fix: pass player IDs (not user IDs) in all arcade game moves

All game moves now explicitly include the database player ID (avatar ID)
in the playerId field. This fixes multiplayer turn validation which was
failing because it was comparing database player IDs with guest IDs.

- FLIP_CARD: Use state.currentPlayer (database player ID)
- START_GAME/resetGame: Use first active player ID, with validation
- CLEAR_MISMATCH: Use state.currentPlayer

Removed fallback to viewerId which incorrectly conflated user/guest IDs
with player IDs.

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

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

apps/web/src/app/arcade/matching/context/ArcadeMemoryPairsContext.tsx

@@ -126,13 +126,14 @@ export function ArcadeMemoryPairsProvider({ children }: { children: ReactNode })
       const timeout = setTimeout(() => {
         sendMove({
           type: 'CLEAR_MISMATCH',
+          playerId: state.currentPlayer, // Use current player ID for CLEAR_MISMATCH
           data: {}
         })
       }, 1500)
 
       return () => clearTimeout(timeout)
     }
-  }, [state.showMismatchFeedback, state.flippedCards.length, sendMove])
+  }, [state.showMismatchFeedback, state.flippedCards.length, sendMove, state.currentPlayer])
 
   // Computed values
   const isGameActive = state.gamePhase === 'playing'
@@ -165,9 +166,18 @@ export function ArcadeMemoryPairsProvider({ children }: { children: ReactNode })
 
   // Action creators - send moves to arcade session
   const startGame = useCallback(() => {
+    // Must have at least one active player
+    if (activePlayers.length === 0) {
+      console.error('[ArcadeMemoryPairs] Cannot start game without active players')
+      return
+    }
+
     const cards = generateGameCards(state.gameType, state.difficulty)
+    // Use first active player as playerId for START_GAME move
+    const firstPlayer = activePlayers[0]
     sendMove({
       type: 'START_GAME',
+      playerId: firstPlayer,
       data: {
         cards,
         activePlayers
@@ -176,18 +186,43 @@ export function ArcadeMemoryPairsProvider({ children }: { children: ReactNode })
   }, [state.gameType, state.difficulty, activePlayers, sendMove])
 
   const flipCard = useCallback((cardId: string) => {
-    if (!canFlipCard(cardId)) return
-    sendMove({
-      type: 'FLIP_CARD',
-      data: { cardId }
+    console.log('[Client] flipCard called:', {
+      cardId,
+      viewerId,
+      currentPlayer: state.currentPlayer,
+      activePlayers: state.activePlayers,
+      gamePhase: state.gamePhase,
+      canFlip: canFlipCard(cardId)
     })
-  }, [canFlipCard, sendMove])
+
+    if (!canFlipCard(cardId)) {
+      console.log('[Client] Cannot flip card - canFlipCard returned false')
+      return
+    }
+
+    const move = {
+      type: 'FLIP_CARD' as const,
+      playerId: state.currentPlayer, // Use the current player ID from game state (database player ID)
+      data: { cardId }
+    }
+    console.log('[Client] Sending FLIP_CARD move via sendMove:', move)
+    sendMove(move)
+  }, [canFlipCard, sendMove, viewerId, state.currentPlayer, state.activePlayers, state.gamePhase])
 
   const resetGame = useCallback(() => {
+    // Must have at least one active player
+    if (activePlayers.length === 0) {
+      console.error('[ArcadeMemoryPairs] Cannot reset game without active players')
+      return
+    }
+
     // Delete current session and start a new game
     const cards = generateGameCards(state.gameType, state.difficulty)
+    // Use first active player as playerId for START_GAME move
+    const firstPlayer = activePlayers[0]
     sendMove({
       type: 'START_GAME',
+      playerId: firstPlayer,
       data: {
         cards,
         activePlayers