fix: ensure passengers only travel forward on train route

Update passenger generation to only create passengers whose destination
stations are ahead of their origin stations (higher track position).
This prevents passengers from being stranded waiting for backwards travel.

- Exclude final station as possible origin (no stations ahead)
- Filter destination stations to only those with position > origin
- Maintains 40% depot start probability for variety

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

apps/web/src/app/games/complement-race/lib/passengerGenerator.ts

@@ -85,24 +85,25 @@ export function generatePassengers(stations: Station[]): Passenger[] {
     usedCombos.add(comboKey)
 
     // Pick random origin and destination stations (must be different)
+    // Destination must be ahead of origin (higher position on track)
     // 40% chance to start at depot, 60% chance to start at other stations
     let originStation: Station
     let destination: Station
 
     if (Math.random() < 0.4 || stations.length < 3) {
-      // Start at depot
+      // Start at depot (first station)
       originStation = stations[0]
-      // Pick any other station as destination
-      const otherStations = stations.slice(1)
-      destination = otherStations[Math.floor(Math.random() * otherStations.length)]
+      // Pick any station ahead as destination
+      const stationsAhead = stations.slice(1)
+      destination = stationsAhead[Math.floor(Math.random() * stationsAhead.length)]
     } else {
-      // Start at a random non-depot station
-      const nonDepotStations = stations.slice(1)
+      // Start at a random non-depot, non-final station
+      const nonDepotStations = stations.slice(1, -1) // Exclude depot and final station
       originStation = nonDepotStations[Math.floor(Math.random() * nonDepotStations.length)]
 
-      // Pick a different station as destination (can include depot)
-      const possibleDestinations = stations.filter(s => s.id !== originStation.id)
-      destination = possibleDestinations[Math.floor(Math.random() * possibleDestinations.length)]
+      // Pick a station ahead of origin (higher position)
+      const stationsAhead = stations.filter(s => s.position > originStation.position)
+      destination = stationsAhead[Math.floor(Math.random() * stationsAhead.length)]
     }
 
     // 30% chance of urgent