v0.6.1 — five of six playtest bugs: one button per train, and a load that has to go somewhere

Gameplay testing on 0.4.9d returned six reports. Five are fixed; the sixth could not be
reproduced and is written up in TODO.md with the two questions that would pin it down.

TWO TRAINS AT ONE PLATFORM ANSWERED TO ONE BUTTON. `porter.board` and `porter.detrain`
carried no tray, so there was one button per platform however many trains stood at it and
the reducer filled the first empty coach on the A/D tracks. `check` and the reducer were not
even asking the same question: `check` skipped a train whose card refuses passenger work and
the reducer did not. Both intents now carry an optional `trayId`, one function resolves the
train and the coach for check/execute/reduce alike, `legal.ts` offers one candidate per train,
and the label names it.

A LOAD COULD BE MADE AND BROKEN WITHOUT GOING ANYWHERE. A Freight House could unload the
boxcar it had just loaded; a platform could detrain the passengers it had just boarded. Full
Revenue at both ends for a movement that never happened. Jesse's rule: a load made anywhere in
an Office Area may not be broken anywhere in that Office Area, ever — it has to be carried to
another district. The load carries the seat that made it (`RollingStock.origin`), stripped by
`pooled` at every yard push. Measured at -0.60 +/- 0.10 Revenue a game (t = -6.1) over 400
paired deals: 78 worse, 3 better, 319 unchanged — free Revenue coming off the board, not a nerf.

THE GROCER'S WAREHOUSE SHIPPED AND THE REFINERY RECEIVED. Both were `flow: 'both'` on the
reading that "Freight House" was a collective term for exactly those two, and therefore what
§9.3 described. The engine has dealt a Freight House CARD since before v0.4.9, so §9.3 names
it and the argument goes. The card set agrees: all three Refinery modifiers grant +1 outbound.
Refinery outbound-only, Grocer's inbound-only, Freight House the one two-way industry — which
leaves exactly the one same-district pairing the rule above refuses.

NOT REPRODUCED: cars left behind when backing up over them. Five layouts tried, including cars
spotted at an industry; every one couples the lot. Three are pinned in `apply.test.ts`. One way
to create such cars was closed anyway — `flyingSwitch` wrote its cut past `carsOn`.

Both published replays that had gone dead were re-recorded; a rules change retires a save, and
`harness.test.ts` is what catches it.

The same change ships as v0.4.9e on the 0.4.9 line, branched from the v0.4.9d commit — the engine
files these fixes touch are identical across the two lines, so the patch applied cleanly both ways.

Also carries the two "Queued 2026-08-22, from playing on StartOS" TODO items that were staged
before this work started (Games in Progress readability, and getting back into a game after
losing a browser). They are notes, and items 9-12 below them are numbered against them.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011nbvwWMef8CuEP6t5cgkTv

src/engine/state.ts

@@ -55,7 +55,47 @@ export function coordKey(c: GridCoord): string {
 // ---------------------------------------------------------------------------
 
 /** §2.2 — a coloured car is loaded, a white car is empty. */
-export type RollingStock = { type: CarType; loaded: boolean };
+export type RollingStock = {
+  type: CarType;
+  loaded: boolean;
+  /**
+   * WHICH OFFICE AREA MADE THIS LOAD — the physical game's chip turned upside down in the tray.
+   *
+   * Reported from playtesting v0.4.9d as two bugs with one cause: a boxcar loaded at a Freight
+   * House could be unloaded at that same Freight House on the next Laborer action, and passengers
+   * who had just boarded could be detrained again before the train turned a wheel. Both paid full
+   * Revenue at each end for a load that never went anywhere.
+   *
+   * Jesse's rule (v0.4.9e): freight or passengers loaded anywhere in an Office Area may not be
+   * unloaded ANYWHERE in that same Office Area — not at another facility, not in a later Stage.
+   * They have to be carried by a train to a different Office Area. So the stamp is the SEAT, which
+   * is what an Office Area belongs to (Employee Rotation moves players between chairs; the district
+   * stays with the chair), and it never expires.
+   *
+   * A SEAT, NOT A PLAYER, and undefined rather than -1 for "no origin": the Division Yard opens with
+   * loaded cars and loaded coaches that were made up off-Division (`ROLLING_STOCK_SUPPLY`), and
+   * those are exactly the inbound traffic a solitaire district lives on. A sentinel inside
+   * `SeatIndex`'s own value range is not a sentinel — see `card.play`'s `node` in intents.ts.
+   *
+   * Stripped by `pooled` whenever a car goes back to a yard: the stamp belongs to the LOAD, and a
+   * car returning to the common supply is carrying nothing.
+   */
+  origin?: SeatIndex;
+};
+
+/**
+ * A car returning to the common pool — the Division or Classification Yard — with its load's origin
+ * stamp taken off.
+ *
+ * Every yard push goes through this. A loaded car CAN reach a yard still loaded (a train retires at
+ * a Division Point with freight aboard, `advance.ts`), and without this it would carry a stamp from
+ * a district it left several Days ago into whatever train is made up from it next.
+ */
+export function pooled(car: RollingStock): RollingStock {
+  if (car.origin === undefined) return car;
+  const { origin: _origin, ...rest } = car;
+  return rest;
+}
 
 // ---------------------------------------------------------------------------
 // Track and Office Area