fix tracks to all be EW. no more NS tracks

src/engine/state.ts

@@ -48,39 +48,47 @@ export type RollingStock = { type: CarType; loaded: boolean };
  * A turnout's handedness: the stem is §A.1's "A", the two legs are "B" and "C". The rule that
  * matters is that `through` and `diverge` are NOT joined to each other.
  *
- * OPEN (Gap 11) — the rules specify "turnout ×6" without saying how many face which way. Until
- * that is settled, orientation is carried per card and defaults to stem-east / diverge-north.
+ * The through track is ALWAYS east-west (`{stem, through}` is `{e,w}`); the diverging leg is the
+ * 45° one and always reaches north or south. Which of the two the card can be turned to is decided
+ * by its printed handedness — see `Slope`.
  */
 export type TurnoutOrientation = { stem: 'n' | 's' | 'e' | 'w'; through: 'n' | 's' | 'e' | 'w'; diverge: 'n' | 's' | 'e' | 'w' };
 
 /**
- * A straight card's axis. Also part of Gap 11 — the catalogue says "straight ×3" without saying
- * how many run each way, yet a layout with no north-south straight can never use the Office's
- * junction stubs at all.
- */
-/**
- * A curve joins two ADJACENT edges. There are exactly four such arcs, and a card can be turned to
- * any of them — which is what makes a siding possible: an arc reaching NORTH is the only way back
- * up to the Running Track from the district below.
+ * A curve joins two ADJACENT edges: it runs along the card's centre line from the east or west edge
+ * to a frog, then leaves at 45° through the MIDDLE of the north or south edge. Four such arcs
+ * exist, but a printed card reaches only two of them (`Slope`).
  */
 export type TrackArc = 'ne' | 'nw' | 'se' | 'sw';
 
-export type TrackAxis = 'ew' | 'ns';
+/**
+ * WHICH DIAGONAL A 45° LEG LIES ON.
+ *
+ * The printed cards (docs/tracks.png) put the through rail dead centre and send every diverging leg
+ * out at 45° through the middle of the north or south edge. A card can be turned 180° but not
+ * flipped over, so its leg never changes diagonal: the slope is printed, not chosen.
+ *
+ * Each name is the pair of arcs that MATE across a horizontal card edge — an `sw` card sitting
+ * above an `ne` card is one unbroken rail, whereas `sw` above `nw` is a V and joins nothing. That
+ * is the whole matching rule, and it is why the name is spelt this way.
+ *
+ * On screen `ne_sw` descends to the right and `nw_se` descends to the left.
+ */
+export type Slope = 'ne_sw' | 'nw_se';
 
 export type CardGeometry =
   | {
       kind: 'track';
       geometry: TrackGeometry;
       turnout?: TurnoutOrientation;
-      axis?: TrackAxis;
       /** Which two edges a CURVE joins — chosen on placement, since the card can be turned. */
       arc?: TrackArc;
-      /** Curves are printed left- or right-handed (design supply); not chosen on placement. */
+      /** Curves and turnouts are printed left- or right-handed, which fixes their `Slope`. */
       hand?: 'left' | 'right';
     }
   | { kind: 'office' }
   | { kind: 'limits' }
-  | { kind: 'facility'; facility: FreightKind; axis?: TrackAxis }
+  | { kind: 'facility'; facility: FreightKind }
   /** Not track — a Modifier sits beside a Facility and raises its capacity (§9). */
   | { kind: 'modifier'; modifier: ModifierKind }
   /** Not track — a Space-use card played at a district to consume a cell (Q6). */