feat: Add device-specific isolation for player IDs

- Add device ID generation (unique per device, stored in localStorage)
- Extend player ID format to: {basePlayerId}:{deviceId}
- Enable cross-domain sync on same device while keeping devices isolated
- Update backend APIs to support new player ID format
- Maintain backward compatibility with legacy UUID format

This allows:
- Each device (Desktop, Android, iOS) to have separate game states
- Cross-domain sync still works on the same device (hoerdle.de ↔ hördle.de)
- Easier debugging with visible device ID in player identifier

app/api/player-id/suggest/route.ts

@@ -6,19 +6,21 @@ const prisma = new PrismaClient();
 /**
  * POST /api/player-id/suggest
  * 
- * Tries to find a player ID based on recently updated states for a genre.
- * This helps synchronize player IDs across different domains (hoerdle.de and hördle.de).
+ * Tries to find a base player ID based on recently updated states for a genre and device.
+ * This helps synchronize player IDs across different domains (hoerdle.de and hördle.de)
+ * on the same device.
  * 
  * Request body:
  * - genreKey: Genre key (e.g., "global", "Rock", "special:00725")
+ * - deviceId: Device identifier (UUID)
  * 
  * Returns:
- * - playerId: Suggested player ID (UUID) if found, null otherwise
+ * - basePlayerId: Suggested base player ID (UUID) if found, null otherwise
  */
 export async function POST(request: Request) {
     try {
         const body = await request.json();
-        const { genreKey } = body;
+        const { genreKey, deviceId } = body;
 
         if (!genreKey || typeof genreKey !== 'string') {
             return NextResponse.json(
@@ -32,6 +34,41 @@ export async function POST(request: Request) {
         const cutoffDate = new Date();
         cutoffDate.setHours(cutoffDate.getHours() - 48);
 
+        // If deviceId is provided, search for states with matching device ID
+        // Format: {basePlayerId}:{deviceId}
+        if (deviceId && typeof deviceId === 'string') {
+            // Search for states with the same device ID
+            const recentStates = await prisma.playerState.findMany({
+                where: {
+                    genreKey: genreKey,
+                    lastPlayed: {
+                        gte: cutoffDate,
+                    },
+                    identifier: {
+                        endsWith: `:${deviceId}`,
+                    },
+                },
+                orderBy: {
+                    lastPlayed: 'desc',
+                },
+                take: 1,
+            });
+
+            if (recentStates.length > 0) {
+                const recentState = recentStates[0];
+                // Extract base player ID from full identifier
+                const colonIndex = recentState.identifier.indexOf(':');
+                if (colonIndex !== -1) {
+                    const basePlayerId = recentState.identifier.substring(0, colonIndex);
+                    return NextResponse.json({
+                        basePlayerId: basePlayerId,
+                        lastPlayed: recentState.lastPlayed,
+                    });
+                }
+            }
+        }
+
+        // Fallback: Find any recent state for this genre (legacy support)
         const recentState = await prisma.playerState.findFirst({
             where: {
                 genreKey: genreKey,
@@ -45,16 +82,26 @@ export async function POST(request: Request) {
         });
 
         if (recentState) {
-            // Return the player ID from the most recent state
-            return NextResponse.json({
-                playerId: recentState.identifier,
-                lastPlayed: recentState.lastPlayed,
-            });
+            // Extract base player ID if format is basePlayerId:deviceId
+            const colonIndex = recentState.identifier.indexOf(':');
+            if (colonIndex !== -1) {
+                const basePlayerId = recentState.identifier.substring(0, colonIndex);
+                return NextResponse.json({
+                    basePlayerId: basePlayerId,
+                    lastPlayed: recentState.lastPlayed,
+                });
+            } else {
+                // Legacy format: return as-is
+                return NextResponse.json({
+                    basePlayerId: recentState.identifier,
+                    lastPlayed: recentState.lastPlayed,
+                });
+            }
         }
 
         // No recent state found
         return NextResponse.json({
-            playerId: null,
+            basePlayerId: null,
         });
     } catch (error) {
         console.error('[player-id/suggest] Error finding player ID:', error);