Extras that must run loaded, and a circus paid per district (Gitea#13)

"I've redefined some of the extra trains that they have to run full boxcars —
military trains, circus trains, etc. If not loaded, then empty, and if none
available, run without."

MAKE-UP. X17 Campaign, X18 Circus and X19 Military carry `mustRunLoaded`. It is a
preference order rather than a flat requirement, so the rule is asked of the
DIVISION YARD: an empty is refused only while the yard can still supply a loaded
car this train would accept, and once it cannot, the empty is legal and the train
may still depart short. Per category, since that is the slot the car competes for
— a loaded coach is no reason to refuse an empty boxcar.

SCORING, per Jesse's ruling (2026-08-29): "once per stop in an office area. In a
multiplayer game, each player could score if the circus stops in their area." So
`stopPointClaimed` (a boolean, once per game) becomes `stopPointSeats` (the seats
already paid). A Circus touring three districts is paid three times; one parked in
the same district all game is paid once. The other half of the ruling — "if the
circus train gets recycled and played a second time as a second extra, then it
could again score points later too" — needs no code: a train is made up onto a
fresh tray every time, so a re-played Extra starts with an empty list.

The point now requires the train to be FULLY LOADED, meaning every non-caboose car
loaded. A coach counts as loaded when occupied, which is what makes this the right
test for the Campaign Train: X17 carries one coach and no freight, so "fully
loaded" is exactly "the candidate is aboard". X17 also GAINS the per-stop point —
it had `stopThenExpedite` and no scoring rule at all, and Jesse's "credit for a
circus or campaign train (one point per stop)" says it should score.

TWO BUGS FIXED ALONG THE WAY:

  - `ConsistSpec.emptiesOnly` was declared on X13 Appleseed, RENDERED to the player
    as "(empties only)" by both web/game.ts and sim/view.ts, and enforced by
    nothing — `acceptsCar` never read it, so the Appleseed could be made up loaded
    while its own card said otherwise. It is the same rule as this issue pointing
    the other way, and it would have been perverse to add one and leave the other.
  - Setting up out on the Mainline paid a point to PLAYER 0 whoever was playing:
    `playerAtSeat` needs a seat, off the grid there is none, and the fallback was
    `0`. Scoping the rule to Office Areas is what the ruling says and removes the
    misattribution rather than patching it.

Both loading rules exempt the caboose: every caboose in ROLLING_STOCK_SUPPLY is
minted loaded, so an unexempted rule would bar the one car a consist lists by name.

`trainNeedingCars` now asks the full question per car rather than the shape
question. It shares its predicate with `check` precisely to avoid the stall its own
comment describes, and the shape question stopped being the same question: an
empties-only train facing a yard of loaded cars would have been told a car was
available and then refused every one.

The two published replays that stopped replaying under the new rules were retired
and re-recorded with save-replay.ts, which verifies each candidate before writing
it. That is what test/harness.test.ts is for and what its comment prescribes.

846 tests pass.

Closes #13

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EAgJSmeV8zrMh55Mj85ESb

src/engine/apply.ts

@@ -1159,7 +1159,7 @@ export function check(s: GameState, player: PlayerIndex, i: Intent): RejectionCo
       // This was not enforced at all: any car could be added in any quantity, so Train 9 "Heavy
       // Freight" — a card calling for 3 freight AND a caboose — was made up with four hoppers and
       // no caboose. Fewer is allowed; more, or of the wrong category, is not.
-      return acceptsCar(tray, i.carType) ? null : 'NO_SUITABLE_CAR';
+      return acceptsCar(tray, i.carType, i.loaded, s.yards.divisionYard) ? null : 'NO_SUITABLE_CAR';
     }
 
     case 'newTrain.secondSection': {
@@ -2996,7 +2996,20 @@ function extendLimitsIfNeeded(area: OfficeArea, placed: GridCoord): void {
  * this. A second copy stalled the game outright: the phase believed a car could be added while
  * `check` rejected every option, so the Stage never completed.
  */
-export function acceptsCar(tray: CrewTray, carType: CarType): boolean {
+export function acceptsCar(
+  tray: CrewTray,
+  carType: CarType,
+  /**
+   * Whether the car being offered is loaded, and what the Division Yard still holds.
+   *
+   * Both optional so that a caller asking the SHAPE question — "does this card take a car of this
+   * category at all?" — need not answer the loading question. `trainNeedingCars` asks the shape
+   * question of every car in the yard; `check` asks the full one about a specific car a player has
+   * named. Omitting them skips the loading rules rather than guessing at them.
+   */
+  loaded?: boolean,
+  yard?: readonly RollingStock[],
+): boolean {
   const profile = trainProfile(tray.trainNumber ?? 0, tray.trainIsExtra);
   if (!profile) return true;
 
@@ -3019,6 +3032,40 @@ export function acceptsCar(tray: CrewTray, carType: CarType): boolean {
   const types = profile.consist.freightTypes;
   if (adding === 'freight' && types && !types.includes(carType)) return false;
 
+  if (loaded === undefined) return true;
+
+  /**
+   * X13 APPLESEED — "may drop MTs but not pick up anything", and its consist prints EMPTIES ONLY.
+   *
+   * `emptiesOnly` was declared on the card, RENDERED to the player as "(empties only)" by both
+   * `web/game.ts` and `sim/view.ts`, and enforced by nothing: the Appleseed could be made up with
+   * loaded cars while its own card said it could not. Found while building Gitea#13, which is the
+   * same rule pointing the other way, and fixed with it rather than left as the odd one out.
+   *
+   * A caboose is exempt. Every caboose in `ROLLING_STOCK_SUPPLY` is `loaded: true` — there is no
+   * such thing as an empty one — so applying this to the caboose would bar the Appleseed from the
+   * caboose its own consist calls for.
+   */
+  if (profile.consist.emptiesOnly && loaded && adding !== 'caboose') return false;
+
+  /**
+   * MUST RUN LOADED (Gitea#13) — a preference order, not a flat requirement.
+   *
+   * "If not loaded, then empty, and if none available, run without." So an EMPTY is refused only
+   * while the yard can still supply a loaded car this train would accept; once it cannot, the empty
+   * becomes legal and the train may also simply depart short. Asked of the yard rather than
+   * remembered on the tray, because the yard is what the rule is about and it changes under the
+   * train as other consists are built.
+   *
+   * The caboose is exempt for the same reason as above.
+   */
+  if (profile.rules.mustRunLoaded && !loaded && adding !== 'caboose' && yard) {
+    const loadedAvailable = yard.some(
+      (c) => c.loaded && cat(c.type) === adding && acceptsCar(tray, c.type),
+    );
+    if (loadedAvailable) return false;
+  }
+
   return true;
 }
 
@@ -3059,11 +3106,21 @@ export function isBeingMadeUp(tray: CrewTray): boolean {
 export function trainNeedingCars(s: GameState): TrayId | null {
   for (const [id, tray] of s.trays) {
     if (!isBeingMadeUp(tray)) continue;
-    // Consists are specified by CATEGORY — "Freight (2)" is any two freight cars — so any car in
-    // the yard is potentially suitable unless the card narrows it. Ask the SAME predicate `check`
-    // uses: a separate copy of this test stalled the game, because the phase believed a car could
-    // be added while `check` rejected every option, so the Stage never ended.
-    if (s.yards.divisionYard.some((c) => acceptsCar(tray, c.type))) return id;
+    /**
+     * Consists are specified by CATEGORY — "Freight (2)" is any two freight cars — so any car in
+     * the yard is potentially suitable unless the card narrows it. Ask the SAME predicate `check`
+     * uses: a separate copy of this test stalled the game, because the phase believed a car could
+     * be added while `check` rejected every option, so the Stage never ended.
+     *
+     * ASKED PER CAR, WITH ITS LOADED STATE, since Gitea#13. The shape question alone is no longer
+     * the same question `check` answers: an `emptiesOnly` train looking at a yard of nothing but
+     * loaded cars, or a `mustRunLoaded` train offered only empties while loaded ones remain, would
+     * both be told a car was available and then refused every one of them — the very stall this
+     * comment was written about.
+     */
+    if (s.yards.divisionYard.some((c) => acceptsCar(tray, c.type, c.loaded, s.yards.divisionYard))) {
+      return id;
+    }
   }
   return null;
 }