switching paths: two routes to the same square

Builds docs/plans/switching-paths.md. A passing loop can offer two legal
routes between the same two squares, coupling different cars — the engine
only ever found one, an artifact of search order (Reported by Jesse, undo
379). exploreMoves now enumerates every simple route (per-path visited set,
capped at 4000 frontier nodes) and dedupes on outcome — destination, entry
side, and origin-tagged cars — rather than on reaching the square at all.

switch.move gains an optional `via: GridCoord` naming one intermediate
square on the chosen route; absent, it resolves exactly as before, so
every existing save and bot decision replays identically (575/575, then
579/579 with the new tests). Threaded through the label, the action-list
dedupe, the hover highlight (data-route), and the history (trayMoved.via).

Ruling recorded as Gap 14 in docs/rules/open-questions.md: the player may
choose the path; §A.4's "may not go around" a car does not reach a
different track the player declined to enter.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SAt2YCXgd5qCjBcF2x34aK

src/sim/view.ts

@@ -19,6 +19,7 @@ import {
   movesFor,
   ownCutFor,
   portersLeft,
+  selectDestination,
 } from '../engine/apply.ts';
 import {
   ACTION_CARDS,
@@ -736,9 +737,19 @@ export function describeIntent(s: GameState, i: Intent): string {
       const tray = s.trays.get(i.trayId);
       const here = tray?.position.at === 'grid' ? tray.position.coord : null;
       let picks = '';
+      let routeNote = '';
       if (here) {
-        const dest = destinationsFor(s, tray!.position.at === 'grid' ? playerAtSeat(s, tray!.position.seat) : 0, i.trayId, here, i.reverse)
-          .find((d) => d.coord.row === i.to.row && d.coord.col === i.to.col);
+        const dests = destinationsFor(s, tray!.position.at === 'grid' ? playerAtSeat(s, tray!.position.seat) : 0, i.trayId, here, i.reverse);
+        const dest = selectDestination(dests, i.to, i.via);
+        // Two routes to the same square (docs/plans/switching-paths.md) would otherwise print the
+        // identical button twice — "move to (0,0)" and "move to (0,0)" — and the action list drops
+        // duplicate labels, silently discarding the second choice. `via` is the one thing that
+        // differs in the DATA, so it is the one thing safe to print without guessing at scenery
+        // this function has no other reason to know the name of.
+        const atSameSquare = dests.filter((d) => d.coord.row === i.to.row && d.coord.col === i.to.col);
+        if (dest && i.via && atSameSquare.length > 1) {
+          routeNote = ` via ${at(i.via)}`;
+        }
         if (dest && dest.couples.length > 0) {
           /**
            * NAME THE CARS THE CREW SET OUT HERE SEPARATELY. They are at the front of `couples` — the
@@ -756,7 +767,7 @@ export function describeIntent(s: GameState, i: Intent): string {
               : ` — couples ${carsLabel(dest.couples)} on the way${end}`;
         }
       }
-      return `move to ${at(i.to)}${i.reverse ? ' (reverse)' : ''}${picks}`;
+      return `move to ${at(i.to)}${routeNote}${i.reverse ? ' (reverse)' : ''}${picks}`;
     }
     case 'switch.dropCars': {
       /**