough-fuel": "Not enough fuel",
   "ship-in-shop": "Ship is in the shop",
   "pilot-resting": "Pilot is resting",
   "pilot-not-idle": "Pilot is flying",
@@ -226,7 +226,6 @@ export function DeadheadPicker({ ship, onClose }: { ship: Ship; onClose: () => v
           },
           destinationId: id,
           discoveredIds,
-          credits: state.company.credits,
           now,
         },
         content,
@@ -238,7 +237,10 @@ export function DeadheadPicker({ ship, onClose }: { ship: Ship; onClose: () => v
           : check.reason === "would-strand"
             ? strandedText(id)
             : (DEADHEAD_REASONS[check.reason] ?? check.reason),
-        fuelCost: tripFuelCost(model, location(origin), location(id), content.config),
+        // The fuel used, at the tank's average price (decision 0.5.98).
+        fuelCost: Math.round(
+          tripFuel(model, location(origin), location(id), content.config) * ship.fuelAvgPrice,
+        ),
         tripMs: tripRealMs(model, origin, id, 0),
       };
     });

apps/web/test/about.test.tsx

@@ -23,7 +23,7 @@ describe("about and debug info (Step 10K.10)", () => {
     expect(text).toContain("Build: test");
     // CR-014: the save, its format version and where it is stored; no player id.
     expect(text).toContain("Save: player-1");
-    expect(text).toContain("Save version: 1");
+    expect(text).toContain("Save version: 2");
     expect(text).toContain("Storage: unknown");
     expect(text).not.toContain("Player:");
     expect(text).toMatch(/Game time: \d{4}-\d{2}-\d{2}T/);

apps/web/test/away-goals.test.tsx

@@ -35,6 +35,7 @@ function returningPlayer(acknowledged: boolean): PlayerState {
             credits: 538,
             deadhead: false,
             fuelCost: 0,
+            topUp: null,
             goodId: "consumer-goods",
             massTonnes: 12,
             shipper: "Pacific Orbital Logistics",

apps/web/test/away-summary.test.tsx

@@ -27,6 +27,7 @@ const summaries: ResolutionSummary[] = [
     credits: 51_200,
     deadhead: false,
     fuelCost: 0,
+    topUp: null,
     goodId: "consumer-goods",
     massTonnes: 12,
     shipper: "Pacific Orbital Logistics",
@@ -48,6 +49,7 @@ const summaries: ResolutionSummary[] = [
     credits: 240,
     deadhead: false,
     fuelCost: 0,
+    topUp: null,
     goodId: "consumer-goods",
     massTonnes: 12,
     shipper: "Pacific Orbital Logistics",
@@ -90,6 +92,7 @@ describe("while you were away", () => {
       destinationId: "moon",
       deadhead: true,
       fuelCost: 230,
+      topUp: null,
       goodId: null,
       massTonnes: null,
       shipper: null,

apps/web/test/deal-modal.test.tsx

@@ -103,6 +103,7 @@ describe("the deal", () => {
           credits: 96,
           deadhead: false,
           fuelCost: 0,
+          topUp: null,
           goodId: "consumer-goods",
           massTonnes: 12,
           shipper: "Pacific Orbital Logistics",

apps/web/test/dev-tools.test.tsx

@@ -19,6 +19,7 @@ describe("developer tools in Settings (Step 10K.11)", () => {
       arrivalAt: now + 5 * 60_000,
       distanceMillionKm: 0.4,
       fuelCost: 0,
+      fuelBurnedFu: 0,
       expectedPayout: 0,
       seed: 1,
       status: "in-flight",

apps/web/test/dispatch-sheet.test.tsx

@@ -5,7 +5,7 @@ import {
   realToGame,
   routeDistance,
   travelTimeGameHours,
-  tripFuelCost,
+  tripFuel,
   pilotShare,
 } from "@deadhead/sim";
 import { screen, waitFor, within } from "@testing-library/react";
@@ -120,7 +120,8 @@ describe("dispatch sheet", () => {
       (travelTimeGameHours(model, routeDistance(earth, mars), marsJob.massTonnes, content.config) *
         MS_PER_HOUR) /
       content.config.timeCompression;
-    const fuel = tripFuelCost(model, earth, mars, content.config);
+    // The fixtures' tanks were filled at 16 cr/fu (CR-015).
+    const fuel = Math.round(tripFuel(model, earth, mars, content.config) * 16);
     const net = marsJob.payout - fuel - pilotShare(marsJob.payout, fuel, content.config);
 
     expect(within(freighter).getByRole("radio")).toBeEnabled();

apps/web/test/fixtures.ts

@@ -11,7 +11,10 @@ import { effectiveStats } from "@deadhead/sim";
 export function shipExtras(
   modelId: string,
   upgrades: Record<string, number> = {},
-): Pick<Ship, "upgrades" | "stats" | "inShopUntil" | "shop"> {
+): Pick<
+  Ship,
+  "upgrades" | "stats" | "inShopUntil" | "shop" | "fuelFu" | "fuelAvgPrice" | "refuelPolicy"
+> {
   const model = content.shipModel(modelId);
   if (!model) throw new Error(`Unknown ship model ${modelId}`);
   const s = effectiveStats(model, upgrades, content);
@@ -27,6 +30,10 @@ export function shipExtras(
     },
     inShopUntil: null,
     shop: null,
+    // A full tank bought at Earth (CR-015).
+    fuelFu: s.tankCapacityFu,
+    fuelAvgPrice: 16,
+    refuelPolicy: "auto",
   };
 }
 

apps/web/test/fleet.test.tsx

@@ -22,6 +22,7 @@ const flight: Dispatch = {
   arrivalAt: NOW + 180_000,
   distanceMillionKm: 0.39,
   fuelCost: 50,
+  fuelBurnedFu: 0,
   expectedPayout: 0,
   seed: 1,
   status: "in-flight",
@@ -149,7 +150,14 @@ describe("fleet screen", () => {
     const record = createRepositionRecord(
       {
         id: "r",
-        ship: { id: "s-idle", modelId: "courier", locationId: "moon", inFlight: false },
+        // The fixture's tank was filled at 16 cr/fu (CR-015).
+        ship: {
+          id: "s-idle",
+          modelId: "courier",
+          locationId: "moon",
+          inFlight: false,
+          tank: { fuelFu: 40, avgPrice: 16 },
+        },
         pilot: {
           id: "avatar",
           isAvatar: true,

apps/web/test/hq.test.tsx

@@ -32,6 +32,7 @@ const dispatch = (shipId: string, arrivalAt: number): Dispatch => ({
   arrivalAt,
   distanceMillionKm: 0.39,
   fuelCost: 50,
+  fuelBurnedFu: 0,
   expectedPayout: 0,
   seed: 1,
   status: "in-flight",
@@ -149,6 +150,7 @@ describe("loan on HQ", () => {
           credits: 538,
           deadhead: false,
           fuelCost: 0,
+          topUp: null,
           goodId: "consumer-goods",
           massTonnes: 12,
           shipper: "Pacific Orbital Logistics",

apps/web/test/map-art-loading.test.ts

@@ -20,6 +20,7 @@ const flight = (id: string, shipId: string, tutorial = false): Dispatch => ({
   arrivalAt: NOW + 60_000,
   distanceMillionKm: 0.4,
   fuelCost: 0,
+  fuelBurnedFu: 0,
   expectedPayout: 0,
   seed: 1,
   status: "in-flight",

apps/web/test/map-interactions.test.tsx

@@ -22,6 +22,7 @@ const flight: Dispatch = {
   arrivalAt: NOW + 5 * 60_000,
   distanceMillionKm: 100,
   fuelCost: 0,
+  fuelBurnedFu: 0,
   expectedPayout: 0,
   seed: 1,
   status: "in-flight",

apps/web/test/map-layout.test.ts

@@ -123,6 +123,7 @@ describe("bodies on screen (decisions 0.5.38, 0.5.39)", () => {
           arrivalAt: now + 60_000,
           distanceMillionKm: 0.4,
           fuelCost: 0,
+          fuelBurnedFu: 0,
           expectedPayout: 0,
           seed: 1,
           status: "in-flight",

apps/web/test/map-scene.test.ts

@@ -18,6 +18,7 @@ const flight: Dispatch = {
   arrivalAt: NOW + 3_600_000,
   distanceMillionKm: 150,
   fuelCost: 0,
+  fuelBurnedFu: 0,
   expectedPayout: 0,
   seed: 1,
   status: "in-flight",

apps/web/test/pilot-share.test.tsx

@@ -1,6 +1,6 @@
 import { content } from "@deadhead/content";
 import type { Contract, Pilot, ResolutionSummary, Ship } from "@deadhead/schema";
-import { pilotShare, tripFuelCost } from "@deadhead/sim";
+import { pilotShare, tripFuel } from "@deadhead/sim";
 import { screen, within } from "@testing-library/react";
 import userEvent from "@testing-library/user-event";
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
@@ -65,6 +65,7 @@ const summary: ResolutionSummary = {
   tutorial: false,
   deadhead: false,
   fuelCost: 150,
+  topUp: null,
   goodId: "consumer-goods",
   massTonnes: 10,
   shipper: "Pacific Orbital Logistics",
@@ -106,11 +107,14 @@ describe("pilot share in the client (Step 10J.6)", () => {
     );
     await userEvent.click(await screen.findByRole("button", { name: "Dispatch" }));
     const dialog = screen.getByRole("dialog");
-    const fuel = tripFuelCost(
+    // The fixtures' tanks were filled at 16 cr/fu (CR-015).
-      content.shipModel("courier")!,
+    const fuel = Math.round(
-      content.location("earth")!,
+      tripFuel(
-      content.location("moon")!,
+        content.shipModel("courier")!,
-      content.config,
+        content.location("earth")!,
+        content.location("moon")!,
+        content.config,
+      ) * 16,
     );
     const share = pilotShare(job.payout, fuel, content.config);
 

apps/web/test/player-state.test.tsx

@@ -20,6 +20,7 @@ function inFlight(arrivalAt: number): Dispatch {
     arrivalAt,
     distanceMillionKm: 0.39,
     fuelCost: 0,
+    fuelBurnedFu: 0,
     expectedPayout: 240,
     seed: 1,
     status: "in-flight",

apps/web/test/rest-summary-hq.test.tsx

@@ -36,6 +36,7 @@ const summary = (extra: Partial<ResolutionSummary>): ResolutionSummary => ({
   credits: 500,
   deadhead: false,
   fuelCost: 0,
+  topUp: null,
   goodId: "consumer-goods",
   massTonnes: 12,
   shipper: "Pacific Orbital Logistics",

apps/web/test/tutorial-board.test.tsx

@@ -144,6 +144,7 @@ describe("scripted delivery summary", () => {
                 credits: 461,
                 deadhead: false,
                 fuelCost: 0,
+                topUp: null,
                 goodId: "consumer-goods",
                 massTonnes: 12,
                 shipper: "Pacific Orbital Logistics",

memory-bank/architecture.md

@@ -7,7 +7,7 @@ Living reference for how the code is organised. Update it after any save format
 | Package | Role | Depends on |
 |---|---|---|
 | `packages/content` | Static game data (locations, ship models, cargo, skills, `GameConfig`) as Zod-validated TypeScript, plus the `content` bundle with id lookups. | zod |
-| `packages/sim` | Pure, deterministic game rules: clock, seeded RNG, positions, distances, travel, fuel, eligibility, contract boards, dispatch validation/records, flight progress, XP, resolution. No I/O, no `Date.now()`, no `Math.random()`. `balance/` holds the balance simulation (Step 12.1), outside `src/` and the coverage measure. Positions are fixed (CR-015): `locationPosition` reads the location's `position` from content. Fuel (`fuel.ts`, CR-015): `legFuel` = burn × economic distance(distance ÷ origin factor), `fullTankReach` (its inverse for a full tank), `fuelPriceAt`; `checkRoute(ship, from, to, config)` compares the distance with full-tank reach. | content |
+| `packages/sim` | Pure, deterministic game rules: clock, seeded RNG, positions, distances, travel, fuel, eligibility, contract boards, dispatch validation/records, flight progress, XP, resolution. No I/O, no `Date.now()`, no `Math.random()`. `balance/` holds the balance simulation (Step 12.1), outside `src/` and the coverage measure. Positions are fixed (CR-015): `locationPosition` reads the location's `position` from content. Fuel (`fuel.ts`, CR-015): `legFuel` = burn × economic distance(distance ÷ origin factor), `fullTankReach` (its inverse for a full tank), `fuelPriceAt`; `checkRoute(ship, from, to, config)` compares the distance with full-tank reach. Tanks (Step 15.4): `ShipState.tank` (`fuelFu`, `avgPrice`), `refuel`, `affordableRefuel`, `legFuelCost`; validation fails with `not-enough-fuel`; records carry `fuelBurnedFu` and `fuelCost` (burned × average price); `resolveDispatch` takes an optional `fuel` block and returns `topUp` (Auto top-up on landing). | content |
 | `packages/engine` | The game on the device (CR-014): commands over a save document, using storage, the clock and notifications only through injected interfaces. `notifications.ts`: the schedule is recomputed from the save after every saved change and replaces the platform's (`NotificationScheduler`: Capacitor on native, no-op on the web). `DeviceClock`: `max(device time + dev offset, last time seen)`, never backward. | content, schema, sim |
 | `packages/schema` | Zod schemas for every API request, response and error. Shared by the engine and the client. | sim (error codes), zod |
 | `apps/web` | React client; runs the engine on the device (CR-014). | content, engine, sim, schema |
@@ -76,7 +76,7 @@ The `routes` catalog is the list of engine commands (CR-014). Each entry has `re
 
 ## Save document (`packages/schema/src/save.ts`, CR-014)
 
-One document per company on the device, validated on every load and save: `saveVersion` (currently 1), `saveId`, `lastTimeSeen` (the clock never goes below it), `player` (world seed, tutorial state, deal accepted), `company` (name, credits, loan), `ships` (with `upgrades` as a level map and shop fields), `pilots`, `bays`, `discoveredLocations`, `contractBoards` (stored boards), `dispatches` (sim record, status, resolution, acknowledged), `acceptedContracts`, `claimedGoals`. It mirrors the old server's database tables without player ids; the stored contract, dispatch record and resolution are type-checked against the sim types. `migrateSave(raw)` steps an older save through `SAVE_MIGRATIONS` (`applyMigrations`) and validates it, returning a readable error instead of throwing.
+One document per company on the device, validated on every load and save: `saveVersion` (currently 2; 1 → 2 added fuel tanks, CR-015), `saveId`, `lastTimeSeen` (the clock never goes below it), `player` (world seed, tutorial state, deal accepted), `company` (name, credits, loan), `ships` (with `upgrades` as a level map, shop fields, and `fuelFu`, `fuelAvgPrice`, `refuelPolicy` since CR-015), `pilots`, `bays`, `discoveredLocations`, `contractBoards` (stored boards), `dispatches` (sim record, status, resolution, acknowledged), `acceptedContracts`, `claimedGoals`. It mirrors the old server's database tables without player ids; the stored contract, dispatch record and resolution are type-checked against the sim types. `migrateSave(raw)` steps an older save through `SAVE_MIGRATIONS` (`applyMigrations`) and validates it, returning a readable error instead of throwing.
 
 Commands (`packages/engine/src/game/`): `GameEngine.call(name, input)` runs the route catalog's endpoints on the save, with the same schemas and error codes (`CommandError`); `getPlayerState` with no save answers `unauthorized`. Every command resolves due arrivals first and prunes on save; saves are skipped when nothing changed. `stats` keeps lifetime delivery counts for goals, so seen trips older than `savedDispatchRetentionRealHours` can be pruned.
 

memory-bank/progress.md

@@ -373,7 +373,7 @@ Spec: `memory-bank/change-requests/CR-015-fixed-map-fuel-tanks.md` (received as
 - [x] **Step 15.1 — Content: fixed positions.** Locations lose `body` and gain `position` (`{ radiusMillionKm, angleDegrees }`): Earth 150/210°, Mars 228/270°, Ceres Station 414/285°, Jupiter Cloud Platform 778/300°; the Moon is Earth's position moved 0.384M km straight out (`offsetPosition`), recorded as `orbitParent: { locationId: "earth", offsetMillionKm: 0.384 }`. GameConfig's epoch keeps only a displayed start date (`gameStart`, was `ephemerisDate`; same value). `astronomy-engine` is removed from the sim and the lockfile. Because positions had to come from somewhere once it was gone, the sim's `locationPosition` already reads the fixed position (its game-time argument is ignored until 15.2), and the web map draws from it (`bodyPosition` is gone; the Moon is placed from `orbitParent`). Fixed distances broke CR-012's tuning, so ranges move into CR-015 §4's bands now: Clipper 198 → 250M km (it couldn't reach Mars at 201), Freighter 450 → 460, the Courier's fuel-tank override 450 % → 1,400 % per level (5 → 75 → 145 → 215: Mars from Earth only at level 3). The balance re-check then put the first Market purchase at 86.7 min (quantized by the Clipper's first Mars landing), so the Lighter's price drops 42,400 → 36,000 (first purchase 53.3, four ships 115 vs 130 min, loan 135 min). Tests: `packages/content/test/fixed-map.test.ts` (every location positioned; the Moon defined as an offset from Earth; child bodies match their parent plus offset; the six §2 distances within 2 % and symmetric; no `astronomy-engine` in the lockfile). Date-sampled tests became yes/no: `reach-table.test.ts` is now CR-015 §4, one test per cell; `courier-mars`, `eligibility`, the distance test ("varies" replaced by "the same at every time"), the upgrade-cap value; the engine's would-strand test and the web stranding test use a maxed-tank Freighter at the Moon going to Jupiter with Mars and Ceres undiscovered (no base ship can strand on the fixed map); the Market test for "Other dates" is removed (the wording goes in 15.8).
 - [x] **Step 15.2 — Sim: static positions and distances.** No time arguments left where a time only fed a position: `locationPosition(location)`, `routeDistance(from, to)`, `checkRoute(ship, from, to)`, `tripFuelCost(model, origin, destination, config)`, `contractTripGameHours(model, contract, content)`, `priorityWindow(origin, destination, mass, content)`, and `wouldStrand(model, destination, discoveredIds, content)` (it had taken cargo mass and departure only to find where planets would be on arrival). `dispatchPosition` runs along the fixed line. Board generation, records and validation no longer convert real to game time for distance. GameConfig's `noStrandMarginGameHours` is gone (nothing moves in 48 game hours now). Web: `distanceAt`, `tripRealMs`, `locationMapPoint`, `reachersByOrigin`, `tooSlowForAll` and `shipReach` lose their time argument; `shipReach` checks each leg once instead of sampling 16 game years (its `otherDates` is always empty and goes with its wording in 15.8). Callers were updated with a small argument-dropping codemod, then the unused time variables removed. Tests: `distance.test.ts` per the CR (Earth→Moon under 1M km, symmetric, same value for the same inputs; the "varies" test is gone), `positions.test.ts` ("never moves"), new `static-routes.test.ts` (an Earth → Ceres contract pays the same in any board period; a Freighter's trip takes the same time, distance and fuel whenever it departs); `no-strand.test.ts` now checks that no base ship is ever blocked on a leg it can fly; `range-from` and `upgrade-caps` lose their date loops.
 - [x] **Step 15.3 — Content: fuel.** ShipModel: `fuelRangeMillionKm` and `fuelCostPerMillionKm` replaced by `tankCapacityFu` and `burnFuPerMillionKm` (Courier 40/20, Lighter 110/35, Clipper 1,170/45, Freighter 1,540/40, Bulk Hauler 5,900/80, loaner 40/20). Location: `launchCostMultiplier` replaced by `fuelPrice` (× base: Jupiter 0.6, Ceres 0.9, Moon 1.1, Mars 1.4, Earth 1.6) and `sellsFuel` (all true). GameConfig: `baseFuelPricePerFu` 10, `emergencyFuelMultiplier` 2.5. Extended Fuel Tanks raises `tankCapacityFu`: 11 %/level by default, Courier 380 %, Freighter 9 %. Sim (`fuel.ts`): `legFuel` (burn × economic distance of distance ÷ origin factor, decision 0.5.95 as the user decided), `plainDistance` (the curve's inverse), `fullTankReach` (factor × plainDistance(tank ÷ burn)), `fuelPriceAt`; `rangeFrom` and `checkRoute` now take the config and use full-tank reach. Until Step 15.4 adds tanks to ships, a trip is still charged at departure: its fuel at the origin's price. API `stats` carry `tankCapacityFu` and `burnFuPerMillionKm` instead of range. Web: the Market's "Range" is now "Reach" (a full tank from Earth), the upgrade screen shows "Tank" in fu. Balance re-check passes: first purchase 64 min, discovery 64, loan 156, four ships 151 vs 158. Tests: `locations.test.ts` (fuel prices ordered Jupiter < Ceres < Moon < Mars < Earth; every base location sells fuel); `fuel.test.ts` (leg fuel, the curve's inverse, full-tank reach burns exactly a tank and scales by the origin factor, the interim cost by hand); the §4 table (`reach-table.test.ts`) now runs on full-tank reach; `courier-mars`, `upgrade-caps` and the content distinctness test in tank form; `ships.test.ts` (the Clipper burns most per M km). Also removed four empty `import {}` lines left by Step 15.2's cleanup.
-- [ ] Step 15.4 — Sim: tank, burn, and refuel
+- [x] **Step 15.4 — Sim: tank, burn, and refuel.** Sim (`fuel.ts`): `Tank` (fuel and weighted average price), `refuel` (up to capacity, new average, whole-credit cost), `affordableRefuel` (the most the credits cover, never over), `legFuelCost` (burned × average price). Ships carry `tank` in `ShipState`; dispatch and deadhead validation fail with `not-enough-fuel` (replacing `insufficient-credits`) when fuel on board is short; proposals no longer take credits. Records gain `fuelBurnedFu`; `fuelCost` is that fuel at the tank's average price (pilot pay uses it, decision 0.5.98); tutorial runs burn none. `tripFuelCost` became `tripFuel` (fu). Resolution takes an optional `fuel` block (tank, capacity, policy, credits) and returns `topUp` (Auto: the most the credits after this delivery cover, at the destination's price; Manual or no tank: none). Pulled forward from 15.6 so the game keeps working: saved ships have `fuelFu`, `fuelAvgPrice`, `refuelPolicy`; save version 2 with the 1 → 2 migration (every ship full at the price where it is, the base price in flight, Auto; old records burned 0 fu, old resolutions no top-up); the engine takes fuel from the tank at departure (no credits) and applies the top-up on landing; Market ships arrive full at the bay's price; the deal's Courier and Clipper come with a quarter tank (`config.deal.tankShare`, user decision: with full tanks the Clipper left for Mars at once and the first purchase moved to 79 min); the API ship carries the fuel fields and summaries carry `topUp`. Web: the sim sees each ship's tank, the dispatch sheet and deadhead picker cost fuel at the average price and say "Not enough fuel (needs N fu, has M fu)". The balance simulator flies tanks too (Auto top-up, refuel before choosing work); results: first purchase 64 min, discovery 49, loan 136, four ships 136 vs 136. Tests: `packages/sim/test/tank.test.ts` (Moon leg = Earth amount at distance ÷ 1.3; 50 fu at 1.0 into 50 fu at 2.0 averages 1.5; never past capacity; affordable refuel exact; record burn and cost; pilot pay from burned × average; Auto top-up to full at the local price; Manual buys nothing; half the credits buys half; the tutorial loaner untouched); `dispatch.test.ts` (`not-enough-fuel`, passes after refuelling); `packages/schema/test/save.test.ts` (1 → 2 migration: tanks full at the right price, Auto, nothing else changed); `packages/engine/test/fuel.test.ts` (Market ship full; deal ships a quarter; burn then Auto top-up with the exact credits; Manual leaves the tank). Updated tests that expected fuel in credits (contract dispatch, deadhead, concurrency, browser 12.4); browser 12.5 fills the Clipper with an Earth–Moon round trip before its Mars run.
 - [ ] Step 15.5 — Sim: stranding and emergency fuel
 - [ ] Step 15.6 — Engine: commands and save migration
 - [ ] Step 15.7 — Client: fuel in the UI

packages/content/src/data/config.ts

@@ -23,7 +23,14 @@ export const gameConfig: GameConfig = {
   loanRepaymentShare: 0.25,
   // The deal (CR-013): Halvorsen's Courier for the avatar, his Clipper for the
   // veteran, and the Earth bay. The loan is computed from their prices.
-  deal: { avatarShipModelId: "courier", veteranShipModelId: "clipper", bayLocationId: "earth" },
+  // The ships come with a quarter tank (CR-015, user decision): the Clipper earns
+  // locally before the player can fuel a Mars run, as before fuel tanks.
+  deal: {
+    avatarShipModelId: "courier",
+    veteranShipModelId: "clipper",
+    bayLocationId: "earth",
+    tankShare: 0.25,
+  },
   contractBoardPeriodRealMinutes: 10,
   // Housekeeping (Step 7.3, CR-014): four hours of boards; a week of seen trips.
   boardRetentionPeriods: 24,

packages/content/src/schemas.ts

@@ -238,6 +238,8 @@ export const gameConfigSchema = z
       avatarShipModelId: z.string().min(1),
       veteranShipModelId: z.string().min(1),
       bayLocationId: z.string().min(1),
+      /** How full the deal's ships' tanks are (CR-015, user decision): Halvorsen's leftovers. */
+      tankShare: fraction,
     }),
     contractBoardPeriodRealMinutes: z.number().positive(),
     /** Past board periods whose boards and accepted contracts are kept (Step 7.3). */

packages/content/test/config.test.ts

@@ -40,6 +40,8 @@ describe("game config", () => {
       avatarShipModelId: "courier",
       veteranShipModelId: "clipper",
       bayLocationId: "earth",
+      // Halvorsen's ships come with a quarter tank (CR-015, user decision).
+      tankShare: 0.25,
     });
     expect(content.dealLoanAmount).toBe(price("courier") + price("clipper") + earth.bayLeasePrice);
   });

packages/content/test/schemas.test.ts

@@ -114,7 +114,12 @@ const validGameConfig = {
   baseFuelPricePerFu: 10,
   emergencyFuelMultiplier: 2.5,
   economicDistance: { referenceMillionKm: 0.384, exponent: 0.6 },
-  deal: { avatarShipModelId: "courier", veteranShipModelId: "clipper", bayLocationId: "earth" },
+  deal: {
+    avatarShipModelId: "courier",
+    veteranShipModelId: "clipper",
+    bayLocationId: "earth",
+    tankShare: 0.25,
+  },
 };
 
 const validScripted = {

packages/engine/src/game/commands.ts

@@ -90,6 +90,8 @@ export function commandTable(): CommandTable {
           break;
         case "reset-upgrades":
           ship.upgrades = {};
+          // A smaller tank holds no more than it can (CR-015).
+          ship.fuelFu = Math.min(ship.fuelFu, content.shipModel(ship.modelId)!.tankCapacityFu);
           break;
         case "finish-shop":
           // Done now: the "out of the shop" note still shows, as for a finished job.

packages/engine/src/game/company.ts

@@ -4,7 +4,7 @@ import type { RealTime } from "@deadhead/sim";
 import type { RandomSource } from "../core";
 import { fail } from "./errors";
 import { companyName, shipName } from "./names";
-import { companyView, isDealAvailable } from "./state";
+import { companyView, deliveredTank, isDealAvailable } from "./state";
 
 export const AVATAR_NAME = "Captain";
 
@@ -121,6 +121,8 @@ export function acceptDeal(save: SaveDocument, random: RandomSource, now: RealTi
       fromDeal: true,
       createdAt: now,
       lastArrivalAt: now,
+      // Halvorsen's ships come with what's left in their tanks (CR-015, user decision).
+      ...deliveredTank(modelId, bayLocationId, content.config.deal.tankShare),
     });
   }
   save.bays.push({ id: random.id(), locationId: bayLocationId, createdAt: now });

packages/engine/src/game/dispatch.ts

@@ -43,7 +43,7 @@ function claimableContract(
   throw fail("unknown-contract", "No such contract on your boards.");
 }
 
-/** Stores a dispatch, marks its contract accepted, and charges fuel. */
+/** Stores a dispatch, marks its contract accepted, and takes the leg's fuel from the tank. */
 function storeDispatch(
   save: SaveDocument,
   args: {
@@ -75,7 +75,7 @@ function storeDispatch(
       acceptedAt: now,
     });
   }
-  save.company.credits -= record.fuelCost;
+  if (shipId !== null) requireShip(save, shipId).fuelFu -= record.fuelBurnedFu;
   return toApiDispatch(dispatch);
 }
 
@@ -85,8 +85,8 @@ function setInFlight(save: SaveDocument, shipId: string, pilotId: string): void
 }
 
 /**
- * The avatar flies the company loaner on a tutorial contract (Step 6.4). The
+ * The avatar flies the company loaner on a tutorial contract (Step 6.4). It
- * company pays fuel, and only one tutorial run may be in flight.
+ * uses no fuel (decision 0.5.94), and only one tutorial run may be in flight.
  */
 export function dispatchTutorial(
   save: SaveDocument,
@@ -112,10 +112,7 @@ export function dispatchTutorial(
     inFlight: false,
   };
   const pilot = pilotState(avatar);
-  const check = validateDispatch(
+  const check = validateDispatch({ ship: loaner, pilot, contract, tutorial: true, now }, content);
-    { ship: loaner, pilot, contract, tutorial: true, credits: save.company.credits, now },
-    content,
-  );
   if (!check.ok) throw fail(check.reason, VALIDATION_MESSAGES[check.reason]);
 
   const record = createDispatchRecord(
@@ -156,7 +153,6 @@ export function dispatchContract(
     // The no-strand rule counts only discovered locations (decision 0.5.79).
     discoveredIds: discoveredIds(save),
     tutorial: false,
-    credits: save.company.credits,
     now,
   };
   const check = validateDispatch(proposal, content);
@@ -185,7 +181,6 @@ export function dispatchReposition(
     pilot: pilotState(pilot),
     destinationId: input.destinationId,
     discoveredIds: discoveredIds(save),
-    credits: save.company.credits,
     now,
   };
   const check = validateReposition(proposal, content);

packages/engine/src/game/fleet.ts

@@ -13,6 +13,7 @@ import { fail } from "./errors";
 import { UPGRADE_MESSAGES, VALIDATION_MESSAGES } from "./messages";
 import { pilotName, shipName } from "./names";
 import {
+  deliveredTank,
   hasBayAt,
   requirePilot,
   requireShip,
@@ -71,6 +72,8 @@ export function buyShip(
     fromDeal: false,
     createdAt: now,
     lastArrivalAt: now,
+    // Delivered with a full tank, included in the price (decision 0.5.94).
+    ...deliveredTank(model.id, bay.locationId),
   };
   save.ships.push(ship);
   return toApiShip(save, ship, now);

packages/engine/src/game/messages.ts

@@ -17,7 +17,7 @@ export const VALIDATION_MESSAGES: Record<DispatchFailure | RepositionFailure, st
   "cargo-skill-too-low": "The pilot's cargo skill is too low for this contract.",
   "long-haul-too-low": "The pilot's Long Haul skill is too low for this distance.",
   "contract-expired": "This contract has expired.",
-  "insufficient-credits": "Not enough credits for fuel.",
+  "not-enough-fuel": "Not enough fuel on board for this leg. Refuel first.",
   "already-there": "The ship is already there.",
   "location-undiscovered": "You can only fly empty to places you have discovered.",
 };

packages/engine/src/game/resolve.ts

@@ -1,11 +1,12 @@
 import { content } from "@deadhead/content";
 import type { SaveDocument } from "@deadhead/schema";
-import { boardPeriodIndex, resolveDispatch, type RealTime } from "@deadhead/sim";
+import { boardPeriodIndex, effectiveStats, resolveDispatch, type RealTime } from "@deadhead/sim";
 import { discoveredIds } from "./state";
 
 /**
  * Resolves every in-flight dispatch that has arrived by `now`, in arrival
- * order (Steps 6.1, 7.2): credits (net of pilot pay and loan repayment), XP,
+ * order (Steps 6.1, 7.2): credits (net of pilot pay and loan repayment), Auto
+ * top-up (CR-015), XP,
  * duty and rest, ship and pilot locations, tutorial progress and discovery.
  * A resolved dispatch is never resolved again, so running this twice in a
  * row changes nothing the second time. Returns how many were resolved.
@@ -21,6 +22,8 @@ export function resolveArrivals(save: SaveDocument, now: RealTime): number {
   for (const dispatch of due) {
     const pilot = save.pilots.find((p) => p.id === dispatch.pilotId);
     if (!pilot) throw new Error(`Dispatch ${dispatch.id} has no pilot`);
+    const ship = dispatch.shipId ? save.ships.find((s) => s.id === dispatch.shipId) : undefined;
+    const model = ship ? content.shipModel(ship.modelId) : undefined;
     const result = resolveDispatch(
       {
         record: dispatch.record,
@@ -31,6 +34,15 @@ export function resolveArrivals(save: SaveDocument, now: RealTime): number {
         pilotDutyHours: pilot.dutyHours,
         pilotSkills: pilot.skills,
         now,
+        fuel:
+          ship && model
+            ? {
+                tank: { fuelFu: ship.fuelFu, avgPrice: ship.fuelAvgPrice },
+                capacityFu: effectiveStats(model, ship.upgrades, content).tankCapacityFu,
+                refuelPolicy: ship.refuelPolicy,
+                credits: save.company.credits,
+              }
+            : undefined,
       },
       content,
     );
@@ -41,6 +53,12 @@ export function resolveArrivals(save: SaveDocument, now: RealTime): number {
     Object.assign(dispatch, { status: "resolved", resolution: r, resolvedAt: now });
     save.company.credits += r.credits;
     save.company.loanBalance -= r.loanRepayment;
+    // Auto top-up on landing (decision 0.5.97).
+    if (r.topUp && ship) {
+      save.company.credits -= r.topUp.cost;
+      ship.fuelFu = r.topUp.tank.fuelFu;
+      ship.fuelAvgPrice = r.topUp.tank.avgPrice;
+    }
 
     pilot.xp += r.pilotXp;
     pilot.status = "idle";
@@ -50,7 +68,6 @@ export function resolveArrivals(save: SaveDocument, now: RealTime): number {
     // Only unassigned pilots store a location (decision 0.5.27): the tutorial avatar.
     if (pilot.assignedShipId === null) pilot.locationId = r.shipLocationId;
 
-    const ship = dispatch.shipId ? save.ships.find((s) => s.id === dispatch.shipId) : undefined;
     if (ship) {
       ship.status = "idle";
       ship.locationId = r.shipLocationId;

packages/engine/src/game/state.ts

@@ -12,6 +12,7 @@ import {
   completedGoals,
   dutyLimit,
   effectiveStats,
+  fuelPriceAt,
   isInShop,
   isResting,
   pilotLevel,
@@ -74,6 +75,23 @@ export function spend(save: SaveDocument, amount: number, what: string): void {
   save.company.credits -= amount;
 }
 
+/** A ship's tank on delivery: `share` of its capacity, bought at `locationId`'s price. */
+export function deliveredTank(
+  modelId: string,
+  locationId: string,
+  share = 1,
+): Pick<SavedShip, "fuelFu" | "fuelAvgPrice" | "refuelPolicy"> {
+  const model = content.shipModel(modelId);
+  const location = content.location(locationId);
+  if (!model || !location)
+    throw new Error(`Unknown ship model or location: ${modelId}, ${locationId}`);
+  return {
+    fuelFu: model.tankCapacityFu * share,
+    fuelAvgPrice: fuelPriceAt(location, content.config),
+    refuelPolicy: "auto",
+  };
+}
+
 export function shipState(ship: SavedShip): ShipState {
   return {
     id: ship.id,
@@ -83,6 +101,7 @@ export function shipState(ship: SavedShip): ShipState {
     inFlight: ship.status === "in-flight",
     upgrades: ship.upgrades,
     inShopUntil: ship.inShopUntil,
+    tank: { fuelFu: ship.fuelFu, avgPrice: ship.fuelAvgPrice },
   };
 }
 
@@ -157,6 +176,9 @@ export function toApiShip(save: SaveDocument, ship: SavedShip, now: RealTime): S
       ship.shopUpgradeId && ship.shopLevel !== null && ship.inShopUntil !== null
         ? { upgradeId: ship.shopUpgradeId, level: ship.shopLevel, until: ship.inShopUntil }
         : null,
+    fuelFu: ship.fuelFu,
+    fuelAvgPrice: ship.fuelAvgPrice,
+    refuelPolicy: ship.refuelPolicy,
   };
 }
 
@@ -234,6 +256,13 @@ export function playerState(save: SaveDocument, now: RealTime): PlayerState {
         tutorial: d.tutorial,
         deadhead: d.record.contract === null,
         fuelCost: d.record.fuelCost,
+        topUp: d.resolution?.topUp
+          ? {
+              locationId: d.resolution.topUp.locationId,
+              boughtFu: d.resolution.topUp.boughtFu,
+              cost: d.resolution.topUp.cost,
+            }
+          : null,
         goodId: d.record.contract?.goodId ?? null,
         massTonnes: d.record.contract?.massTonnes ?? null,
         shipper: d.record.contract?.shipper ?? null,

packages/engine/test/fuel.test.ts

@@ -0,0 +1,96 @@
+import { content } from "@deadhead/content";
+import { fuelPriceAt } from "@deadhead/sim";
+import { describe, expect, it } from "vitest";
+import {
+  edit,
+  getState,
+  putBoard,
+  readSave,
+  setCredits,
+  signUp,
+  signUpOwner,
+  testContract,
+  useTestApp,
+} from "./support";
+
+const testApp = useTestApp();
+const tank = (id: string) => content.shipModel(id)!.tankCapacityFu;
+const price = (id: string) => fuelPriceAt(content.location(id)!, content.config);
+
+describe("fuel tanks in the engine (Step 15.4)", () => {
+  it("delivers a Market ship with a full tank, bought at the bay's price", async () => {
+    const { app } = testApp();
+    const owner = await signUpOwner(app);
+    await setCredits(app, content.shipModel("freighter")!.price);
+    const { ship } = await app.call("buyShip", { modelId: "freighter", bayId: owner.earthBayId });
+    expect(ship).toMatchObject({
+      fuelFu: tank("freighter"),
+      fuelAvgPrice: price("earth"),
+      refuelPolicy: "auto",
+    });
+    // The tank was included in the price.
+    expect((await getState(app)).company.credits).toBe(0);
+  });
+
+  it("hands over the deal's ships with a quarter tank (CR-015, user decision)", async () => {
+    const { app } = testApp();
+    await signUp(app);
+    await edit(app, (save) => {
+      save.player.tutorialRunsCompleted = content.config.tutorialRunsBeforeDeal;
+      save.player.loanerLocationId = "earth";
+    });
+    const state = await app.call("acceptDeal", {});
+    for (const ship of state.ships) {
+      expect(ship.fuelFu, ship.modelId).toBeCloseTo(tank(ship.modelId) * 0.25);
+      expect(ship.fuelAvgPrice).toBe(price("earth"));
+    }
+  });
+
+  it("burns the leg from the tank and, with Auto, tops up on landing at the local price", async () => {
+    const { app, clock } = testApp();
+    const owner = await signUpOwner(app);
+    await setCredits(app, 10_000);
+    const contract = testContract();
+    await putBoard(app, [contract]);
+    const { dispatch } = await app.call("createDispatch", {
+      kind: "contract",
+      contractId: contract.id,
+      shipId: owner.shipId,
+      pilotId: owner.avatarId,
+    });
+    expect((await getState(app)).company.credits).toBe(10_000);
+
+    clock.now = dispatch.arrivalAt;
+    const state = await getState(app);
+    const [summary] = state.summaries;
+    const bought = summary!.topUp!;
+    expect(bought.locationId).toBe("moon");
+    expect(bought.boughtFu).toBeCloseTo(dispatch.fuelBurnedFu);
+    expect(bought.cost).toBe(Math.round(dispatch.fuelBurnedFu * price("moon")));
+    expect(state.company.credits).toBe(10_000 + summary!.credits - bought.cost);
+    expect(state.ships[0]!.fuelFu).toBeCloseTo(tank("courier"));
+  });
+
+  it("leaves the tank as it landed with Manual", async () => {
+    const { app, clock } = testApp();
+    const owner = await signUpOwner(app);
+    await setCredits(app, 10_000);
+    await edit(app, (save) => {
+      save.ships.find((s) => s.id === owner.shipId)!.refuelPolicy = "manual";
+    });
+    const contract = testContract();
+    await putBoard(app, [contract]);
+    const { dispatch } = await app.call("createDispatch", {
+      kind: "contract",
+      contractId: contract.id,
+      shipId: owner.shipId,
+      pilotId: owner.avatarId,
+    });
+    clock.now = dispatch.arrivalAt;
+    const state = await getState(app);
+    expect(state.summaries[0]!.topUp).toBeNull();
+    expect(state.company.credits).toBe(10_000 + state.summaries[0]!.credits);
+    const saved = (await readSave(app)).ships.find((s) => s.id === owner.shipId)!;
+    expect(saved.fuelFu).toBeCloseTo(tank("courier") - dispatch.fuelBurnedFu);
+  });
+});

packages/engine/test/ported/concurrency.test.ts

@@ -67,7 +67,11 @@ describe("concurrency and money safety", () => {
     expect(responses.map((r) => r.statusCode).sort()).toEqual([200, 409]);
     const state = await getState(app, guest);
     expect(state.activeDispatches).toHaveLength(1);
-    expect(state.company.credits).toBe(10_000 - state.activeDispatches[0]!.fuelCost);
+    // One leg's fuel left the tank, once; no credits were charged (CR-015).
+    expect(state.company.credits).toBe(10_000);
+    expect(state.ships[0]!.fuelFu).toBeCloseTo(
+      state.ships[0]!.stats.tankCapacityFu - state.activeDispatches[0]!.fuelBurnedFu,
+    );
   });
 
   it("leases one bay when the same lease is sent twice at once", async () => {

packages/engine/test/ported/contract-dispatch.test.ts

@@ -70,7 +70,7 @@ async function expectRejected(
 }
 
 describe("contract dispatch", () => {
-  it("dispatches, charges fuel, stores the record and removes the contract from the board", async () => {
+  it("dispatches, burns fuel from the tank, stores the record and removes the contract from the board", async () => {
     const { app, clock } = testApp();
     const o = await owner();
     const contract = testContract();
@@ -87,10 +87,14 @@ describe("contract dispatch", () => {
       expectedPayout: contract.payout,
       tutorial: false,
     });
+    expect(record.fuelBurnedFu).toBeGreaterThan(0);
     expect(record.fuelCost).toBeGreaterThan(0);
 
+    // Fuel comes out of the tank; no credits change hands (decision 0.5.94).
     const state = await getState(app, o.guest);
-    expect(state.company.credits).toBe(10_000 - record.fuelCost);
+    expect(state.company.credits).toBe(10_000);
+    const full = content.shipModel("courier")!.tankCapacityFu;
+    expect(state.ships[0]!.fuelFu).toBeCloseTo(full - record.fuelBurnedFu);
     expect(state.ships[0]).toMatchObject({ status: "in-flight", dispatchId: record.id });
     expect(state.pilots[0]!.status).toBe("in-flight");
     const board = contractBoardResponseSchema.parse(
@@ -186,13 +190,15 @@ describe("contract dispatch", () => {
     await expectRejected(o, await dispatch(o, contract.id), "contract-expired");
   });
 
-  it("rejects insufficient-credits", async () => {
+  it("rejects not-enough-fuel (CR-015)", async () => {
     const o = await owner();
     const contract = testContract();
     await putBoard(testApp().app, [contract]);
-    await setCredits(testApp().app, 0);
+    await edit(testApp().app, (save) => {
+      save.ships.find((s) => s.id === o.shipId)!.fuelFu = 0.5;
+    });
     const response = await dispatch(o, contract.id);
-    expect(errorCode(response)).toBe("insufficient-credits");
+    expect(errorCode(response)).toBe("not-enough-fuel");
     expect((await readSave(testApp().app)).dispatches).toEqual([]);
   });
 

packages/engine/test/ported/location-board.test.ts

@@ -91,7 +91,13 @@ describe("location contract boards", () => {
       (contract) =>
         validateDispatch(
           {
-            ship: { id: owner.shipId, modelId: "courier", locationId: "earth", inFlight: false },
+            ship: {
+              id: owner.shipId,
+              modelId: "courier",
+              locationId: "earth",
+              inFlight: false,
+              tank: { fuelFu: content.shipModel("courier")!.tankCapacityFu, avgPrice: 16 },
+            },
             pilot: {
               id: owner.avatarId,
               isAvatar: true,
@@ -102,7 +108,6 @@ describe("location contract boards", () => {
             },
             contract,
             tutorial: false,
-            credits: 1_000_000,
             now: clock.now,
           },
           content,

packages/engine/test/ported/reposition.test.ts

@@ -33,15 +33,19 @@ describe("deadhead dispatch", () => {
     expect(state.bays.map((b) => b.locationId)).toEqual(["earth"]);
     expect(state.ships[0]).toMatchObject({ status: "idle", locationId: "moon" });
     expect(state.pilots[0]).toMatchObject({ status: "idle", locationId: "moon", xp: 0 });
-    expect(state.company.credits).toBe(10_000 - dispatch.fuelCost);
+    // Fuel came out of the tank; landing on Auto top-up bought it back at the Moon (CR-015).
-    // The logbook marks it as a deadhead with its fuel (no payout to show).
+    const [summary] = state.summaries;
     expect(state.summaries).toHaveLength(1);
-    expect(state.summaries[0]).toMatchObject({
+    expect(summary).toMatchObject({
       deadhead: true,
       fuelCost: dispatch.fuelCost,
       credits: 0,
       pilotXp: 0,
+      topUp: { locationId: "moon" },
     });
+    expect(summary!.topUp!.boughtFu).toBeCloseTo(dispatch.fuelBurnedFu);
+    expect(state.company.credits).toBe(10_000 - summary!.topUp!.cost);
+    expect(state.ships[0]!.fuelFu).toBeCloseTo(state.ships[0]!.stats.tankCapacityFu);
   });
 
   it("refuses an undiscovered destination and changes nothing", async () => {

packages/engine/test/support.ts

@@ -24,6 +24,7 @@ import {
   SaveStorage,
   type CommandName,
 } from "../src/index";
+import { deliveredTank } from "../src/game/state";
 
 /**
  * Helpers for the ported server tests (CR-014 Step 14.5): the same names and
@@ -305,10 +306,11 @@ export function makeOwner(
       inShopUntil: null,
       shopUpgradeId: null,
       shopLevel: null,
-      // Stands in for the deal's Courier (not a Market purchase, CR-013).
+      // Stands in for the deal's Courier (not a Market purchase, CR-013), with a full tank.
       fromDeal: true,
       createdAt: TEST_NOW,
       lastArrivalAt: TEST_NOW,
+      ...deliveredTank("courier", "earth"),
     });
     Object.assign(
       save.pilots.find((p) => p.id === avatarId)!,
@@ -370,6 +372,8 @@ export function addShip(
       fromDeal: false,
       createdAt: TEST_NOW,
       lastArrivalAt: TEST_NOW,
+      // A full tank, bought where the ship is (decision 0.5.94).
+      ...deliveredTank(ship.modelId, ship.locationId ?? "earth"),
       ...ship,
     });
   });

packages/schema/package.json

@@ -9,6 +9,7 @@
     "typecheck": "tsc --noEmit"
   },
   "dependencies": {
+    "@deadhead/content": "workspace:*",
     "@deadhead/sim": "workspace:*",
     "zod": "^4.6.5"
   }

packages/schema/src/entities.ts

@@ -66,6 +66,11 @@ export const shipSchema = z.object({
   shop: z
     .object({ upgradeId: idSchema, level: z.number().int().positive(), until: timeSchema })
     .nullable(),
+  /** Fuel on board, in fu, and its average purchase price in credits per fu (CR-015). */
+  fuelFu: z.number().nonnegative(),
+  fuelAvgPrice: z.number().nonnegative(),
+  /** Auto top-up on landing, or Manual (decision 0.5.97). */
+  refuelPolicy: z.enum(["auto", "manual"]),
 });
 export type Ship = z.infer<typeof shipSchema>;
 
@@ -143,6 +148,8 @@ export const dispatchSchema = z.object({
   departureAt: timeSchema,
   arrivalAt: timeSchema,
   distanceMillionKm: z.number().nonnegative(),
+  /** Fuel taken from the tank at departure, in fu (CR-015). */
+  fuelBurnedFu: z.number().nonnegative(),
   fuelCost: credits.nonnegative(),
   expectedPayout: credits,
   seed: z.number().int().nonnegative(),
@@ -161,8 +168,12 @@ export const resolutionSummarySchema = z.object({
   tutorial: z.boolean(),
   /** An empty reposition flight: no cargo, no pay (CR-002). */
   deadhead: z.boolean(),
-  /** Fuel paid at departure. */
+  /** The fuel used, at the tank's average price (decision 0.5.98). */
   fuelCost: credits.nonnegative(),
+  /** Auto top-up on landing (decision 0.5.97), or null. */
+  topUp: z
+    .object({ locationId: idSchema, boughtFu: z.number().positive(), cost: credits.nonnegative() })
+    .nullable(),
   /** What was delivered and for whom (CR-007); null for a deadhead. */
   goodId: idSchema.nullable(),
   massTonnes: z.number().positive().nullable(),

packages/schema/src/save.ts

@@ -1,4 +1,11 @@
-import type { Contract as SimContract, DispatchRecord, Resolution } from "@deadhead/sim";
+import { content } from "@deadhead/content";
+import {
+  effectiveStats,
+  fuelPriceAt,
+  type Contract as SimContract,
+  type DispatchRecord,
+  type Resolution,
+} from "@deadhead/sim";
 import { z } from "zod";
 import { contractSchema, idSchema, timeSchema } from "./entities";
 
@@ -23,14 +30,32 @@ export const dispatchRecordSchema = z.object({
   departureAt: timeSchema,
   arrivalAt: timeSchema,
   distanceMillionKm: z.number().nonnegative(),
+  /** Fuel taken from the tank at departure (CR-015); 0 for tutorial runs and pre-tank trips. */
+  fuelBurnedFu: z.number().nonnegative(),
   fuelCost: credits.nonnegative(),
   expectedPayout: credits,
   seed: z.number().int().nonnegative(),
 });
 
+/** A ship's tank (decision 0.5.94): fuel and its average purchase price. */
+const tankSchema = z.object({
+  fuelFu: z.number().nonnegative(),
+  avgPrice: z.number().nonnegative(),
+});
+
 /** What resolving a dispatch did, kept for the "while you were away" summary. */
 export const resolutionSchema = z.object({
   credits,
+  /** Auto top-up on landing (decision 0.5.97). */
+  topUp: z
+    .object({
+      locationId: idSchema,
+      boughtFu: z.number().positive(),
+      price: z.number().positive(),
+      cost: credits.nonnegative(),
+      tank: tankSchema,
+    })
+    .nullable(),
   pilotPay: credits.nonnegative(),
   loanRepayment: credits.nonnegative(),
   pilotXp: z.number().int().nonnegative(),
@@ -59,6 +84,12 @@ export const savedShipSchema = z.object({
   createdAt: timeSchema,
   /** Its latest resolved arrival (the delivery time if none): picks the default Contracts location. */
   lastArrivalAt: timeSchema,
+  /** Fuel on board, in fu (decision 0.5.94). */
+  fuelFu: z.number().nonnegative(),
+  /** Credits per fu, weighted by what was bought where (decision 0.5.98). */
+  fuelAvgPrice: z.number().nonnegative(),
+  /** Auto top-up on landing, or Manual (decision 0.5.97). */
+  refuelPolicy: z.enum(["auto", "manual"]),
 });
 
 export const savedPilotSchema = z.object({
@@ -104,7 +135,7 @@ export const savedDispatchSchema = z.object({
 });
 
 /** The save version this build writes. Bump it with a new migration. */
-export const CURRENT_SAVE_VERSION = 1;
+export const CURRENT_SAVE_VERSION = 2;
 
 export const saveDocumentSchema = z.object({
   saveVersion: z.literal(CURRENT_SAVE_VERSION),
@@ -167,12 +198,42 @@ export interface SaveMigration {
   migrate(save: Record<string, unknown>): Record<string, unknown>;
 }
 
+type Doc = Record<string, unknown>;
+const records = (value: unknown): Doc[] => (Array.isArray(value) ? (value as Doc[]) : []);
+
 /**
- * Every migration, in order. Version 1 is the first local save format, so
+ * Version 1 → 2 (CR-015 §5, fuel tanks): every ship gets a full tank, bought at
- * there is nothing before it yet; a format change adds `{ from: 1, … }` here
+ * the price where it sits (the base price while in flight), on Auto top-up.
- * and bumps `CURRENT_SAVE_VERSION`.
+ * Earlier trips paid fuel in credits, so their records burned no tank fuel and
+ * their resolutions had no top-up. Arrival times are untouched.
  */
-export const SAVE_MIGRATIONS: readonly SaveMigration[] = [];
+function addFuelTanks(save: Doc): Doc {
+  const { config } = content;
+  const ships = records(save.ships).map((ship) => {
+    const model = content.shipModel(String(ship.modelId));
+    const upgrades = (ship.upgrades ?? {}) as Record<string, number>;
+    const capacity = model ? effectiveStats(model, upgrades, content).tankCapacityFu : 0;
+    const at = ship.locationId ? content.location(String(ship.locationId)) : undefined;
+    return {
+      ...ship,
+      fuelFu: capacity,
+      fuelAvgPrice: at ? fuelPriceAt(at, config) : config.baseFuelPricePerFu,
+      refuelPolicy: "auto",
+    };
+  });
+  const dispatches = records(save.dispatches).map((dispatch) => ({
+    ...dispatch,
+    record: { ...(dispatch.record as Doc), fuelBurnedFu: 0 },
+    resolution: dispatch.resolution ? { ...(dispatch.resolution as Doc), topUp: null } : null,
+  }));
+  return { ...save, ships, dispatches };
+}
+
+/**
+ * Every migration, in order: `from` → `from + 1`. A format change adds one
+ * here and bumps `CURRENT_SAVE_VERSION`.
+ */
+export const SAVE_MIGRATIONS: readonly SaveMigration[] = [{ from: 1, migrate: addFuelTanks }];
 
 export type SaveParse = { ok: true; save: SaveDocument } | { ok: false; error: string };
 type Stepped = { ok: true; save: Record<string, unknown> } | { ok: false; error: string };

packages/schema/test/save-fixture.ts

@@ -39,12 +39,13 @@ export function fullSave(): SaveDocument {
     departureAt: T,
     arrivalAt,
     distanceMillionKm: 0.38,
+    fuelBurnedFu: 7.6,
     fuelCost: 160,
     expectedPayout: 1500,
     seed: 42,
   });
   return {
-    saveVersion: 1,
+    saveVersion: 2,
     saveId: "save-1",
     lastTimeSeen: T + 3_600_000,
     player: {
@@ -70,6 +71,9 @@ export function fullSave(): SaveDocument {
         fromDeal: true,
         createdAt: T,
         lastArrivalAt: T + 200_000,
+        fuelFu: 52.4,
+        fuelAvgPrice: 15.2,
+        refuelPolicy: "auto",
       },
       {
         id: "s2",
@@ -84,6 +88,9 @@ export function fullSave(): SaveDocument {
         fromDeal: true,
         createdAt: T,
         lastArrivalAt: T,
+        fuelFu: 1170,
+        fuelAvgPrice: 16,
+        refuelPolicy: "manual",
       },
     ],
     pilots: [
@@ -157,6 +164,13 @@ export function fullSave(): SaveDocument {
         status: "resolved",
         resolution: {
           credits: 1000,
+          topUp: {
+            locationId: "moon",
+            boughtFu: 7.6,
+            price: 11,
+            cost: 84,
+            tank: { fuelFu: 40, avgPrice: 11 },
+          },
           pilotPay: 0,
           loanRepayment: 340,
           pilotXp: 10,

packages/schema/test/save.test.ts

@@ -11,7 +11,7 @@ import { fullSave } from "./save-fixture";
 describe("save document (Step 14.2)", () => {
   it("validates a fully populated save", () => {
     expect(saveDocumentSchema.safeParse(fullSave()).success).toBe(true);
-    expect(CURRENT_SAVE_VERSION).toBe(1);
+    expect(CURRENT_SAVE_VERSION).toBe(2);
   });
 
   it("rejects an invalid save with a readable error naming the field", () => {
@@ -36,7 +36,7 @@ describe("save document (Step 14.2)", () => {
     if (!future.ok) expect(future.error).toContain("newer version");
   });
 
-  it("migrates a version-1 save to a valid current save", () => {
+  it("reads a current save as it is", () => {
     const result = migrateSave(JSON.parse(JSON.stringify(fullSave())));
     expect(result).toEqual({ ok: true, save: fullSave() });
   });
@@ -56,3 +56,49 @@ describe("save document (Step 14.2)", () => {
     });
   });
 });
+
+/** The fixture as a version-1 save: before fuel tanks (CR-015). */
+type Loose = Record<string, unknown> & {
+  ships: Record<string, unknown>[];
+  dispatches: { record: Record<string, unknown>; resolution: Record<string, unknown> | null }[];
+};
+
+function versionOne(): Record<string, unknown> {
+  const save = JSON.parse(JSON.stringify(fullSave())) as Loose;
+  save.saveVersion = 1;
+  for (const ship of save.ships) {
+    delete ship.fuelFu;
+    delete ship.fuelAvgPrice;
+    delete ship.refuelPolicy;
+  }
+  for (const dispatch of save.dispatches) {
+    delete dispatch.record.fuelBurnedFu;
+    if (dispatch.resolution) delete dispatch.resolution.topUp;
+  }
+  return save;
+}
+
+describe("save migration 1 → 2: fuel tanks (CR-015 §5)", () => {
+  it("fills every ship's tank, on Auto top-up, and changes nothing else", () => {
+    const result = migrateSave(versionOne());
+    if (!result.ok) throw new Error(result.error);
+    const { save } = result;
+    const before = fullSave();
+    expect(save.saveVersion).toBe(2);
+    // The Courier has Extended Fuel Tanks 1 (40 fu × 4.8) and is in flight: the base price.
+    expect(save.ships[0]).toMatchObject({ fuelFu: 192, fuelAvgPrice: 10, refuelPolicy: "auto" });
+    // The Clipper is at Earth: a full 1,170 fu at Earth's 16 cr/fu.
+    expect(save.ships[1]).toMatchObject({ fuelFu: 1170, fuelAvgPrice: 16, refuelPolicy: "auto" });
+    // Earlier trips paid fuel in credits: nothing came out of a tank, nothing topped up.
+    for (const dispatch of save.dispatches) {
+      expect(dispatch.record.fuelBurnedFu).toBe(0);
+      if (dispatch.resolution) expect(dispatch.resolution.topUp).toBeNull();
+    }
+    // In-flight dispatches keep their arrival times; everything else is as it was.
+    expect(save.dispatches.map((d) => d.arrivalAt)).toEqual(
+      before.dispatches.map((d) => d.arrivalAt),
+    );
+    expect(save.company).toEqual(before.company);
+    expect(save.pilots).toEqual(before.pilots);
+  });
+});

packages/schema/test/schemas.test.ts

@@ -69,6 +69,9 @@ const ship = {
   },
   inShopUntil: null,
   shop: { upgradeId: "cargo-bay", level: 1, until: 4_102_444_000_000 },
+  fuelFu: 32.3,
+  fuelAvgPrice: 15.2,
+  refuelPolicy: "auto",
 };
 const pilot = {
   id: "p1",
@@ -118,6 +121,7 @@ const dispatch = {
   departureAt: 4_000_000,
   arrivalAt: 4_130_000,
   distanceMillionKm: 0.39,
+  fuelBurnedFu: 7.8,
   fuelCost: 234,
   expectedPayout: 480,
   seed: 123456,
@@ -134,6 +138,7 @@ const summary = {
   credits: 240,
   deadhead: false,
   fuelCost: 0,
+  topUp: null,
   goodId: "consumer-goods",
   massTonnes: 12,
   shipper: "Pacific Orbital Logistics",

packages/sim/balance/simulate.ts

@@ -10,7 +10,10 @@
  */
 import { content as defaultContent, type ShipModel } from "@deadhead/content";
 import {
+  affordableRefuel,
   boardPeriodIndex,
+  fuelPriceAt,
+  type Tank,
   fullTankReach,
   boardPeriodMs,
   checkRoute,
@@ -31,7 +34,7 @@ import {
   resolveDispatch,
   restEndsAt,
   skillPointsAvailable,
-  tripFuelCost,
+  tripFuel,
   validateDispatch,
   validateReposition,
   validateUpgrade,
@@ -105,6 +108,8 @@ export interface SimulationResult {
 }
 
 interface SimShip extends ShipState {
+  /** Every simulated ship has a tank, on Auto top-up (decision 0.5.97). */
+  tank: Tank;
   upgrades: UpgradeLevels;
   inShopUntil: RealTime | null;
   fromDeal: boolean;
@@ -244,25 +249,32 @@ export function simulate(options: SimulationOptions): SimulationResult {
 
   /** Credits per real minute the company keeps from a contract (payout − fuel − pilot pay). */
   function rate(contract: Contract, stats: ShipModel, pilot: SimPilot): number {
-    const fuel = tripFuelCost(stats, loc(contract.originId), loc(contract.destinationId), config);
+    const origin = loc(contract.originId);
+    const fuel =
+      tripFuel(stats, origin, loc(contract.destinationId), config) * fuelPriceAt(origin, config);
     const pay = pilot.isAvatar ? 0 : pilotShare(contract.payout, fuel, config);
     const tripMs =
       (contractTripGameHours(stats, contract, content) * MS_PER_HOUR) / config.timeCompression;
     return (contract.payout - fuel - pay) / Math.max(1, tripMs / MS_PER_MINUTE);
   }
 
-  /** Contracts this crew may take now; `budget` defaults to the credits on hand. */
+  /** A ship as it would be with a full tank (for "is there any way out" checks). */
-  function eligibleContracts(ship: SimShip, pilot: SimPilot, budget = credits): Contract[] {
+  function filled(ship: SimShip): SimShip {
+    const capacity = effectiveStats(model(ship.modelId), ship.upgrades, content).tankCapacityFu;
+    return { ...ship, tank: { ...ship.tank, fuelFu: capacity } };
+  }
+
+  /** Contracts this crew may take now, with the fuel on board (or a full tank). */
+  function eligibleContracts(ship: SimShip, pilot: SimPilot, fullTank = false): Contract[] {
     if (!discovered.has(ship.locationId)) return [];
     return board(ship.locationId).filter(
       (contract) =>
         validateDispatch(
           {
-            ship,
+            ship: fullTank ? filled(ship) : ship,
             pilot: pilotState(pilot),
             contract,
             tutorial: false,
-            credits: budget,
             now,
             discoveredIds: discovered,
           },
@@ -288,7 +300,7 @@ export function simulate(options: SimulationOptions): SimulationResult {
     );
     if (isResting(pilot.restEndsAt, now)) violate("no-dispatch-while-resting", pilot.id);
     accepted.add(contract.id);
-    credits -= record.fuelCost;
+    ship.tank = { ...ship.tank, fuelFu: ship.tank.fuelFu - record.fuelBurnedFu };
     log(
       `${ship.modelId} ${contract.originId}→${contract.destinationId} ${contract.goodId} ${contract.massTonnes}t pays ${contract.payout}${contract.firstContact ? " FIRST CONTACT" : ""} fuel ${record.fuelCost} arrives +${Math.round((record.arrivalAt - now) / MS_PER_MINUTE)}m  credits ${credits}`,
     );
@@ -304,6 +316,7 @@ export function simulate(options: SimulationOptions): SimulationResult {
     while (flights.length > 0 && flights[0]!.record.arrivalAt <= now) {
       const flight = flights.shift()!;
       const pilot = pilots.find((p) => p.id === flight.pilotId)!;
+      const flightShip = flight.shipId ? ships.find((s) => s.id === flight.shipId)! : undefined;
       const result = resolveDispatch(
         {
           record: flight.record,
@@ -313,6 +326,15 @@ export function simulate(options: SimulationOptions): SimulationResult {
           pilotDutyHours: pilot.dutyHours,
           pilotSkills: pilot.skills,
           now,
+          fuel: flightShip
+            ? {
+                tank: flightShip.tank,
+                capacityFu: effectiveStats(model(flightShip.modelId), flightShip.upgrades, content)
+                  .tankCapacityFu,
+                refuelPolicy: "auto",
+                credits,
+              }
+            : undefined,
         },
         content,
       );
@@ -320,6 +342,10 @@ export function simulate(options: SimulationOptions): SimulationResult {
       const r = result.resolution;
       credits += r.credits;
       loanBalance -= r.loanRepayment;
+      if (r.topUp && flightShip) {
+        credits -= r.topUp.cost;
+        flightShip.tank = r.topUp.tank;
+      }
       pilot.xp += r.pilotXp;
       pilot.inFlight = false;
       pilot.dutyHours = r.pilotDutyHours;
@@ -372,12 +398,12 @@ export function simulate(options: SimulationOptions): SimulationResult {
       inFlight: false,
     };
     const avatar = pilots[0]!;
-    // Company pays fuel; the player keeps the tutorial share: best share per minute.
+    // Tutorial runs use no fuel; the player keeps the tutorial share: best share per minute.
     const best = contracts
       .filter(
         (c) =>
           validateDispatch(
-            { ship: loaner, pilot: pilotState(avatar), contract: c, tutorial: true, credits, now },
+            { ship: loaner, pilot: pilotState(avatar), contract: c, tutorial: true, now },
             content,
           ).ok,
       )
@@ -435,6 +461,11 @@ export function simulate(options: SimulationOptions): SimulationResult {
       modelId,
       locationId,
       inFlight: false,
+      tank: {
+        // Market ships come full; the deal's ships with a quarter tank (CR-015).
+        fuelFu: model(modelId).tankCapacityFu * (fromDeal ? config.deal.tankShare : 1),
+        avgPrice: fuelPriceAt(loc(locationId), config),
+      },
       upgrades: {},
       inShopUntil: null,
       fromDeal,
@@ -553,6 +584,7 @@ export function simulate(options: SimulationOptions): SimulationResult {
       if (!pilot || ship.inFlight || pilot.inFlight || isResting(pilot.restEndsAt, now)) continue;
       if (ship.inShopUntil !== null && ship.inShopUntil > now) continue;
       const stats = effectiveStats(model(ship.modelId), ship.upgrades, content);
+      topUpHere(ship, stats.tankCapacityFu);
       const choices = eligibleContracts(ship, pilot)
         .map((c) => ({ c, value: rate(c, stats, pilot) }))
         .filter((o) => o.value > 0)
@@ -562,25 +594,24 @@ export function simulate(options: SimulationOptions): SimulationResult {
         acted = true;
         continue;
       }
-      const canDeadhead = (to: string, budget: number) =>
+      const canDeadhead = (to: string, fullTank: boolean) =>
         to !== ship.locationId &&
         validateReposition(
           {
-            ship,
+            ship: fullTank ? filled(ship) : ship,
             pilot: pilotState(pilot),
             destinationId: to,
             discoveredIds: discovered,
-            credits: budget,
             now,
           },
           content,
         ).ok;
-      const deadheads = [...discovered].filter((to) => canDeadhead(to, credits));
+      const deadheads = [...discovered].filter((to) => canDeadhead(to, false));
-      // A dead end is no work and no way out whatever the balance (CR-002);
+      // A dead end is no work and no way out even on a full tank (CR-002);
-      // running short of cash is the soft-lock check's business.
+      // running short of cash for fuel is the soft-lock check's business.
       if (
-        eligibleContracts(ship, pilot, Infinity).length === 0 &&
+        eligibleContracts(ship, pilot, true).length === 0 &&
-        ![...discovered].some((to) => canDeadhead(to, Infinity))
+        ![...discovered].some((to) => canDeadhead(to, true))
       ) {
         violate("idle-ship-with-nowhere-to-go", `${ship.id} ${ship.modelId} at ${ship.locationId}`);
       }
@@ -607,7 +638,7 @@ export function simulate(options: SimulationOptions): SimulationResult {
           },
           content,
         );
-        credits -= record.fuelCost;
+        ship.tank = { ...ship.tank, fuelFu: ship.tank.fuelFu - record.fuelBurnedFu };
         ship.inFlight = true;
         pilot.inFlight = true;
         flights.push({ record, shipId: ship.id, pilotId: pilot.id });
@@ -626,6 +657,16 @@ export function simulate(options: SimulationOptions): SimulationResult {
     return acted;
   }
 
+  /** Tops the tank up where the ship is, as far as credits go (the player's "Refuel here first"). */
+  function topUpHere(ship: SimShip, capacityFu: number) {
+    const location = loc(ship.locationId);
+    if (!location.sellsFuel || ship.tank.fuelFu >= capacityFu) return;
+    const bought = affordableRefuel(ship.tank, capacityFu, fuelPriceAt(location, config), credits);
+    if (bought.boughtFu <= 0) return;
+    credits -= bought.cost;
+    ship.tank = bought.tank;
+  }
+
   function checkCashflow() {
     if (tutorialActive || flights.length > 0) return;
     const affordable = ships.some((ship) => {
@@ -635,8 +676,8 @@ export function simulate(options: SimulationOptions): SimulationResult {
         discovered.has(ship.locationId) &&
         board(ship.locationId).some(
           (c) =>
-            tripFuelCost(model(ship.modelId), loc(c.originId), loc(c.destinationId), config) <=
+            tripFuel(model(ship.modelId), loc(c.originId), loc(c.destinationId), config) <=
-            credits,
+            ship.tank.fuelFu + credits / fuelPriceAt(loc(ship.locationId), config),
         )
       );
     });

packages/sim/src/dispatch.ts

@@ -5,7 +5,7 @@ import type { Contract } from "./contract";
 import { routeDistance } from "./distance";
 import { isResting } from "./duty";
 import { checkRoute } from "./eligibility";
-import { fuelCost } from "./fuel";
+import { legFuel, legFuelCost, type Tank } from "./fuel";
 import { checkPilotEligibility, type SkillLevels } from "./pilot";
 import { deriveSeed, type Seed } from "./rng";
 import { travelTimeGameHours } from "./travel";
@@ -20,6 +20,8 @@ export interface ShipState {
   upgrades?: UpgradeLevels;
   /** In the upgrade shop until this real time (decision 0.5.66); absent or null: not. */
   inShopUntil?: RealTime | null;
+  /** The ship's fuel (decision 0.5.94); absent for the tutorial loaner, which uses none. */
+  tank?: Tank;
 }
 
 /** A ship's effective stats: its model plus its upgrades (decision 0.5.63). */
@@ -43,9 +45,8 @@ export interface DispatchProposal {
   ship: ShipState;
   pilot: PilotState;
   contract: Contract;
-  /** Tutorial runs are flown by the avatar in the loaner, and the company pays fuel. */
+  /** Tutorial runs are flown by the avatar in the loaner, and use no fuel (decision 0.5.94). */
   tutorial: boolean;
-  credits: number;
   now: RealTime;
   /**
    * Locations the player has discovered, for the no-strand rule (decision 0.5.79).
@@ -70,7 +71,7 @@ export const DISPATCH_FAILURES = [
   "cargo-skill-too-low",
   "long-haul-too-low",
   "contract-expired",
-  "insufficient-credits",
+  "not-enough-fuel",
 ] as const;
 export type DispatchFailure = (typeof DISPATCH_FAILURES)[number];
 
@@ -88,14 +89,25 @@ export function findLocation(id: string, content: SimContent): Location {
   return location;
 }
 
-/** Fuel charged for a trip, in whole credits. */
+/** Fuel a trip burns from the tank, in fu (decision 0.5.95). */
-export function tripFuelCost(
+export function tripFuel(
   model: ShipModel,
   origin: Location,
   destination: Location,
   config: GameConfig,
 ): number {
-  return Math.round(fuelCost(model, origin, routeDistance(origin, destination), config));
+  return legFuel(model, origin, routeDistance(origin, destination), config);
+}
+
+/** Whether the ship has the fuel on board for this leg (decision 0.5.95). */
+function hasFuelFor(
+  ship: ShipState,
+  model: ShipModel,
+  origin: Location,
+  destination: Location,
+  content: SimContent,
+): boolean {
+  return (ship.tank?.fuelFu ?? 0) >= tripFuel(model, origin, destination, content.config);
 }
 
 const fail = (reason: DispatchFailure): DispatchCheck => ({ ok: false, reason });
@@ -134,7 +146,7 @@ export function wouldStrand(
 
 /** Validates a proposed contract dispatch, returning the first failing reason. */
 export function validateDispatch(proposal: DispatchProposal, content: SimContent): DispatchCheck {
-  const { ship, pilot, contract, tutorial, credits, now } = proposal;
+  const { ship, pilot, contract, tutorial, now } = proposal;
   const model = shipStats(ship, content);
   const origin = findLocation(contract.originId, content);
   const destination = findLocation(contract.destinationId, content);
@@ -171,9 +183,8 @@ export function validateDispatch(proposal: DispatchProposal, content: SimContent
 
   if (now >= contract.expiresAt) return fail("contract-expired");
 
-  if (!tutorial) {
+  if (!tutorial && !hasFuelFor(ship, model, origin, destination, content)) {
-    if (credits < tripFuelCost(model, origin, destination, content.config))
+    return fail("not-enough-fuel");
-      return fail("insufficient-credits");
   }
   return { ok: true };
 }
@@ -189,9 +200,11 @@ export interface DispatchRecord {
   tutorial: boolean;
   departureAt: RealTime;
   arrivalAt: RealTime;
-  /** Route distance at departure, in million km. */
+  /** Route distance, in million km. */
   distanceMillionKm: number;
-  /** Credits charged to the player; 0 for tutorial runs (the company pays). */
+  /** Fuel taken from the tank at departure, in fu; 0 for tutorial runs (decision 0.5.94). */
+  fuelBurnedFu: number;
+  /** That fuel at the tank's average price, in credits (decision 0.5.98); 0 for tutorial runs. */
   fuelCost: number;
   expectedPayout: number;
   /** Seed for anything rolled about this trip. */
@@ -230,6 +243,7 @@ function buildRecord(
   const distance = routeDistance(origin, destination);
   const mass = contract?.massTonnes ?? 0;
   const travelGameMs = travelTimeGameHours(model, distance, mass, config) * MS_PER_HOUR;
+  const burned = tutorial ? 0 : legFuel(model, origin, distance, config);
 
   return {
     id,
@@ -242,7 +256,8 @@ function buildRecord(
     departureAt: now,
     arrivalAt: now + Math.round(travelGameMs / config.timeCompression),
     distanceMillionKm: distance,
-    fuelCost: tutorial ? 0 : tripFuelCost(model, origin, destination, content.config),
+    fuelBurnedFu: burned,
+    fuelCost: ship.tank ? legFuelCost(burned, ship.tank) : 0,
     expectedPayout: contract?.payout ?? 0,
     seed: deriveSeed(worldSeed, `dispatch:${id}`),
   };
@@ -263,7 +278,6 @@ export interface RepositionProposal {
   destinationId: string;
   /** Locations the player has discovered; only these can be deadheaded to (CR-002). */
   discoveredIds: ReadonlySet<string>;
-  credits: number;
   now: RealTime;
 }
 
@@ -279,7 +293,7 @@ export const REPOSITION_FAILURES = [
   "cannot-land",
   "out-of-range",
   "would-strand",
-  "insufficient-credits",
+  "not-enough-fuel",
 ] as const;
 export type RepositionFailure = (typeof REPOSITION_FAILURES)[number];
 
@@ -294,7 +308,7 @@ export function validateReposition(
   proposal: RepositionProposal,
   content: SimContent,
 ): RepositionCheck {
-  const { ship, pilot, destinationId, discoveredIds, credits, now } = proposal;
+  const { ship, pilot, destinationId, discoveredIds, now } = proposal;
   const failWith = (reason: RepositionFailure): RepositionCheck => ({ ok: false, reason });
 
   if (ship.inFlight) return failWith("ship-not-idle");
@@ -314,8 +328,8 @@ export function validateReposition(
     return failWith("would-strand");
   }
 
-  if (credits < tripFuelCost(model, origin, destination, content.config)) {
+  if (!hasFuelFor(ship, model, origin, destination, content)) {
-    return failWith("insufficient-credits");
+    return failWith("not-enough-fuel");
   }
   return { ok: true };
 }

packages/sim/src/fuel.ts

@@ -48,15 +48,50 @@ export function fuelPriceAt(location: Location, config: GameConfig): number {
   return config.baseFuelPricePerFu * location.fuelPrice;
 }
 
-/**
+/** What a ship's tank holds (decision 0.5.94): fuel, and its average purchase price. */
- * Fuel cost in credits for a leg: its fuel at the origin's price. (Step 15.3;
+export interface Tank {
- * Step 15.4 replaces the charge with fuel burned from the ship's tank.)
+  fuelFu: number;
- */
+  /** Credits per fu, weighted by how much was bought at each price (decision 0.5.98). */
-export function fuelCost(
+  avgPrice: number;
-  ship: ShipModel,
+}
-  origin: Location,
+
-  distanceMillionKm: number,
+export interface Refuel {
-  config: GameConfig,
+  tank: Tank;
-): number {
+  boughtFu: number;
-  return legFuel(ship, origin, distanceMillionKm, config) * fuelPriceAt(origin, config);
+  /** Whole credits. */
+  cost: number;
+}
+
+/**
+ * Adds up to `amountFu` at `price`, never past `capacityFu` (decision 0.5.97),
+ * and keeps the tank's weighted average price.
+ */
+export function refuel(tank: Tank, capacityFu: number, amountFu: number, price: number): Refuel {
+  const boughtFu = Math.max(0, Math.min(amountFu, capacityFu - tank.fuelFu));
+  const fuelFu = tank.fuelFu + boughtFu;
+  const avgPrice =
+    fuelFu > 0 ? (tank.fuelFu * tank.avgPrice + boughtFu * price) / fuelFu : tank.avgPrice;
+  return {
+    tank: { fuelFu, avgPrice },
+    boughtFu,
+    cost: Math.min(Math.round(boughtFu * price), Math.ceil(boughtFu * price)),
+  };
+}
+
+/** The most fuel up to a full tank that `credits` can pay for (Auto top-up, decision 0.5.97). */
+export function affordableRefuel(
+  tank: Tank,
+  capacityFu: number,
+  price: number,
+  credits: number,
+): Refuel {
+  const affordable = Math.max(0, credits) / price;
+  const result = refuel(tank, capacityFu, affordable, price);
+  // Rounding never charges more than the player has.
+  return { ...result, cost: Math.min(result.cost, Math.max(0, Math.floor(credits))) };
+}
+
+/** What a leg's fuel cost the player (decision 0.5.98): fu burned × the tank's average price. */
+export function legFuelCost(burnedFu: number, tank: Tank): number {
+  return Math.round(burnedFu * tank.avgPrice);
 }

packages/sim/src/index.ts

@@ -13,12 +13,16 @@ export type { Position } from "./positions";
 export { routeDistance } from "./distance";
 export { travelTimeGameHours } from "./travel";
 export {
+  affordableRefuel,
   economicDistance,
-  fuelCost,
   fuelPriceAt,
   fullTankReach,
   legFuel,
+  legFuelCost,
   plainDistance,
+  refuel,
+  type Refuel,
+  type Tank,
 } from "./fuel";
 
 export { canLandAt, checkRoute, rangeFrom } from "./eligibility";
@@ -49,7 +53,7 @@ export {
   createDispatchRecord,
   createRepositionRecord,
   shipStats,
-  tripFuelCost,
+  tripFuel,
   validateDispatch,
   wouldStrand,
   validateReposition,
@@ -79,7 +83,7 @@ export { splitLoanRepayment } from "./loan";
 export type { LoanSplit } from "./loan";
 
 export { resolveDispatch } from "./resolution";
-export type { Resolution, ResolveInput, ResolveResult } from "./resolution";
+export type { RefuelPolicy, Resolution, ResolveInput, ResolveResult, TopUp } from "./resolution";
 
 export { dutyAfterTrip, dutyLimit, isResting, needsRest, restEndsAt, tripGameHours } from "./duty";
 

packages/sim/src/resolution.ts

@@ -1,18 +1,37 @@
 import type { SimContent } from "./board";
 import type { RealTime } from "./clock";
 import type { DispatchRecord } from "./dispatch";
+import { findLocation } from "./dispatch";
 import { dutyAfterTrip, dutyLimit, needsRest, restEndsAt, tripGameHours } from "./duty";
+import { affordableRefuel, fuelPriceAt, type Tank } from "./fuel";
 import { splitLoanRepayment } from "./loan";
 import { pilotShare } from "./pay";
 import type { SkillLevels } from "./pilot";
 import { deliveryXp } from "./xp";
 
+/** Auto top-up (default) fills the tank on landing; Manual never does (decision 0.5.97). */
+export type RefuelPolicy = "auto" | "manual";
+
+/** Fuel an Auto top-up bought on landing (decision 0.5.97). */
+export interface TopUp {
+  locationId: string;
+  boughtFu: number;
+  /** Credits per fu. */
+  price: number;
+  /** Whole credits, paid on top of the delivery's `credits`. */
+  cost: number;
+  /** The tank afterwards. */
+  tank: Tank;
+}
+
 export interface Resolution {
   /**
-   * Credits to add: payout minus pilot pay, minus the loan repayment.
+   * Credits to add: payout minus pilot pay, minus the loan repayment. Fuel
-   * Fuel was already charged at departure.
+   * came out of the tank at departure; any top-up is `topUp.cost`.
    */
   credits: number;
+  /** Auto top-up on landing, or null (Manual, nothing bought, or no tank). */
+  topUp: TopUp | null;
   /** A hired pilot's share of this delivery's profit; 0 for the avatar, tutorial runs and deadheads (CR-010). */
   pilotPay: number;
   /** Credits that went to the lender out of this payout (decision 0.5.32). */
@@ -42,6 +61,30 @@ export interface ResolveInput {
   pilotDutyHours: number;
   pilotSkills: SkillLevels;
   now: RealTime;
+  /**
+   * The ship's tank on landing, its policy, and the company's credits before this
+   * resolution (Auto top-up buys what they cover). Absent: no top-up (the
+   * tutorial loaner uses no fuel).
+   */
+  fuel?: { tank: Tank; capacityFu: number; refuelPolicy: RefuelPolicy; credits: number };
+}
+
+/** Auto top-up on landing (decision 0.5.97): as much as the credits after this trip cover. */
+function topUpOnLanding(input: ResolveInput, net: number, content: SimContent): TopUp | null {
+  const { fuel, record } = input;
+  if (!fuel || record.tutorial || fuel.refuelPolicy !== "auto") return null;
+  const location = findLocation(record.destinationId, content);
+  if (!location.sellsFuel) return null;
+  const price = fuelPriceAt(location, content.config);
+  const bought = affordableRefuel(fuel.tank, fuel.capacityFu, price, fuel.credits + net);
+  if (bought.boughtFu <= 0) return null;
+  return {
+    locationId: location.id,
+    boughtFu: bought.boughtFu,
+    price,
+    cost: bought.cost,
+    tank: bought.tank,
+  };
 }
 
 /**
@@ -73,6 +116,7 @@ export function resolveDispatch(input: ResolveInput, content: SimContent): Resol
       resolution: {
         ...base,
         credits: 0,
+        topUp: topUpOnLanding(input, 0, content),
         pilotPay: 0,
         loanRepayment: 0,
         pilotXp: 0,
@@ -97,6 +141,7 @@ export function resolveDispatch(input: ResolveInput, content: SimContent): Resol
     resolution: {
       ...base,
       credits: net,
+      topUp: topUpOnLanding(input, net, content),
       pilotPay,
       loanRepayment: repayment,
       pilotXp: deliveryXp(record.distanceMillionKm, contract.tier, content.config),

packages/sim/test/balance.test.ts

@@ -1,7 +1,7 @@
 import { beforeAll, describe, expect, it } from "vitest";
 import { simulate, type Milestones, type SimulationResult } from "../balance/simulate";
 import { content } from "@deadhead/content";
-import { MS_PER_HOUR, tripFuelCost } from "../src/index";
+import { fuelPriceAt, MS_PER_HOUR, tripFuel } from "../src/index";
 
 /**
  * Balance targets (plan Step 12.1 as amended by CR-001 to CR-013), checked on
@@ -72,17 +72,20 @@ describe("balance simulation (Step 12.1)", () => {
   });
 
   it("leaves fuel for at least three Courier runs from Earth after the deal (Step 2.5, measured)", () => {
-    // Step 12.2: the tutorial share and starting credits as actually earned.
+    // Step 12.2: the tutorial share and starting credits as actually earned. Since
+    // CR-015 the deal Courier's quarter tank counts, with credits to buy the rest at Earth.
     const courier = content.shipModel("courier")!;
     const [earth, moon] = [content.location("earth")!, content.location("moon")!];
-    const fuel = tripFuelCost(courier, earth, moon, content.config);
+    const runFu = tripFuel(courier, earth, moon, content.config);
+    const inTank = courier.tankCapacityFu * content.config.deal.tankShare;
+    const earthPrice = fuelPriceAt(earth, content.config);
     for (const result of lighterFirst) {
       expect(result.tutorialRuns).toBe(content.config.tutorialRunsBeforeDeal);
       expect(result.tutorialShareEarned).toBeGreaterThan(0);
       expect(result.creditsAtDeal).toBe(
         content.config.startingCredits + result.tutorialShareEarned,
       );
-      expect(result.creditsAtDeal!).toBeGreaterThanOrEqual(3 * fuel);
+      expect(inTank + result.creditsAtDeal! / earthPrice).toBeGreaterThanOrEqual(3 * runFu);
     }
   });
 

packages/sim/test/dispatch.test.ts

@@ -7,8 +7,12 @@ import {
   type PilotState,
   type ShipState,
   type SimContent,
+  tripFuel,
 } from "../src/index";
 
+/** Fuel enough for any leg in these tests (decision 0.5.94), bought at 10 cr/fu. */
+const PLENTY = { fuelFu: 10_000, avgPrice: 10 };
+
 /** Default content plus a test-only ship that cannot land on atmospheric worlds. */
 const vacuumModel: ShipModel = {
   ...defaultContent.shipModel("courier")!,
@@ -40,7 +44,13 @@ const contract: Contract = {
   expiresAt: Date.parse("2100-01-01T01:00:00Z"),
   firstContact: false,
 };
-const ship: ShipState = { id: "s1", modelId: "courier", locationId: "earth", inFlight: false };
+const ship: ShipState = {
+  id: "s1",
+  modelId: "courier",
+  locationId: "earth",
+  inFlight: false,
+  tank: PLENTY,
+};
 const pilot: PilotState = {
   id: "p1",
   isAvatar: false,
@@ -49,7 +59,7 @@ const pilot: PilotState = {
   skills: {},
   restEndsAt: null,
 };
-const valid: DispatchProposal = { ship, pilot, contract, tutorial: false, credits: 10_000, now };
+const valid: DispatchProposal = { ship, pilot, contract, tutorial: false, now };
 
 const reason = (proposal: DispatchProposal) => {
   const result = validateDispatch(proposal, content);
@@ -123,8 +133,20 @@ describe("dispatch validation", () => {
     expect(reason({ ...valid, now: contract.expiresAt })).toBe("contract-expired");
   });
 
-  it("rejects a dispatch the player cannot afford fuel for", () => {
+  it("rejects a dispatch without the fuel on board, and passes once refueled (Step 15.4)", () => {
-    expect(reason({ ...valid, credits: 0 })).toBe("insufficient-credits");
+    const needed = tripFuel(
+      defaultContent.shipModel("courier")!,
+      defaultContent.location("earth")!,
+      defaultContent.location("moon")!,
+      content.config,
+    );
+    const withFuel = (fuelFu: number) => ({
+      ...valid,
+      ship: { ...ship, tank: { fuelFu, avgPrice: 16 } },
+    });
+    expect(reason(withFuel(needed * 0.99))).toBe("not-enough-fuel");
+    expect(reason({ ...valid, ship: { ...ship, tank: undefined } })).toBe("not-enough-fuel");
+    expect(reason(withFuel(needed))).toBe("valid");
   });
 
   describe("tutorial runs", () => {
@@ -137,8 +159,9 @@ describe("dispatch validation", () => {
     const avatar: PilotState = { ...pilot, id: "avatar", isAvatar: true, assignedShipId: null };
     const tutorial: DispatchProposal = { ...valid, ship: loaner, pilot: avatar, tutorial: true };
 
-    it("accepts the avatar in the loaner without credits for fuel", () => {
+    it("accepts the avatar in the loaner, which carries no fuel (decision 0.5.94)", () => {
-      expect(reason({ ...tutorial, credits: 0 })).toBe("valid");
+      expect(tutorial.ship.tank).toBeUndefined();
+      expect(reason(tutorial)).toBe("valid");
     });
 
     it("rejects a hired pilot in the loaner", () => {

packages/sim/test/duty-dispatch.test.ts

@@ -18,6 +18,9 @@ import {
   type ShipState,
 } from "../src/index";
 
+/** Fuel enough for any leg in these tests (decision 0.5.94), bought at 10 cr/fu. */
+const PLENTY = { fuelFu: 10_000, avgPrice: 10 };
+
 const now = Date.parse("2100-01-01T00:30:00Z");
 const contract: Contract = {
   id: "c1",
@@ -37,7 +40,13 @@ const contract: Contract = {
   expiresAt: Date.parse("2100-01-01T01:00:00Z"),
   firstContact: false,
 };
-const ship: ShipState = { id: "s1", modelId: "courier", locationId: "earth", inFlight: false };
+const ship: ShipState = {
+  id: "s1",
+  modelId: "courier",
+  locationId: "earth",
+  inFlight: false,
+  tank: PLENTY,
+};
 const pilot: PilotState = {
   id: "p1",
   isAvatar: false,
@@ -46,7 +55,7 @@ const pilot: PilotState = {
   skills: {},
   restEndsAt: null,
 };
-const proposal: DispatchProposal = { ship, pilot, contract, tutorial: false, credits: 10_000, now };
+const proposal: DispatchProposal = { ship, pilot, contract, tutorial: false, now };
 const limit = dutyLimit({}, content.config);
 
 const resolveAt = (record: DispatchRecord, dutyBefore: number, at = record.arrivalAt) => {
@@ -78,7 +87,6 @@ describe("duty in validation (Step 10D.3)", () => {
           pilot: { ...pilot, restEndsAt: now + 1 },
           destinationId: "moon",
           discoveredIds: new Set(["earth", "moon"]),
-          credits: 10_000,
           now,
         },
         content,

packages/sim/test/effective-stats.test.ts

@@ -12,6 +12,9 @@ import {
   type ShipState,
 } from "../src/index";
 
+/** Fuel enough for any leg in these tests (decision 0.5.94), bought at 10 cr/fu. */
+const PLENTY = { fuelFu: 10_000, avgPrice: 10 };
+
 const now = Date.parse("2100-01-01T00:30:00Z");
 const courier = content.shipModel("courier")!;
 const freighter = content.shipModel("freighter")!;
@@ -34,7 +37,13 @@ const contract: Contract = {
   expiresAt: Date.parse("2100-01-01T01:00:00Z"),
   firstContact: false,
 };
-const ship: ShipState = { id: "s1", modelId: "courier", locationId: "earth", inFlight: false };
+const ship: ShipState = {
+  id: "s1",
+  modelId: "courier",
+  locationId: "earth",
+  inFlight: false,
+  tank: PLENTY,
+};
 const pilot: PilotState = {
   id: "p1",
   isAvatar: false,
@@ -43,7 +52,7 @@ const pilot: PilotState = {
   skills: {},
   restEndsAt: null,
 };
-const proposal: DispatchProposal = { ship, pilot, contract, tutorial: false, credits: 10_000, now };
+const proposal: DispatchProposal = { ship, pilot, contract, tutorial: false, now };
 const reason = (p: DispatchProposal) => {
   const result = validateDispatch(p, content);
   return result.ok ? "valid" : result.reason;

packages/sim/test/first-contact-fit.test.ts

@@ -7,6 +7,9 @@ import {
   type FleetMember,
 } from "../src/index";
 
+/** Fuel enough for any leg in these tests (decision 0.5.94), bought at 10 cr/fu. */
+const PLENTY = { fuelFu: 10_000, avgPrice: 10 };
+
 const earth = content.location("earth")!;
 const start = Date.parse(content.config.epoch.realStart);
 const firstPeriod = boardPeriodIndex(start, content.config);
@@ -26,7 +29,7 @@ const board = (periodIndex: number, discovered: string[], fleet: FleetMember[])
 const clipperCanFly = (contract: ReturnType<typeof board>[number]) =>
   validateDispatch(
     {
-      ship: { id: "s", modelId: "clipper", locationId: "earth", inFlight: false },
+      ship: { id: "s", modelId: "clipper", locationId: "earth", inFlight: false, tank: PLENTY },
       pilot: {
         id: "p",
         isAvatar: false,
@@ -37,7 +40,6 @@ const clipperCanFly = (contract: ReturnType<typeof board>[number]) =>
       },
       contract,
       tutorial: false,
-      credits: 1e9,
       now: contract.offeredAt,
       discoveredIds: new Set(["earth", "moon"]),
     },

packages/sim/test/flight.test.ts

@@ -7,10 +7,13 @@ import {
   locationPosition,
 } from "../src/index";
 
+/** Fuel enough for any leg in these tests (decision 0.5.94), bought at 10 cr/fu. */
+const PLENTY = { fuelFu: 10_000, avgPrice: 10 };
+
 const record = createRepositionRecord(
   {
     id: "r1",
-    ship: { id: "s1", modelId: "courier", locationId: "earth", inFlight: false },
+    ship: { id: "s1", modelId: "courier", locationId: "earth", inFlight: false, tank: PLENTY },
     pilot: {
       id: "p1",
       isAvatar: false,

packages/sim/test/fuel.test.ts

@@ -2,7 +2,6 @@ import { content } from "@deadhead/content";
 import { describe, expect, it } from "vitest";
 import {
   economicDistance,
-  fuelCost,
   fullTankReach,
   legFuel,
   plainDistance,
@@ -33,24 +32,23 @@ describe("economic distance (decision 0.5.84)", () => {
   });
 });
 
-describe("fuel cost", () => {
+describe("leg fuel", () => {
-  it("costs more Earth→Moon than Moon→Earth for the same ship", () => {
+  it("burns more Earth→Moon than Moon→Earth for the same ship", () => {
     const distance = routeDistance(earth, moon);
-    expect(fuelCost(courier, earth, distance, config)).toBeGreaterThan(
+    expect(legFuel(courier, earth, distance, config)).toBeGreaterThan(
-      fuelCost(courier, moon, distance, config),
+      legFuel(courier, moon, distance, config),
     );
   });
 
   it("scales with economic distance", () => {
-    expect(fuelCost(courier, earth, 10, config) / fuelCost(courier, earth, 5, config)).toBeCloseTo(
+    expect(legFuel(courier, earth, 10, config) / legFuel(courier, earth, 5, config)).toBeCloseTo(
       2 ** exponent,
     );
   });
 
-  it("matches a hand calculation (Step 15.3: the leg's fuel at the origin's price)", () => {
+  it("matches a hand calculation", () => {
-    // 20 fu per M km × economic distance of 0.5M km, at 10 cr/fu × Earth's 1.6.
+    // 20 fu per M km × economic distance of 0.5M km.
-    const expected = 20 * ref * (0.5 / ref) ** exponent * 10 * 1.6;
+    expect(legFuel(courier, earth, 0.5, config)).toBeCloseTo(20 * ref * (0.5 / ref) ** exponent);
-    expect(fuelCost(courier, earth, 0.5, config)).toBeCloseTo(expected);
   });
 });
 

packages/sim/test/loan.test.ts

@@ -8,6 +8,9 @@ import {
   pilotShare,
 } from "../src/index";
 
+/** Fuel enough for any leg in these tests (decision 0.5.94), bought at 10 cr/fu. */
+const PLENTY = { fuelFu: 10_000, avgPrice: 10 };
+
 describe("loan repayment split", () => {
   it("takes min(balance, credits × share), rounded down to whole credits", () => {
     expect(splitLoanRepayment(1000, 5000, 0.3)).toEqual({ repayment: 300, net: 700 });
@@ -61,7 +64,7 @@ describe("resolution with a loan", () => {
   const record = createDispatchRecord(
     {
       id: "d1",
-      ship: { id: "s1", modelId: "courier", locationId: "earth", inFlight: false },
+      ship: { id: "s1", modelId: "courier", locationId: "earth", inFlight: false, tank: PLENTY },
       pilot: {
         id: "p1",
         isAvatar: false,

packages/sim/test/no-strand.test.ts

@@ -14,6 +14,9 @@ import {
   type SimContent,
 } from "../src/index";
 
+/** Fuel enough for any leg in these tests (decision 0.5.94), bought at 10 cr/fu. */
+const PLENTY = { fuelFu: 10_000, avgPrice: 10 };
+
 const loc = (id: string) => content.location(id)!;
 const now = Date.parse("2100-01-01T00:30:00Z");
 const pilot: PilotState = {
@@ -46,13 +49,18 @@ const fixture: SimContent = {
     },
   ],
 };
-const hopper: ShipState = { id: "s1", modelId: "hopper", locationId: "earth", inFlight: false };
+const hopper: ShipState = {
+  id: "s1",
+  modelId: "hopper",
+  locationId: "earth",
+  inFlight: false,
+  tank: PLENTY,
+};
 const proposal: RepositionProposal = {
   ship: hopper,
   pilot,
   destinationId: "moon",
   discoveredIds: new Set(["earth", "moon"]),
-  credits: 100_000,
   now,
 };
 
@@ -86,7 +94,7 @@ describe("no-strand rule (Step 10L.3, decision 0.5.79)", () => {
   });
 
   it("applies to contract dispatches too", () => {
-    const base = { ship: hopper, pilot, contract, tutorial: false, credits: 100_000, now };
+    const base = { ship: hopper, pilot, contract, tutorial: false, now };
     expect(
       validateDispatch({ ...base, discoveredIds: new Set(["earth", "moon"]) }, fixture),
     ).toEqual({ ok: false, reason: "would-strand" });

packages/sim/test/priority.test.ts

@@ -9,6 +9,9 @@ import {
   type Contract,
 } from "../src/index";
 
+/** Fuel enough for any leg in these tests (decision 0.5.94), bought at 10 cr/fu. */
+const PLENTY = { fuelFu: 10_000, avgPrice: 10 };
+
 const earth = content.location("earth")!;
 const moon = content.location("moon")!;
 const periodIndex = 4_000;
@@ -37,7 +40,7 @@ function mailContract(priority: boolean): Contract {
 function check(modelId: string, contract: Contract) {
   return validateDispatch(
     {
-      ship: { id: "s", modelId, locationId: "earth", inFlight: false },
+      ship: { id: "s", modelId, locationId: "earth", inFlight: false, tank: PLENTY },
       pilot: {
         id: "p",
         isAvatar: true,
@@ -48,7 +51,6 @@ function check(modelId: string, contract: Contract) {
       },
       contract,
       tutorial: false,
-      credits: 1_000_000,
       now: offeredAt,
     },
     content,

packages/sim/test/profit-share.test.ts

@@ -13,6 +13,9 @@ import {
   type ShipState,
 } from "../src/index";
 
+/** Fuel enough for any leg in these tests (decision 0.5.94), bought at 10 cr/fu. */
+const PLENTY = { fuelFu: 10_000, avgPrice: 10 };
+
 const now = Date.parse("2100-01-01T00:30:00Z");
 const contract: Contract = {
   id: "c1",
@@ -32,7 +35,13 @@ const contract: Contract = {
   expiresAt: now + 3_600_000,
   firstContact: false,
 };
-const ship: ShipState = { id: "s1", modelId: "courier", locationId: "earth", inFlight: false };
+const ship: ShipState = {
+  id: "s1",
+  modelId: "courier",
+  locationId: "earth",
+  inFlight: false,
+  tank: PLENTY,
+};
 const pilot: PilotState = {
   id: "p1",
   isAvatar: false,

packages/sim/test/record.test.ts

@@ -8,6 +8,9 @@ import {
   type RecordInput,
 } from "../src/index";
 
+/** Fuel enough for any leg in these tests (decision 0.5.94), bought at 10 cr/fu. */
+const PLENTY = { fuelFu: 10_000, avgPrice: 10 };
+
 const now = Date.parse("2100-01-01T00:30:00Z");
 const contract: Contract = {
   id: "c1",
@@ -29,7 +32,7 @@ const contract: Contract = {
 };
 const input: RecordInput = {
   id: "d1",
-  ship: { id: "s1", modelId: "courier", locationId: "earth", inFlight: false },
+  ship: { id: "s1", modelId: "courier", locationId: "earth", inFlight: false, tank: PLENTY },
   pilot: {
     id: "p1",
     isAvatar: false,

packages/sim/test/reposition.test.ts

@@ -8,8 +8,17 @@ import {
   type ShipState,
 } from "../src/index";
 
+/** Fuel enough for any leg in these tests (decision 0.5.94), bought at 10 cr/fu. */
+const PLENTY = { fuelFu: 10_000, avgPrice: 10 };
+
 const now = Date.parse("2100-01-01T00:30:00Z");
-const atEarth: ShipState = { id: "s1", modelId: "courier", locationId: "earth", inFlight: false };
+const atEarth: ShipState = {
+  id: "s1",
+  modelId: "courier",
+  locationId: "earth",
+  inFlight: false,
+  tank: PLENTY,
+};
 const pilot: PilotState = {
   id: "p1",
   isAvatar: false,
@@ -24,7 +33,6 @@ const valid: RepositionProposal = {
   pilot,
   destinationId: "moon",
   discoveredIds: new Set(["earth", "moon"]),
-  credits: 10_000,
   now,
 };
 
@@ -58,8 +66,10 @@ describe("deadhead (fly empty)", () => {
     );
   });
 
-  it("still needs fuel credits, an idle crew and an assigned pilot", () => {
+  it("still needs fuel on board, an idle crew and an assigned pilot", () => {
-    expect(reason({ ...valid, credits: 0 })).toBe("insufficient-credits");
+    expect(reason({ ...valid, ship: { ...atEarth, tank: { fuelFu: 0, avgPrice: 16 } } })).toBe(
+      "not-enough-fuel",
+    );
     expect(reason({ ...valid, ship: { ...atEarth, inFlight: true } })).toBe("ship-not-idle");
     expect(reason({ ...valid, pilot: { ...pilot, inFlight: true } })).toBe("pilot-not-idle");
     expect(reason({ ...valid, pilot: { ...pilot, assignedShipId: null } })).toBe(

packages/sim/test/resolution.test.ts

@@ -11,6 +11,9 @@ import {
   pilotShare,
 } from "../src/index";
 
+/** Fuel enough for any leg in these tests (decision 0.5.94), bought at 10 cr/fu. */
+const PLENTY = { fuelFu: 10_000, avgPrice: 10 };
+
 const now = Date.parse("2100-01-01T00:30:00Z");
 const contract: Contract = {
   id: "c1",
@@ -30,7 +33,13 @@ const contract: Contract = {
   expiresAt: Date.parse("2100-01-01T01:00:00Z"),
   firstContact: false,
 };
-const ship: ShipState = { id: "s1", modelId: "courier", locationId: "earth", inFlight: false };
+const ship: ShipState = {
+  id: "s1",
+  modelId: "courier",
+  locationId: "earth",
+  inFlight: false,
+  tank: PLENTY,
+};
 const pilot: PilotState = {
   id: "p1",
   isAvatar: false,

packages/sim/test/static-routes.test.ts

@@ -3,6 +3,9 @@ import { describe, expect, it } from "vitest";
 import { buildContract } from "../src/board";
 import { createDispatchRecord, type Contract } from "../src/index";
 
+/** Fuel enough for any leg in these tests (decision 0.5.94), bought at 10 cr/fu. */
+const PLENTY = { fuelFu: 10_000, avgPrice: 10 };
+
 const earth = content.location("earth")!;
 const ceres = content.location("ceres-station")!;
 const good = content.goods.find(
@@ -31,7 +34,13 @@ function offered(periodIndex: number): Contract {
 }
 
 function flown(contract: Contract, now: number) {
-  const ship = { id: "s1", modelId: "freighter", locationId: "earth", inFlight: false };
+  const ship = {
+    id: "s1",
+    modelId: "freighter",
+    locationId: "earth",
+    inFlight: false,
+    tank: PLENTY,
+  };
   const pilot = {
     id: "p1",
     isAvatar: false,

packages/sim/test/tank.test.ts

@@ -0,0 +1,168 @@
+import { content } from "@deadhead/content";
+import { describe, expect, it } from "vitest";
+import {
+  affordableRefuel,
+  createDispatchRecord,
+  fuelPriceAt,
+  legFuel,
+  legFuelCost,
+  pilotShare,
+  refuel,
+  resolveDispatch,
+  routeDistance,
+  type Contract,
+  type PilotState,
+  type ResolveInput,
+  type ShipState,
+} from "../src/index";
+
+const { config } = content;
+const courier = content.shipModel("courier")!;
+const [earth, moon] = [content.location("earth")!, content.location("moon")!];
+const now = Date.parse("2100-01-01T00:30:00Z");
+const MOON_PRICE = fuelPriceAt(moon, config);
+
+const contract: Contract = {
+  id: "c1",
+  originId: "earth",
+  destinationId: "moon",
+  cargoTypeId: "standard",
+  goodId: "consumer-goods",
+  shipper: "Pacific Orbital Logistics",
+  priority: false,
+  deliveryWindowGameHours: null,
+  tier: 0,
+  massTonnes: 10,
+  payout: 2000,
+  requiredSkill: null,
+  requiredLongHaulLevel: 0,
+  offeredAt: Date.parse("2100-01-01T00:00:00Z"),
+  expiresAt: Date.parse("2100-01-01T01:00:00Z"),
+  firstContact: false,
+};
+const pilot: PilotState = {
+  id: "p1",
+  isAvatar: false,
+  assignedShipId: "s1",
+  inFlight: false,
+  skills: {},
+  restEndsAt: null,
+};
+/** A Courier at Earth with a full tank bought at Earth's price. */
+const ship: ShipState = {
+  id: "s1",
+  modelId: "courier",
+  locationId: "earth",
+  inFlight: false,
+  tank: { fuelFu: courier.tankCapacityFu, avgPrice: fuelPriceAt(earth, config) },
+};
+const record = createDispatchRecord(
+  { id: "d1", ship, pilot, contract, tutorial: false, now, worldSeed: 7 },
+  content,
+);
+/** The tank on landing: what was left after the leg's fuel came out at departure. */
+const landedTank = { ...ship.tank!, fuelFu: ship.tank!.fuelFu - record.fuelBurnedFu };
+
+function landing(policy: "auto" | "manual", credits: number): ResolveInput {
+  return {
+    record,
+    pilotIsAvatar: false,
+    discoveredIds: new Set(["earth", "moon"]),
+    loanBalance: 0,
+    pilotDutyHours: 0,
+    pilotSkills: {},
+    now: record.arrivalAt,
+    fuel: { tank: landedTank, capacityFu: courier.tankCapacityFu, refuelPolicy: policy, credits },
+  };
+}
+function resolve(input: ResolveInput) {
+  const result = resolveDispatch(input, content);
+  if (result.status !== "resolved") throw new Error("expected a resolution");
+  return result.resolution;
+}
+
+describe("fuel tanks (Step 15.4)", () => {
+  it("burns less from the Moon: the leg is shortened by 1.3 before the pay curve (0.5.95)", () => {
+    const d = routeDistance(earth, moon);
+    // The CR's ÷ 1.3, applied before the economic-distance curve (user decision).
+    expect(legFuel(courier, moon, d, config)).toBeCloseTo(legFuel(courier, earth, d / 1.3, config));
+    expect(legFuel(courier, moon, d, config)).toBeCloseTo(
+      legFuel(courier, earth, d, config) / 1.3 ** config.economicDistance.exponent,
+    );
+  });
+
+  it("averages the price of what is in the tank", () => {
+    const filled = refuel({ fuelFu: 50, avgPrice: 2 }, 200, 50, 1);
+    expect(filled.tank).toEqual({ fuelFu: 100, avgPrice: 1.5 });
+    expect(filled.boughtFu).toBe(50);
+    expect(filled.cost).toBe(50);
+  });
+
+  it("never fills past capacity", () => {
+    const filled = refuel({ fuelFu: 90, avgPrice: 2 }, 100, 50, 1);
+    expect(filled.boughtFu).toBe(10);
+    expect(filled.tank.fuelFu).toBe(100);
+  });
+
+  it("buys exactly what the credits cover, up to a full tank", () => {
+    // Half a tank's worth of credits at 10 cr/fu.
+    const half = affordableRefuel({ fuelFu: 0, avgPrice: 0 }, 100, 10, 500);
+    expect(half.boughtFu).toBe(50);
+    expect(half.cost).toBe(500);
+    expect(affordableRefuel({ fuelFu: 0, avgPrice: 0 }, 100, 10, 5_000).boughtFu).toBe(100);
+    expect(affordableRefuel({ fuelFu: 0, avgPrice: 0 }, 100, 10, 0).boughtFu).toBe(0);
+  });
+
+  it("takes the leg's fuel from the tank and costs it at the tank's average price", () => {
+    const burned = legFuel(courier, earth, routeDistance(earth, moon), config);
+    expect(record.fuelBurnedFu).toBeCloseTo(burned);
+    expect(record.fuelCost).toBe(legFuelCost(burned, ship.tank!));
+    expect(record.fuelCost).toBe(Math.round(burned * 16));
+  });
+
+  it("pays a hired pilot from fuel burned × average price (decision 0.5.98)", () => {
+    expect(resolve(landing("manual", 0)).pilotPay).toBe(
+      pilotShare(contract.payout, record.fuelCost, config),
+    );
+  });
+
+  it("tops up to a full tank on landing with Auto, paying the local price", () => {
+    const { topUp } = resolve(landing("auto", 10_000));
+    expect(topUp).not.toBeNull();
+    expect(topUp!.locationId).toBe("moon");
+    expect(topUp!.tank.fuelFu).toBeCloseTo(courier.tankCapacityFu);
+    expect(topUp!.boughtFu).toBeCloseTo(record.fuelBurnedFu);
+    expect(topUp!.price).toBe(MOON_PRICE);
+    expect(topUp!.cost).toBe(Math.round(record.fuelBurnedFu * MOON_PRICE));
+  });
+
+  it("buys nothing with Manual", () => {
+    expect(resolve(landing("manual", 10_000)).topUp).toBeNull();
+  });
+
+  it("buys only what the credits after this delivery cover", () => {
+    const delivery = resolve(landing("manual", 0)).credits;
+    // Credits that, with this delivery's pay, cover half the fuel burned.
+    const halfCost = (record.fuelBurnedFu / 2) * MOON_PRICE;
+    const { topUp } = resolve(landing("auto", halfCost - delivery));
+    expect(topUp!.boughtFu).toBeCloseTo(record.fuelBurnedFu / 2);
+    expect(topUp!.cost).toBeLessThanOrEqual(Math.floor(halfCost));
+  });
+
+  it("leaves the tutorial loaner's fuel alone", () => {
+    const loaner: ShipState = {
+      id: "loaner",
+      modelId: "company-courier",
+      locationId: "earth",
+      inFlight: false,
+    };
+    const avatar = { ...pilot, id: "avatar", isAvatar: true, assignedShipId: null };
+    const tutorialRun = createDispatchRecord(
+      { id: "t1", ship: loaner, pilot: avatar, contract, tutorial: true, now, worldSeed: 7 },
+      content,
+    );
+    expect(tutorialRun.fuelBurnedFu).toBe(0);
+    expect(tutorialRun.fuelCost).toBe(0);
+    expect(resolve({ ...landing("auto", 10_000), record: tutorialRun }).topUp).toBeNull();
+  });
+});

packages/sim/test/upgrade-validation.test.ts

@@ -11,10 +11,19 @@ import {
   type UpgradeProposal,
 } from "../src/index";
 
+/** Fuel enough for any leg in these tests (decision 0.5.94), bought at 10 cr/fu. */
+const PLENTY = { fuelFu: 10_000, avgPrice: 10 };
+
 const now = Date.parse("2100-01-01T00:30:00Z");
 const freighter = content.shipModel("freighter")!;
 const engines = content.upgrade("engines")!;
-const ship: ShipState = { id: "s1", modelId: "freighter", locationId: "earth", inFlight: false };
+const ship: ShipState = {
+  id: "s1",
+  modelId: "freighter",
+  locationId: "earth",
+  inFlight: false,
+  tank: PLENTY,
+};
 const valid: UpgradeProposal = {
   ship,
   upgrade: engines,
@@ -104,7 +113,6 @@ describe("ships in the shop can't fly (Step 10I.3)", () => {
         pilot,
         contract,
         tutorial: false,
-        credits: 1e6,
         now: time,
       },
       content,

pnpm-lock.yaml

@@ -163,6 +163,9 @@ importers:
 
   packages/schema:
     dependencies:
+      '@deadhead/content':
+        specifier: workspace:*
+        version: link:../content
       '@deadhead/sim':
         specifier: workspace:*
         version: link:../sim