v0.4.9d — three playtest bugs: a train that looked gone, an unload that ignored the pick, a hang that wasn't one

Patched directly onto 0.4.9a rather than the in-progress 0.5.0 line.

A switching train vanished from the board the moment it left the Office. `selectedTrain` in
`officeSvg` (board-svg.ts), which gates whether a card draws a train's crew badge, was only ever
assigned inside the `cell.adTracks !== null` branch — true for the Office card alone. A train
standing anywhere else, which is everywhere it stands while actually being switched, drew no badge
at all. Game state was never affected; confirmed against the reported save with the engine directly.
Fix hoists the assignment out of the guard so it runs for any card with a train on it.

Unloading always took the westmost car, whichever one was picked. `laborer.beginUnload` carried the
player's chosen `carIndex`, and `check()` validated that specific car, but the `unloadBegan` event
it produced carried only the car's type — the reducer that performs the swap re-derived the target
with `industryTrack.cars.findIndex(c => c.loaded)`, which always answers the first loaded car in
track order regardless of what was requested. Fix adds `carIndex` to the event and uses it directly.

A legal decision could render with zero buttons, which looked exactly like a hang. The "where does
this Extra start" decision is titled by `trainCardTitle`, beginning "Making up Extra X22…" — the
same prefix `renderActions()` stripped from the action list on the assumption it only ever belonged
to the separate yard-chip car-placement panel. With no tray yet being filled, that panel is null, so
nothing rendered the Extra's decision either: a legal, correctly-computed option with no button
anywhere on the page. Replaying the reported save found no engine deadlock at any step — the engine
always had a move. Fix matches the exact title of the one group the yard-chip panel covers instead
of a title-prefix regex.

New tests for all three: a train parked on an ordinary facility card must draw its crew badge; three
differently-typed loaded cars, unloading index 2, must leave indices 0 and 1 alone; the existing
softlock regression test now mirrors the real render filter instead of only the raw menu, plus a
deterministic test for the exact reported scenario. 590 tests, 0 failures.

src/sim/board-svg.ts

@@ -568,13 +568,21 @@ export function officeSvg(
      * Selected train's chip is lit the same amber the crew strip and action buttons already use,
      * and it is the one whose consist is drawn at the rail below. Every occupied chip carries
      * `data-crew`, so the play page can wire a click to switch which train that is.
+     *
+     * COMPUTED FOR EVERY CARD, NOT JUST THE OFFICE. This used to sit inside the `adTracks !== null`
+     * branch below, so it was only ever assigned on the Office card — a train standing anywhere else
+     * in the district (which is everywhere it stands while actually being switched) got no chip at
+     * all: no label, no engine arrow, and no cars drawn, though the game state never lost it. REPORTED:
+     * dropping a car at the Freight House made "the train vanish off the face of the earth" — it had
+     * simply left the one square this code drew a crew on. The Office is the only square that can hold
+     * more than one train, so `cell.trains[0]` is exactly right everywhere else too.
      */
-    let selectedTrain: CellView['trains'][number] | null = null;
+    const selectedTrain: CellView['trains'][number] | null =
+      cell.trains.find((t) => t.trayId === selectedTrayId) ?? cell.trains[0] ?? null;
     if (cell.adTracks !== null) {
       const adTracks = cell.adTracks;
       const gaps = Math.max(0, adTracks - 1);
       const chipW = Math.min(52, (W - 12 - 4 * gaps) / adTracks);
-      selectedTrain = cell.trains.find((t) => t.trayId === selectedTrayId) ?? cell.trains[0] ?? null;
       for (let i = 0; i < adTracks; i++) {
         const train = cell.trains[i] ?? null;
         const cx = 6 + i * (chipW + 4);