chore(release): 3.15.2 [skip ci]

## [3.15.2](https://github.com/antialias/soroban-abacus-flashcards/compare/v3.15.1...v3.15.2) (2025-10-15)

### Bug Fixes

* **memory-quiz:** prevent duplicate card processing from optimistic updates ([51676fc](51676fc15f))

CHANGELOG.md

@@ -1,3 +1,37 @@
+## [3.15.2](https://github.com/antialias/soroban-abacus-flashcards/compare/v3.15.1...v3.15.2) (2025-10-15)
+
+
+### Bug Fixes
+
+* **memory-quiz:** prevent duplicate card processing from optimistic updates ([51676fc](https://github.com/antialias/soroban-abacus-flashcards/commit/51676fc15f5bc15cdb43393d3e66f7c5a0667868))
+
+## [3.15.1](https://github.com/antialias/soroban-abacus-flashcards/compare/v3.15.0...v3.15.1) (2025-10-15)
+
+
+### Bug Fixes
+
+* **memory-quiz:** synchronize card display across all players in multiplayer ([472f201](https://github.com/antialias/soroban-abacus-flashcards/commit/472f201088d82f92030273fadaf8a8e488820d6c))
+
+## [3.15.0](https://github.com/antialias/soroban-abacus-flashcards/compare/v3.14.4...v3.15.0) (2025-10-15)
+
+
+### Features
+
+* **memory-quiz:** add multiplayer support with redesigned scoreboards ([1cf4469](https://github.com/antialias/soroban-abacus-flashcards/commit/1cf44696c26473ce4ab2fc2039ff42f08c20edb6))
+* **memory-quiz:** show player emojis on cards to indicate who found them ([05bd11a](https://github.com/antialias/soroban-abacus-flashcards/commit/05bd11a133706c9ed8c09c744da7ca8955fa979a))
+
+
+### Bug Fixes
+
+* **arcade:** add defensive checks and update test fixtures ([a93d981](https://github.com/antialias/soroban-abacus-flashcards/commit/a93d981d1ab3abed019b28cebe87525191313cc7))
+
+## [3.14.4](https://github.com/antialias/soroban-abacus-flashcards/compare/v3.14.3...v3.14.4) (2025-10-15)
+
+
+### Bug Fixes
+
+* **memory-quiz:** prevent input lag during rapid typing in room mode ([b45139b](https://github.com/antialias/soroban-abacus-flashcards/commit/b45139b588d0ab6df4d6c1003c1b65b634e2b041))
+
 ## [3.14.3](https://github.com/antialias/soroban-abacus-flashcards/compare/v3.14.2...v3.14.3) (2025-10-15)
 
 

apps/web/.claude/settings.local.json

@@ -69,7 +69,8 @@
       "Bash(git reset:*)",
       "Bash(lsof:*)",
       "Bash(killall:*)",
-      "Bash(echo:*)"
+      "Bash(echo:*)",
+      "Bash(git restore:*)"
     ],
     "deny": [],
     "ask": []

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

@@ -90,16 +90,19 @@ function applyMoveOptimistically(state: MemoryPairsState, move: GameMove): Memor
 
     case 'FLIP_CARD': {
       // Optimistically flip the card
-      const card = state.gameCards.find((c) => c.id === move.data.cardId)
+      // Defensive check: ensure arrays exist
+      const gameCards = state.gameCards || []
+      const flippedCards = state.flippedCards || []
+
+      const card = gameCards.find((c) => c.id === move.data.cardId)
       if (!card) return state
 
-      const newFlippedCards = [...state.flippedCards, card]
+      const newFlippedCards = [...flippedCards, card]
 
       return {
         ...state,
         flippedCards: newFlippedCards,
-        currentMoveStartTime:
-          state.flippedCards.length === 0 ? Date.now() : state.currentMoveStartTime,
+        currentMoveStartTime: flippedCards.length === 0 ? Date.now() : state.currentMoveStartTime,
         isProcessingMove: newFlippedCards.length === 2, // Processing if 2 cards flipped
         showMismatchFeedback: false,
       }
@@ -260,35 +263,51 @@ export function RoomMemoryPairsProvider({ children }: { children: ReactNode }) {
     applyMove: applyMoveOptimistically,
   })
 
+  // Detect state corruption/mismatch (e.g., game type mismatch between sessions)
+  const hasStateCorruption =
+    !state.gameCards || !state.flippedCards || !Array.isArray(state.gameCards)
+
   // Handle mismatch feedback timeout
   useEffect(() => {
-    if (state.showMismatchFeedback && state.flippedCards.length === 2) {
+    // Defensive check: ensure flippedCards exists
+    if (state.showMismatchFeedback && state.flippedCards?.length === 2) {
       // After 1.5 seconds, send CLEAR_MISMATCH
       // Server will validate that cards are still in mismatch state before clearing
       const timeout = setTimeout(() => {
         sendMove({
           type: 'CLEAR_MISMATCH',
           playerId: state.currentPlayer,
+          userId: viewerId || '',
           data: {},
         })
       }, 1500)
 
       return () => clearTimeout(timeout)
     }
-  }, [state.showMismatchFeedback, state.flippedCards.length, sendMove, state.currentPlayer])
+  }, [
+    state.showMismatchFeedback,
+    state.flippedCards?.length,
+    sendMove,
+    state.currentPlayer,
+    viewerId,
+  ])
 
   // Computed values
   const isGameActive = state.gamePhase === 'playing'
 
   const canFlipCard = useCallback(
     (cardId: string): boolean => {
+      // Defensive check: ensure required state exists
+      const flippedCards = state.flippedCards || []
+      const gameCards = state.gameCards || []
+
       console.log('[RoomProvider][canFlipCard] Checking card:', {
         cardId,
         isGameActive,
         isProcessingMove: state.isProcessingMove,
         currentPlayer: state.currentPlayer,
         hasRoomData: !!roomData,
-        flippedCardsCount: state.flippedCards.length,
+        flippedCardsCount: flippedCards.length,
       })
 
       if (!isGameActive || state.isProcessingMove) {
@@ -296,20 +315,20 @@ export function RoomMemoryPairsProvider({ children }: { children: ReactNode }) {
         return false
       }
 
-      const card = state.gameCards.find((c) => c.id === cardId)
+      const card = gameCards.find((c) => c.id === cardId)
       if (!card || card.matched) {
         console.log('[RoomProvider][canFlipCard] Blocked: card not found or already matched')
         return false
       }
 
       // Can't flip if already flipped
-      if (state.flippedCards.some((c) => c.id === cardId)) {
+      if (flippedCards.some((c) => c.id === cardId)) {
         console.log('[RoomProvider][canFlipCard] Blocked: card already flipped')
         return false
       }
 
       // Can't flip more than 2 cards
-      if (state.flippedCards.length >= 2) {
+      if (flippedCards.length >= 2) {
         console.log('[RoomProvider][canFlipCard] Blocked: 2 cards already flipped')
         return false
       }
@@ -414,13 +433,14 @@ export function RoomMemoryPairsProvider({ children }: { children: ReactNode }) {
     sendMove({
       type: 'START_GAME',
       playerId: firstPlayer,
+      userId: viewerId || '',
       data: {
         cards,
         activePlayers,
         playerMetadata,
       },
     })
-  }, [state.gameType, state.difficulty, activePlayers, buildPlayerMetadata, sendMove])
+  }, [state.gameType, state.difficulty, activePlayers, buildPlayerMetadata, sendMove, viewerId])
 
   const flipCard = useCallback(
     (cardId: string) => {
@@ -441,6 +461,7 @@ export function RoomMemoryPairsProvider({ children }: { children: ReactNode }) {
       const move = {
         type: 'FLIP_CARD' as const,
         playerId: state.currentPlayer, // Use the current player ID from game state (database player ID)
+        userId: viewerId || '',
         data: { cardId },
       }
       console.log('[RoomProvider] Sending FLIP_CARD move via sendMove:', move)
@@ -466,13 +487,14 @@ export function RoomMemoryPairsProvider({ children }: { children: ReactNode }) {
     sendMove({
       type: 'START_GAME',
       playerId: firstPlayer,
+      userId: viewerId || '',
       data: {
         cards,
         activePlayers,
         playerMetadata,
       },
     })
-  }, [state.gameType, state.difficulty, activePlayers, buildPlayerMetadata, sendMove])
+  }, [state.gameType, state.difficulty, activePlayers, buildPlayerMetadata, sendMove, viewerId])
 
   const setGameType = useCallback(
     (gameType: typeof state.gameType) => {
@@ -481,10 +503,11 @@ export function RoomMemoryPairsProvider({ children }: { children: ReactNode }) {
       sendMove({
         type: 'SET_CONFIG',
         playerId,
+        userId: viewerId || '',
         data: { field: 'gameType', value: gameType },
       })
     },
-    [activePlayers, sendMove]
+    [activePlayers, sendMove, viewerId]
   )
 
   const setDifficulty = useCallback(
@@ -493,10 +516,11 @@ export function RoomMemoryPairsProvider({ children }: { children: ReactNode }) {
       sendMove({
         type: 'SET_CONFIG',
         playerId,
+        userId: viewerId || '',
         data: { field: 'difficulty', value: difficulty },
       })
     },
-    [activePlayers, sendMove]
+    [activePlayers, sendMove, viewerId]
   )
 
   const setTurnTimer = useCallback(
@@ -505,10 +529,11 @@ export function RoomMemoryPairsProvider({ children }: { children: ReactNode }) {
       sendMove({
         type: 'SET_CONFIG',
         playerId,
+        userId: viewerId || '',
         data: { field: 'turnTimer', value: turnTimer },
       })
     },
-    [activePlayers, sendMove]
+    [activePlayers, sendMove, viewerId]
   )
 
   const goToSetup = useCallback(() => {
@@ -517,9 +542,10 @@ export function RoomMemoryPairsProvider({ children }: { children: ReactNode }) {
     sendMove({
       type: 'GO_TO_SETUP',
       playerId,
+      userId: viewerId || '',
       data: {},
     })
-  }, [activePlayers, state.currentPlayer, sendMove])
+  }, [activePlayers, state.currentPlayer, sendMove, viewerId])
 
   const resumeGame = useCallback(() => {
     // PAUSE/RESUME: Resume paused game if config unchanged
@@ -532,9 +558,10 @@ export function RoomMemoryPairsProvider({ children }: { children: ReactNode }) {
     sendMove({
       type: 'RESUME_GAME',
       playerId,
+      userId: viewerId || '',
       data: {},
     })
-  }, [canResumeGame, activePlayers, state.currentPlayer, sendMove])
+  }, [canResumeGame, activePlayers, state.currentPlayer, sendMove, viewerId])
 
   const hoverCard = useCallback(
     (cardId: string | null) => {
@@ -546,10 +573,11 @@ export function RoomMemoryPairsProvider({ children }: { children: ReactNode }) {
       sendMove({
         type: 'HOVER_CARD',
         playerId,
+        userId: viewerId || '',
         data: { cardId },
       })
     },
-    [state.currentPlayer, activePlayers, sendMove]
+    [state.currentPlayer, activePlayers, sendMove, viewerId]
   )
 
   // NO MORE effectiveState merging! Just use session state directly with gameMode added
@@ -557,6 +585,100 @@ export function RoomMemoryPairsProvider({ children }: { children: ReactNode }) {
     gameMode: GameMode
   }
 
+  // If state is corrupted, show error message instead of crashing
+  if (hasStateCorruption) {
+    return (
+      <div
+        style={{
+          display: 'flex',
+          flexDirection: 'column',
+          alignItems: 'center',
+          justifyContent: 'center',
+          padding: '40px',
+          textAlign: 'center',
+          minHeight: '400px',
+        }}
+      >
+        <div
+          style={{
+            fontSize: '48px',
+            marginBottom: '20px',
+          }}
+        >
+          ⚠️
+        </div>
+        <h2
+          style={{
+            fontSize: '24px',
+            fontWeight: 'bold',
+            marginBottom: '12px',
+            color: '#dc2626',
+          }}
+        >
+          Game State Mismatch
+        </h2>
+        <p
+          style={{
+            fontSize: '16px',
+            color: '#6b7280',
+            marginBottom: '24px',
+            maxWidth: '500px',
+          }}
+        >
+          There's a mismatch between game types in this room. This usually happens when room members
+          are playing different games.
+        </p>
+        <div
+          style={{
+            background: '#f9fafb',
+            border: '1px solid #e5e7eb',
+            borderRadius: '8px',
+            padding: '16px',
+            marginBottom: '24px',
+            maxWidth: '500px',
+          }}
+        >
+          <p
+            style={{
+              fontSize: '14px',
+              fontWeight: '600',
+              marginBottom: '8px',
+            }}
+          >
+            To fix this:
+          </p>
+          <ol
+            style={{
+              fontSize: '14px',
+              textAlign: 'left',
+              paddingLeft: '20px',
+              lineHeight: '1.6',
+            }}
+          >
+            <li>Make sure all room members are on the same game page</li>
+            <li>Try refreshing the page</li>
+            <li>If the issue persists, leave and rejoin the room</li>
+          </ol>
+        </div>
+        <button
+          onClick={() => window.location.reload()}
+          style={{
+            padding: '10px 20px',
+            background: '#3b82f6',
+            color: 'white',
+            border: 'none',
+            borderRadius: '6px',
+            fontSize: '14px',
+            fontWeight: '600',
+            cursor: 'pointer',
+          }}
+        >
+          Refresh Page
+        </button>
+      </div>
+    )
+  }
+
   const contextValue: MemoryPairsContextValue = {
     state: effectiveState,
     dispatch: () => {

apps/web/src/app/arcade/memory-quiz/components/DisplayPhase.tsx

@@ -12,13 +12,18 @@ function calculateMaxColumns(numbers: number[]): number {
 }
 
 export function DisplayPhase() {
-  const { state, nextCard, showInputPhase, resetGame } = useMemoryQuiz()
+  const { state, nextCard, showInputPhase, resetGame, isRoomCreator } = useMemoryQuiz()
   const [currentCard, setCurrentCard] = useState<QuizCard | null>(null)
   const [isTransitioning, setIsTransitioning] = useState(false)
   const isDisplayPhaseActive = state.currentCardIndex < state.quizCards.length
   const isProcessingRef = useRef(false)
+  const lastProcessedIndexRef = useRef(-1)
   const appConfig = useAbacusConfig()
 
+  // In multiplayer room mode, only the room creator controls card timing
+  // In local mode (isRoomCreator === undefined), allow timing control
+  const shouldControlTiming = isRoomCreator === undefined || isRoomCreator === true
+
   // Calculate maximum columns needed for this quiz set
   const maxColumns = useMemo(() => {
     const allNumbers = state.quizCards.map((card) => card.number)
@@ -34,21 +39,42 @@ export function DisplayPhase() {
   const progressPercentage = (state.currentCardIndex / state.quizCards.length) * 100
 
   useEffect(() => {
+    // Prevent processing the same card index multiple times
+    // This prevents race conditions from optimistic updates
+    if (state.currentCardIndex === lastProcessedIndexRef.current) {
+      console.log(
+        `DisplayPhase: Skipping duplicate processing of index ${state.currentCardIndex} (lastProcessed: ${lastProcessedIndexRef.current})`
+      )
+      return
+    }
+
     if (state.currentCardIndex >= state.quizCards.length) {
-      showInputPhase?.()
+      // Only the room creator (or local mode) triggers phase transitions
+      if (shouldControlTiming) {
+        console.log(
+          `DisplayPhase: All cards shown (${state.quizCards.length}), transitioning to input phase`
+        )
+        showInputPhase?.()
+      }
       return
     }
 
     // Prevent multiple concurrent executions
     if (isProcessingRef.current) {
+      console.log(
+        `DisplayPhase: Already processing, skipping (index: ${state.currentCardIndex}, lastProcessed: ${lastProcessedIndexRef.current})`
+      )
       return
     }
 
+    // Mark this index as being processed
+    lastProcessedIndexRef.current = state.currentCardIndex
+
     const showNextCard = async () => {
       isProcessingRef.current = true
       const card = state.quizCards[state.currentCardIndex]
       console.log(
-        `DisplayPhase: Showing card ${state.currentCardIndex + 1}/${state.quizCards.length}, number: ${card.number}`
+        `DisplayPhase: Showing card ${state.currentCardIndex + 1}/${state.quizCards.length}, number: ${card.number} (isRoomCreator: ${isRoomCreator}, shouldControlTiming: ${shouldControlTiming})`
       )
 
       // Calculate adaptive timing based on display speed
@@ -67,15 +93,26 @@ export function DisplayPhase() {
         `DisplayPhase: Card ${state.currentCardIndex + 1} now visible (flash: ${flashDuration}ms, pause: ${transitionPause}ms)`
       )
 
-      // Display card for specified time with adaptive transition pause
-      await new Promise((resolve) => setTimeout(resolve, displayTimeMs - transitionPause))
+      // Only the room creator (or local mode) controls the timing
+      if (shouldControlTiming) {
+        // Display card for specified time with adaptive transition pause
+        await new Promise((resolve) => setTimeout(resolve, displayTimeMs - transitionPause))
 
-      // Don't hide the abacus - just advance to next card for smooth transition
-      console.log(`DisplayPhase: Card ${state.currentCardIndex + 1} transitioning to next`)
-      await new Promise((resolve) => setTimeout(resolve, transitionPause)) // Adaptive pause for visual transition
+        // Don't hide the abacus - just advance to next card for smooth transition
+        console.log(
+          `DisplayPhase: Card ${state.currentCardIndex + 1} transitioning to next (controlled by ${isRoomCreator === undefined ? 'local mode' : 'room creator'})`
+        )
+        await new Promise((resolve) => setTimeout(resolve, transitionPause)) // Adaptive pause for visual transition
 
-      isProcessingRef.current = false
-      nextCard?.()
+        isProcessingRef.current = false
+        nextCard?.()
+      } else {
+        // Non-creator players just display the card, don't control timing
+        console.log(
+          `DisplayPhase: Non-creator player displaying card ${state.currentCardIndex + 1}, waiting for creator to advance`
+        )
+        isProcessingRef.current = false
+      }
     }
 
     showNextCard()
@@ -85,7 +122,8 @@ export function DisplayPhase() {
     state.quizCards.length,
     nextCard,
     showInputPhase,
-    state.quizCards[state.currentCardIndex],
+    shouldControlTiming,
+    isRoomCreator,
   ])
 
   return (

apps/web/src/app/arcade/memory-quiz/components/InputPhase.tsx

@@ -1,11 +1,10 @@
-import { useCallback, useEffect, useRef, useState } from 'react'
+import { useCallback, useEffect, useState } from 'react'
 import { isPrefix } from '@/lib/memory-quiz-utils'
 import { useMemoryQuiz } from '../context/MemoryQuizContext'
 import { CardGrid } from './CardGrid'
 
 export function InputPhase() {
   const { state, dispatch, acceptNumber, rejectNumber, setInput, showResults } = useMemoryQuiz()
-  const _containerRef = useRef<HTMLDivElement>(null)
   const [displayFeedback, setDisplayFeedback] = useState<'neutral' | 'correct' | 'incorrect'>(
     'neutral'
   )
@@ -107,7 +106,7 @@ export function InputPhase() {
   const acceptCorrectNumber = useCallback(
     (number: number) => {
       acceptNumber?.(number)
-      setInput?.('')
+      // setInput('') is called inside acceptNumber action creator
       setDisplayFeedback('correct')
 
       setTimeout(() => setDisplayFeedback('neutral'), 500)
@@ -117,7 +116,7 @@ export function InputPhase() {
         setTimeout(() => showResults?.(), 1000)
       }
     },
-    [acceptNumber, setInput, showResults, state.foundNumbers.length, state.correctAnswers.length]
+    [acceptNumber, showResults, state.foundNumbers.length, state.correctAnswers.length]
   )
 
   const handleIncorrectGuess = useCallback(() => {
@@ -131,7 +130,7 @@ export function InputPhase() {
     }
 
     rejectNumber?.()
-    setInput?.('')
+    // setInput('') is called inside rejectNumber action creator
     setDisplayFeedback('incorrect')
 
     setTimeout(() => setDisplayFeedback('neutral'), 500)
@@ -140,7 +139,7 @@ export function InputPhase() {
     if (state.guessesRemaining - 1 === 0) {
       setTimeout(() => showResults?.(), 1000)
     }
-  }, [dispatch, rejectNumber, setInput, showResults, state.guessesRemaining, state.currentInput])
+  }, [state.currentInput, dispatch, rejectNumber, showResults, state.guessesRemaining])
 
   // Simple keyboard event handlers that will be defined after callbacks
   const handleKeyboardInput = useCallback(
@@ -150,6 +149,7 @@ export function InputPhase() {
         // Only handle if input phase is active and guesses remain
         if (state.guessesRemaining === 0) return
 
+        // Update input with new key
         const newInput = state.currentInput + key
         setInput?.(newInput)
 
@@ -369,6 +369,172 @@ export function InputPhase() {
         </div>
       </div>
 
+      {/* Live Scoreboard - Competitive Mode Only */}
+      {state.playMode === 'competitive' &&
+        state.activePlayers &&
+        state.activePlayers.length > 1 && (
+          <div
+            style={{
+              marginBottom: '16px',
+              padding: '12px',
+              background: 'linear-gradient(135deg, #fef3c7 0%, #fde68a 100%)',
+              borderRadius: '8px',
+              border: '2px solid #f59e0b',
+            }}
+          >
+            <div
+              style={{
+                fontSize: '12px',
+                fontWeight: 'bold',
+                color: '#92400e',
+                marginBottom: '8px',
+                textAlign: 'center',
+              }}
+            >
+              🏆 LIVE SCOREBOARD
+            </div>
+            <div
+              style={{
+                display: 'flex',
+                flexDirection: 'column',
+                gap: '6px',
+              }}
+            >
+              {(() => {
+                // Group players by userId
+                const userTeams = new Map<
+                  string,
+                  { userId: string; players: any[]; score: { correct: number; incorrect: number } }
+                >()
+
+                console.log('📊 [InputPhase] Building scoreboard:', {
+                  activePlayers: state.activePlayers,
+                  playerMetadata: state.playerMetadata,
+                  playerScores: state.playerScores,
+                })
+
+                for (const playerId of state.activePlayers) {
+                  const metadata = state.playerMetadata?.[playerId]
+                  const userId = metadata?.userId
+                  console.log('📊 [InputPhase] Processing player for scoreboard:', {
+                    playerId,
+                    metadata,
+                    userId,
+                  })
+                  if (!userId) continue
+
+                  if (!userTeams.has(userId)) {
+                    userTeams.set(userId, {
+                      userId,
+                      players: [],
+                      score: state.playerScores?.[userId] || { correct: 0, incorrect: 0 },
+                    })
+                  }
+                  userTeams.get(userId)!.players.push(metadata)
+                }
+
+                console.log('📊 [InputPhase] UserTeams created:', {
+                  count: userTeams.size,
+                  teams: Array.from(userTeams.entries()),
+                })
+
+                // Sort teams by score
+                return Array.from(userTeams.values())
+                  .sort((a, b) => {
+                    const aScore = a.score.correct - a.score.incorrect * 0.5
+                    const bScore = b.score.correct - b.score.incorrect * 0.5
+                    return bScore - aScore
+                  })
+                  .map((team, index) => {
+                    const netScore = team.score.correct - team.score.incorrect * 0.5
+                    return (
+                      <div
+                        key={team.userId}
+                        style={{
+                          padding: '10px 12px',
+                          background: index === 0 ? '#fef3c7' : 'white',
+                          borderRadius: '8px',
+                          border: index === 0 ? '2px solid #f59e0b' : '1px solid #e5e7eb',
+                        }}
+                      >
+                        {/* Team header with rank and stats */}
+                        <div
+                          style={{
+                            display: 'flex',
+                            alignItems: 'center',
+                            justifyContent: 'space-between',
+                            marginBottom: '8px',
+                          }}
+                        >
+                          <div style={{ display: 'flex', alignItems: 'center', gap: '8px' }}>
+                            <span style={{ fontSize: '18px' }}>
+                              {index === 0 ? '👑' : `${index + 1}.`}
+                            </span>
+                            <span
+                              style={{
+                                fontWeight: 'bold',
+                                fontSize: '16px',
+                                color: '#1f2937',
+                              }}
+                            >
+                              Score: {netScore.toFixed(1)}
+                            </span>
+                          </div>
+                          <div
+                            style={{
+                              display: 'flex',
+                              alignItems: 'center',
+                              gap: '10px',
+                              fontSize: '14px',
+                            }}
+                          >
+                            <span style={{ color: '#10b981', fontWeight: 'bold' }}>
+                              ✓{team.score.correct}
+                            </span>
+                            <span style={{ color: '#ef4444', fontWeight: 'bold' }}>
+                              ✗{team.score.incorrect}
+                            </span>
+                          </div>
+                        </div>
+                        {/* Players list */}
+                        <div
+                          style={{
+                            display: 'flex',
+                            flexDirection: 'column',
+                            gap: '4px',
+                            paddingLeft: '26px',
+                          }}
+                        >
+                          {team.players.map((player, i) => (
+                            <div
+                              key={i}
+                              style={{
+                                display: 'flex',
+                                alignItems: 'center',
+                                gap: '6px',
+                                fontSize: '13px',
+                              }}
+                            >
+                              <span style={{ fontSize: '16px' }}>{player?.emoji || '🎮'}</span>
+                              <span
+                                style={{
+                                  color: '#1f2937',
+                                  fontWeight: '500',
+                                }}
+                              >
+                                {player?.name || `Player ${i + 1}`}
+                              </span>
+                            </div>
+                          ))}
+                        </div>
+                      </div>
+                    )
+                  })
+              })()}
+            </div>
+          </div>
+        )}
+
       <div
         style={{
           position: 'relative',

apps/web/src/app/arcade/memory-quiz/components/MemoryQuizGame.tsx

@@ -80,78 +80,78 @@ export function MemoryQuizGame() {
     >
       <style dangerouslySetInnerHTML={{ __html: globalAnimations }} />
 
+      <div
+        style={{
+          flex: 1,
+          display: 'flex',
+          flexDirection: 'column',
+          overflow: 'auto',
+          padding: '20px 8px',
+          minHeight: '100vh',
+          background: 'linear-gradient(135deg, #f8fafc, #e2e8f0)',
+        }}
+      >
         <div
           style={{
+            maxWidth: '100%',
+            margin: '0 auto',
             flex: 1,
             display: 'flex',
             flexDirection: 'column',
-            overflow: 'auto',
-            padding: '20px 8px',
-            minHeight: '100vh',
-            background: 'linear-gradient(135deg, #f8fafc, #e2e8f0)',
           }}
         >
           <div
-            style={{
-              maxWidth: '100%',
-              margin: '0 auto',
+            className={css({
+              textAlign: 'center',
+              mb: '4',
+              flexShrink: 0,
+            })}
+          >
+            <Link
+              href="/arcade"
+              className={css({
+                display: 'inline-flex',
+                alignItems: 'center',
+                color: 'gray.600',
+                textDecoration: 'none',
+                mb: '4',
+                _hover: { color: 'gray.800' },
+              })}
+            >
+              ← Back to Champion Arena
+            </Link>
+          </div>
+
+          <div
+            className={css({
+              bg: 'white',
+              rounded: 'xl',
+              shadow: 'xl',
+              overflow: 'hidden',
+              border: '1px solid',
+              borderColor: 'gray.200',
               flex: 1,
               display: 'flex',
               flexDirection: 'column',
-            }}
+              maxHeight: '100%',
+            })}
           >
             <div
               className={css({
-                textAlign: 'center',
-                mb: '4',
-                flexShrink: 0,
-              })}
-            >
-              <Link
-                href="/arcade"
-                className={css({
-                  display: 'inline-flex',
-                  alignItems: 'center',
-                  color: 'gray.600',
-                  textDecoration: 'none',
-                  mb: '4',
-                  _hover: { color: 'gray.800' },
-                })}
-              >
-                ← Back to Champion Arena
-              </Link>
-            </div>
-
-            <div
-              className={css({
-                bg: 'white',
-                rounded: 'xl',
-                shadow: 'xl',
-                overflow: 'hidden',
-                border: '1px solid',
-                borderColor: 'gray.200',
                 flex: 1,
                 display: 'flex',
                 flexDirection: 'column',
-                maxHeight: '100%',
+                overflow: 'auto',
               })}
             >
-              <div
-                className={css({
-                  flex: 1,
-                  display: 'flex',
-                  flexDirection: 'column',
-                  overflow: 'auto',
-                })}
-              >
-                {state.gamePhase === 'setup' && <SetupPhase />}
-                {state.gamePhase === 'display' && <DisplayPhase />}
-                {state.gamePhase === 'input' && <InputPhase key="input-phase" />}
-                {state.gamePhase === 'results' && <ResultsPhase />}
-              </div>
+              {state.gamePhase === 'setup' && <SetupPhase />}
+              {state.gamePhase === 'display' && <DisplayPhase />}
+              {state.gamePhase === 'input' && <InputPhase key="input-phase" />}
+              {state.gamePhase === 'results' && <ResultsPhase />}
             </div>
           </div>
         </div>
+      </div>
     </PageWithNav>
   )
 }

apps/web/src/app/arcade/memory-quiz/components/ResultsCardGrid.tsx

@@ -147,26 +147,61 @@ export function ResultsCardGrid({ state }: ResultsCardGridProps) {
                     </div>
                   </div>
 
-                  {/* Right/Wrong indicator overlay */}
+                  {/* Player indicator overlay */}
                   <div
                     style={{
                       position: 'absolute',
                       top: '4px',
                       right: '4px',
-                      width: '20px',
-                      height: '20px',
-                      borderRadius: '50%',
+                      minWidth: wasFound ? '24px' : '20px',
+                      minHeight: '20px',
+                      maxHeight: '48px',
+                      borderRadius: wasFound ? '8px' : '50%',
                       background: wasFound ? '#10b981' : '#ef4444',
                       color: 'white',
                       display: 'flex',
+                      flexDirection: 'column',
                       alignItems: 'center',
                       justifyContent: 'center',
-                      fontSize: '12px',
+                      fontSize: wasFound ? '14px' : '12px',
                       fontWeight: 'bold',
                       boxShadow: '0 1px 2px rgba(0, 0, 0, 0.2)',
+                      padding: wasFound ? '2px' : '0',
+                      gap: '1px',
+                      overflow: 'hidden',
                     }}
                   >
-                    {wasFound ? '✓' : '✗'}
+                    {wasFound
+                      ? (() => {
+                          // Get the userId who found this number
+                          const foundByUserId = state.numberFoundBy?.[card.number]
+                          if (!foundByUserId) return '✓'
+
+                          // Get all players on that team
+                          const teamPlayers = state.activePlayers
+                            ?.filter((playerId) => {
+                              const metadata = state.playerMetadata?.[playerId]
+                              return metadata?.userId === foundByUserId
+                            })
+                            .map((playerId) => state.playerMetadata?.[playerId])
+                            .filter(Boolean)
+
+                          if (!teamPlayers || teamPlayers.length === 0) return '✓'
+
+                          // Display emojis (stacked vertically if multiple)
+                          return teamPlayers.map((player, idx) => (
+                            <span
+                              key={idx}
+                              style={{
+                                lineHeight: '1',
+                                fontSize: '14px',
+                              }}
+                            >
+                              {player?.emoji || '🎮'}
+                            </span>
+                          ))
+                        })()
+                      : '✗'}
                   </div>
 
                   {/* Number label overlay */}

apps/web/src/app/arcade/memory-quiz/components/ResultsPhase.tsx

@@ -131,6 +131,374 @@ export function ResultsPhase() {
         </div>
       </div>
 
+      {/* Multiplayer Leaderboard - Competitive Mode */}
+      {state.playMode === 'competitive' &&
+        state.activePlayers &&
+        state.activePlayers.length > 1 && (
+          <div
+            style={{
+              marginBottom: '16px',
+              padding: '16px',
+              background: 'linear-gradient(135deg, #fef3c7 0%, #fde68a 100%)',
+              borderRadius: '12px',
+              border: '2px solid #f59e0b',
+            }}
+          >
+            <div
+              style={{
+                fontSize: '16px',
+                fontWeight: 'bold',
+                color: '#92400e',
+                marginBottom: '12px',
+                textAlign: 'center',
+              }}
+            >
+              🏆 FINAL LEADERBOARD
+            </div>
+            <div
+              style={{
+                display: 'flex',
+                flexDirection: 'column',
+                gap: '8px',
+              }}
+            >
+              {(() => {
+                // Group players by userId
+                const userTeams = new Map<
+                  string,
+                  { userId: string; players: any[]; score: { correct: number; incorrect: number } }
+                >()
+
+                console.log('🏆 [ResultsPhase] Building leaderboard:', {
+                  activePlayers: state.activePlayers,
+                  playerMetadata: state.playerMetadata,
+                  playerScores: state.playerScores,
+                })
+
+                for (const playerId of state.activePlayers) {
+                  const metadata = state.playerMetadata?.[playerId]
+                  const userId = metadata?.userId
+                  console.log('🏆 [ResultsPhase] Processing player for leaderboard:', {
+                    playerId,
+                    metadata,
+                    userId,
+                  })
+                  if (!userId) continue
+
+                  if (!userTeams.has(userId)) {
+                    userTeams.set(userId, {
+                      userId,
+                      players: [],
+                      score: state.playerScores?.[userId] || { correct: 0, incorrect: 0 },
+                    })
+                  }
+                  userTeams.get(userId)!.players.push(metadata)
+                }
+
+                console.log('🏆 [ResultsPhase] UserTeams created:', {
+                  count: userTeams.size,
+                  teams: Array.from(userTeams.entries()),
+                })
+
+                // Sort teams by score
+                return Array.from(userTeams.values())
+                  .sort((a, b) => {
+                    const aScore = a.score.correct - a.score.incorrect * 0.5
+                    const bScore = b.score.correct - b.score.incorrect * 0.5
+                    return bScore - aScore
+                  })
+                  .map((team, index) => {
+                    const netScore = team.score.correct - team.score.incorrect * 0.5
+                    return (
+                      <div
+                        key={team.userId}
+                        style={{
+                          padding: '14px 16px',
+                          background:
+                            index === 0
+                              ? 'linear-gradient(135deg, #fef3c7 0%, #fde68a 50%)'
+                              : 'white',
+                          borderRadius: '10px',
+                          border: index === 0 ? '3px solid #f59e0b' : '1px solid #e5e7eb',
+                          boxShadow: index === 0 ? '0 4px 12px rgba(245, 158, 11, 0.3)' : 'none',
+                        }}
+                      >
+                        {/* Team header with rank and stats */}
+                        <div
+                          style={{
+                            display: 'flex',
+                            alignItems: 'center',
+                            justifyContent: 'space-between',
+                            marginBottom: '10px',
+                          }}
+                        >
+                          <div style={{ display: 'flex', alignItems: 'center', gap: '10px' }}>
+                            <span style={{ fontSize: '24px', minWidth: '32px' }}>
+                              {index === 0
+                                ? '🏆'
+                                : index === 1
+                                  ? '🥈'
+                                  : index === 2
+                                    ? '🥉'
+                                    : `${index + 1}.`}
+                            </span>
+                            <div style={{ display: 'flex', flexDirection: 'column' }}>
+                              <span
+                                style={{
+                                  fontWeight: 'bold',
+                                  fontSize: index === 0 ? '20px' : '18px',
+                                  color: index === 0 ? '#f59e0b' : '#1f2937',
+                                }}
+                              >
+                                {netScore.toFixed(1)}
+                              </span>
+                              {index === 0 && (
+                                <span
+                                  style={{
+                                    fontSize: '11px',
+                                    color: '#92400e',
+                                    fontWeight: 'bold',
+                                  }}
+                                >
+                                  CHAMPION
+                                </span>
+                              )}
+                            </div>
+                          </div>
+                          <div
+                            style={{
+                              display: 'flex',
+                              alignItems: 'center',
+                              gap: '12px',
+                            }}
+                          >
+                            <div
+                              style={{
+                                display: 'flex',
+                                flexDirection: 'column',
+                                alignItems: 'center',
+                              }}
+                            >
+                              <span
+                                style={{
+                                  color: '#10b981',
+                                  fontWeight: 'bold',
+                                  fontSize: '16px',
+                                }}
+                              >
+                                ✓{team.score.correct}
+                              </span>
+                              <span style={{ fontSize: '10px', color: '#6b7280' }}>correct</span>
+                            </div>
+                            <div
+                              style={{
+                                display: 'flex',
+                                flexDirection: 'column',
+                                alignItems: 'center',
+                              }}
+                            >
+                              <span
+                                style={{
+                                  color: '#ef4444',
+                                  fontWeight: 'bold',
+                                  fontSize: '16px',
+                                }}
+                              >
+                                ✗{team.score.incorrect}
+                              </span>
+                              <span style={{ fontSize: '10px', color: '#6b7280' }}>wrong</span>
+                            </div>
+                          </div>
+                        </div>
+                        {/* Players list */}
+                        <div
+                          style={{
+                            display: 'flex',
+                            flexDirection: 'column',
+                            gap: '6px',
+                            paddingLeft: '42px',
+                          }}
+                        >
+                          {team.players.map((player, i) => (
+                            <div
+                              key={i}
+                              style={{
+                                display: 'flex',
+                                alignItems: 'center',
+                                gap: '8px',
+                              }}
+                            >
+                              <span style={{ fontSize: '18px' }}>{player?.emoji || '🎮'}</span>
+                              <span
+                                style={{
+                                  color: '#1f2937',
+                                  fontWeight: '500',
+                                  fontSize: '14px',
+                                }}
+                              >
+                                {player?.name || `Player ${i + 1}`}
+                              </span>
+                            </div>
+                          ))}
+                        </div>
+                      </div>
+                    )
+                  })
+              })()}
+            </div>
+          </div>
+        )}
+
+      {/* Multiplayer Stats - Cooperative Mode */}
+      {state.playMode === 'cooperative' &&
+        state.activePlayers &&
+        state.activePlayers.length > 1 && (
+          <div
+            style={{
+              marginBottom: '16px',
+              padding: '16px',
+              background: 'linear-gradient(135deg, #dbeafe 0%, #bfdbfe 100%)',
+              borderRadius: '12px',
+              border: '2px solid #3b82f6',
+            }}
+          >
+            <div
+              style={{
+                fontSize: '16px',
+                fontWeight: 'bold',
+                color: '#1e3a8a',
+                marginBottom: '12px',
+                textAlign: 'center',
+              }}
+            >
+              🤝 TEAM CONTRIBUTIONS
+            </div>
+            <div
+              style={{
+                display: 'flex',
+                flexDirection: 'column',
+                gap: '8px',
+              }}
+            >
+              {(() => {
+                // Group players by userId
+                const userTeams = new Map<
+                  string,
+                  { userId: string; players: any[]; score: { correct: number; incorrect: 0 } }
+                >()
+
+                console.log('🤝 [ResultsPhase] Building team contributions:', {
+                  activePlayers: state.activePlayers,
+                  playerMetadata: state.playerMetadata,
+                  playerScores: state.playerScores,
+                })
+
+                for (const playerId of state.activePlayers) {
+                  const metadata = state.playerMetadata?.[playerId]
+                  const userId = metadata?.userId
+                  console.log('🤝 [ResultsPhase] Processing player for contributions:', {
+                    playerId,
+                    metadata,
+                    userId,
+                  })
+                  if (!userId) continue
+
+                  if (!userTeams.has(userId)) {
+                    userTeams.set(userId, {
+                      userId,
+                      players: [],
+                      score: state.playerScores?.[userId] || { correct: 0, incorrect: 0 },
+                    })
+                  }
+                  userTeams.get(userId)!.players.push(metadata)
+                }
+
+                console.log('🤝 [ResultsPhase] UserTeams created for contributions:', {
+                  count: userTeams.size,
+                  teams: Array.from(userTeams.entries()),
+                })
+
+                // Sort teams by correct answers
+                return Array.from(userTeams.values())
+                  .sort((a, b) => b.score.correct - a.score.correct)
+                  .map((team, index) => (
+                    <div
+                      key={team.userId}
+                      style={{
+                        padding: '12px 14px',
+                        background: 'white',
+                        borderRadius: '8px',
+                        border: '1px solid #e5e7eb',
+                      }}
+                    >
+                      {/* Team header with stats */}
+                      <div
+                        style={{
+                          display: 'flex',
+                          alignItems: 'center',
+                          justifyContent: 'space-between',
+                          marginBottom: '8px',
+                        }}
+                      >
+                        <div style={{ display: 'flex', alignItems: 'center', gap: '8px' }}>
+                          <span style={{ fontSize: '16px', fontWeight: '600', color: '#6b7280' }}>
+                            Team {index + 1}
+                          </span>
+                        </div>
+                        <div
+                          style={{
+                            display: 'flex',
+                            alignItems: 'center',
+                            gap: '10px',
+                            fontSize: '14px',
+                          }}
+                        >
+                          <span style={{ color: '#10b981', fontWeight: 'bold' }}>
+                            ✓ {team.score.correct}
+                          </span>
+                          <span style={{ color: '#ef4444', fontWeight: 'bold' }}>
+                            ✗ {team.score.incorrect}
+                          </span>
+                        </div>
+                      </div>
+                      {/* Players list */}
+                      <div
+                        style={{
+                          display: 'flex',
+                          flexDirection: 'column',
+                          gap: '4px',
+                          paddingLeft: '8px',
+                        }}
+                      >
+                        {team.players.map((player, i) => (
+                          <div
+                            key={i}
+                            style={{
+                              display: 'flex',
+                              alignItems: 'center',
+                              gap: '6px',
+                              fontSize: '13px',
+                            }}
+                          >
+                            <span style={{ fontSize: '18px' }}>{player?.emoji || '🎮'}</span>
+                            <span
+                              style={{
+                                color: '#1f2937',
+                                fontWeight: '500',
+                              }}
+                            >
+                              {player?.name || `Player ${i + 1}`}
+                            </span>
+                          </div>
+                        ))}
+                      </div>
+                    </div>
+                  ))
+              })()}
+            </div>
+          </div>
+        )}
+
       {/* Results card grid - reuse CardGrid but with all cards revealed and status indicators */}
       <div style={{ marginTop: '12px', flex: 1, overflow: 'auto' }}>
         <ResultsCardGrid state={state} />

apps/web/src/app/arcade/memory-quiz/components/SetupPhase.tsx

@@ -69,6 +69,10 @@ export function SetupPhase() {
     setConfig?.('selectedDifficulty', difficulty)
   }
 
+  const handlePlayModeSelect = (playMode: 'cooperative' | 'competitive') => {
+    setConfig?.('playMode', playMode)
+  }
+
   const handleStartQuiz = () => {
     const quizCards = generateQuizCards(
       state.selectedCount ?? 5,
@@ -150,6 +154,75 @@ export function SetupPhase() {
           </div>
         </div>
 
+        <div style={{ margin: '12px 0' }}>
+          <label
+            style={{
+              display: 'block',
+              fontWeight: 'bold',
+              marginBottom: '8px',
+              color: '#6b7280',
+              fontSize: '14px',
+            }}
+          >
+            Play Mode:
+          </label>
+          <div
+            style={{
+              display: 'grid',
+              gridTemplateColumns: 'repeat(2, 1fr)',
+              gap: '8px',
+              justifyContent: 'center',
+            }}
+          >
+            <button
+              key="cooperative"
+              type="button"
+              style={{
+                background: state.playMode === 'cooperative' ? '#10b981' : 'white',
+                color: state.playMode === 'cooperative' ? 'white' : '#1f2937',
+                border: '2px solid',
+                borderColor: state.playMode === 'cooperative' ? '#10b981' : '#d1d5db',
+                borderRadius: '8px',
+                padding: '8px 12px',
+                cursor: 'pointer',
+                textAlign: 'center',
+                display: 'flex',
+                flexDirection: 'column',
+                gap: '2px',
+                fontSize: '12px',
+              }}
+              onClick={() => handlePlayModeSelect('cooperative')}
+              title="Work together as a team to find all numbers"
+            >
+              <div style={{ fontWeight: 'bold', fontSize: '13px' }}>🤝 Cooperative</div>
+              <div style={{ fontSize: '10px', opacity: 0.8 }}>Work together</div>
+            </button>
+            <button
+              key="competitive"
+              type="button"
+              style={{
+                background: state.playMode === 'competitive' ? '#ef4444' : 'white',
+                color: state.playMode === 'competitive' ? 'white' : '#1f2937',
+                border: '2px solid',
+                borderColor: state.playMode === 'competitive' ? '#ef4444' : '#d1d5db',
+                borderRadius: '8px',
+                padding: '8px 12px',
+                cursor: 'pointer',
+                textAlign: 'center',
+                display: 'flex',
+                flexDirection: 'column',
+                gap: '2px',
+                fontSize: '12px',
+              }}
+              onClick={() => handlePlayModeSelect('competitive')}
+              title="Compete for the highest score"
+            >
+              <div style={{ fontWeight: 'bold', fontSize: '13px' }}>🏆 Competitive</div>
+              <div style={{ fontSize: '10px', opacity: 0.8 }}>Battle for score</div>
+            </button>
+          </div>
+        </div>
+
         <div style={{ margin: '12px 0' }}>
           <label
             style={{

apps/web/src/app/arcade/memory-quiz/context/MemoryQuizContext.tsx

@@ -10,6 +10,7 @@ export interface MemoryQuizContextValue {
 
   // Computed values
   isGameActive: boolean
+  isRoomCreator?: boolean // True if current user is room creator (controls timing in multiplayer)
 
   // Action creators (to be implemented by providers)
   // Local mode uses dispatch, room mode uses these action creators
@@ -25,7 +26,10 @@ export interface MemoryQuizContextValue {
   rejectNumber?: () => void
   setInput?: (input: string) => void
   showResults?: () => void
-  setConfig?: (field: 'selectedCount' | 'displayTime' | 'selectedDifficulty', value: any) => void
+  setConfig?: (
+    field: 'selectedCount' | 'displayTime' | 'selectedDifficulty' | 'playMode',
+    value: any
+  ) => void
 }
 
 // Create context

apps/web/src/app/arcade/memory-quiz/context/RoomMemoryQuizProvider.tsx

@@ -1,11 +1,17 @@
 'use client'
 
 import type { ReactNode } from 'react'
-import { useCallback, useEffect } from 'react'
+import { useCallback, useEffect, useState } from 'react'
+import { useGameMode } from '@/contexts/GameModeContext'
 import { useArcadeSession } from '@/hooks/useArcadeSession'
 import { useRoomData } from '@/hooks/useRoomData'
 import { useViewerId } from '@/hooks/useViewerId'
 import type { GameMove } from '@/lib/arcade/validation'
+import { TEAM_MOVE } from '@/lib/arcade/validation/types'
+import {
+  buildPlayerMetadata as buildPlayerMetadataUtil,
+  buildPlayerOwnershipFromRoomData,
+} from '@/lib/arcade/player-ownership.client'
 import { initialState } from '../reducer'
 import type { QuizCard, SorobanQuizState } from '../types'
 import { MemoryQuizContext, type MemoryQuizContextValue } from './MemoryQuizContext'
@@ -45,6 +51,39 @@ function applyMoveOptimistically(state: SorobanQuizState, move: GameMove): Sorob
 
       const cardCount = quizCards.length
 
+      // Initialize player scores for all active players (by userId, not playerId)
+      const activePlayers = move.data.activePlayers || []
+      const playerMetadata = move.data.playerMetadata || {}
+
+      console.log('🎯 [START_QUIZ] Initializing player scores:', {
+        activePlayers,
+        playerMetadata,
+      })
+
+      // Extract unique userIds from playerMetadata
+      const uniqueUserIds = new Set<string>()
+      for (const playerId of activePlayers) {
+        const metadata = playerMetadata[playerId]
+        console.log('🎯 [START_QUIZ] Processing player:', {
+          playerId,
+          metadata,
+          hasUserId: !!metadata?.userId,
+        })
+        if (metadata?.userId) {
+          uniqueUserIds.add(metadata.userId)
+        }
+      }
+
+      console.log('🎯 [START_QUIZ] Unique userIds found:', Array.from(uniqueUserIds))
+
+      // Initialize scores for each userId
+      const playerScores = Array.from(uniqueUserIds).reduce((acc: any, userId: string) => {
+        acc[userId] = { correct: 0, incorrect: 0 }
+        return acc
+      }, {})
+
+      console.log('🎯 [START_QUIZ] Initialized playerScores:', playerScores)
+
       return {
         ...state,
         quizCards,
@@ -57,6 +96,10 @@ function applyMoveOptimistically(state: SorobanQuizState, move: GameMove): Sorob
         currentInput: '',
         wrongGuessAnimations: [],
         prefixAcceptanceTimeout: null,
+        // Multiplayer state
+        activePlayers,
+        playerMetadata,
+        playerScores,
       }
     }
 
@@ -72,26 +115,80 @@ function applyMoveOptimistically(state: SorobanQuizState, move: GameMove): Sorob
         gamePhase: 'input',
       }
 
-    case 'ACCEPT_NUMBER':
+    case 'ACCEPT_NUMBER': {
+      // Track scores by userId (not playerId) since we can't determine which player typed
+      // Defensive check: ensure state properties exist
+      const playerScores = state.playerScores || {}
+      const foundNumbers = state.foundNumbers || []
+      const numberFoundBy = state.numberFoundBy || {}
+
+      console.log('✅ [ACCEPT_NUMBER] Before update:', {
+        moveUserId: move.userId,
+        currentPlayerScores: playerScores,
+        number: move.data.number,
+      })
+
+      const newPlayerScores = { ...playerScores }
+      const newNumberFoundBy = { ...numberFoundBy }
+
+      if (move.userId) {
+        const currentScore = newPlayerScores[move.userId] || { correct: 0, incorrect: 0 }
+        newPlayerScores[move.userId] = {
+          ...currentScore,
+          correct: currentScore.correct + 1,
+        }
+        // Track who found this number
+        newNumberFoundBy[move.data.number] = move.userId
+
+        console.log('✅ [ACCEPT_NUMBER] After update:', {
+          userId: move.userId,
+          newScore: newPlayerScores[move.userId],
+          allScores: newPlayerScores,
+          numberFoundBy: move.data.number,
+        })
+      } else {
+        console.warn('⚠️ [ACCEPT_NUMBER] No userId in move!')
+      }
       return {
         ...state,
-        foundNumbers: [...state.foundNumbers, move.data.number],
-        currentInput: '',
+        foundNumbers: [...foundNumbers, move.data.number],
+        playerScores: newPlayerScores,
+        numberFoundBy: newNumberFoundBy,
       }
+    }
 
-    case 'REJECT_NUMBER':
+    case 'REJECT_NUMBER': {
+      // Track scores by userId (not playerId) since we can't determine which player typed
+      // Defensive check: ensure state properties exist
+      const playerScores = state.playerScores || {}
+
+      console.log('❌ [REJECT_NUMBER] Before update:', {
+        moveUserId: move.userId,
+        currentPlayerScores: playerScores,
+      })
+
+      const newPlayerScores = { ...playerScores }
+      if (move.userId) {
+        const currentScore = newPlayerScores[move.userId] || { correct: 0, incorrect: 0 }
+        newPlayerScores[move.userId] = {
+          ...currentScore,
+          incorrect: currentScore.incorrect + 1,
+        }
+        console.log('❌ [REJECT_NUMBER] After update:', {
+          userId: move.userId,
+          newScore: newPlayerScores[move.userId],
+          allScores: newPlayerScores,
+        })
+      } else {
+        console.warn('⚠️ [REJECT_NUMBER] No userId in move!')
+      }
       return {
         ...state,
         guessesRemaining: state.guessesRemaining - 1,
         incorrectGuesses: state.incorrectGuesses + 1,
-        currentInput: '',
-      }
-
-    case 'SET_INPUT':
-      return {
-        ...state,
-        currentInput: move.data.input,
+        playerScores: newPlayerScores,
       }
+    }
 
     case 'SHOW_RESULTS':
       return {
@@ -117,7 +214,7 @@ function applyMoveOptimistically(state: SorobanQuizState, move: GameMove): Sorob
 
     case 'SET_CONFIG': {
       const { field, value } = move.data as {
-        field: 'selectedCount' | 'displayTime' | 'selectedDifficulty'
+        field: 'selectedCount' | 'displayTime' | 'selectedDifficulty' | 'playMode'
         value: any
       }
       return {
@@ -140,6 +237,14 @@ function applyMoveOptimistically(state: SorobanQuizState, move: GameMove): Sorob
 export function RoomMemoryQuizProvider({ children }: { children: ReactNode }) {
   const { data: viewerId } = useViewerId()
   const { roomData } = useRoomData()
+  const { activePlayers: activePlayerIds, players } = useGameMode()
+
+  // Get active player IDs as array
+  const activePlayers = Array.from(activePlayerIds)
+
+  // LOCAL-ONLY state for current input (not synced over network)
+  // This prevents sending a network request for every keystroke
+  const [localCurrentInput, setLocalCurrentInput] = useState('')
 
   // Arcade session integration WITH room sync
   const {
@@ -154,6 +259,13 @@ export function RoomMemoryQuizProvider({ children }: { children: ReactNode }) {
     applyMove: applyMoveOptimistically,
   })
 
+  // Clear local input when game phase changes or when game resets
+  useEffect(() => {
+    if (state.gamePhase !== 'input') {
+      setLocalCurrentInput('')
+    }
+  }, [state.gamePhase])
+
   // Cleanup timeouts on unmount
   useEffect(() => {
     return () => {
@@ -163,33 +275,71 @@ export function RoomMemoryQuizProvider({ children }: { children: ReactNode }) {
     }
   }, [state.prefixAcceptanceTimeout])
 
+  // Detect state corruption/mismatch (e.g., game type mismatch between sessions)
+  const hasStateCorruption =
+    !state.quizCards ||
+    !state.correctAnswers ||
+    !state.foundNumbers ||
+    !Array.isArray(state.quizCards)
+
   // Computed values
   const isGameActive = state.gamePhase === 'display' || state.gamePhase === 'input'
 
+  // Build player metadata from room data and player map
+  const buildPlayerMetadata = useCallback(() => {
+    console.log('🔍 [buildPlayerMetadata] Starting:', {
+      roomData: roomData?.id,
+      activePlayers,
+      viewerId,
+      playersMapSize: players.size,
+    })
+
+    const playerOwnership = buildPlayerOwnershipFromRoomData(roomData)
+    console.log('🔍 [buildPlayerMetadata] Player ownership:', playerOwnership)
+
+    const metadata = buildPlayerMetadataUtil(activePlayers, playerOwnership, players, viewerId)
+    console.log('🔍 [buildPlayerMetadata] Built metadata:', metadata)
+
+    return metadata
+  }, [activePlayers, players, roomData, viewerId])
+
   // Action creators - send moves to arcade session
-  // For single-player quiz, we use viewerId as playerId
   const startQuiz = useCallback(
     (quizCards: QuizCard[]) => {
       // Extract only serializable data (numbers) for server
       // React components can't be sent over Socket.IO
       const numbers = quizCards.map((card) => card.number)
 
+      // Build player metadata for multiplayer
+      const playerMetadata = buildPlayerMetadata()
+
+      console.log('🚀 [startQuiz] Sending START_QUIZ move:', {
+        viewerId,
+        activePlayers,
+        playerMetadata,
+        numbers,
+      })
+
       sendMove({
         type: 'START_QUIZ',
-        playerId: viewerId || '',
+        playerId: TEAM_MOVE, // Team move - all players act together
+        userId: viewerId || '', // User who initiated
         data: {
           numbers, // Send to server
           quizCards, // Keep for optimistic local update
+          activePlayers, // Send active players list
+          playerMetadata, // Send player display info
         },
       })
     },
-    [viewerId, sendMove]
+    [viewerId, sendMove, activePlayers, buildPlayerMetadata]
   )
 
   const nextCard = useCallback(() => {
     sendMove({
       type: 'NEXT_CARD',
-      playerId: viewerId || '',
+      playerId: TEAM_MOVE,
+      userId: viewerId || '',
       data: {},
     })
   }, [viewerId, sendMove])
@@ -197,16 +347,26 @@ export function RoomMemoryQuizProvider({ children }: { children: ReactNode }) {
   const showInputPhase = useCallback(() => {
     sendMove({
       type: 'SHOW_INPUT_PHASE',
-      playerId: viewerId || '',
+      playerId: TEAM_MOVE,
+      userId: viewerId || '',
       data: {},
     })
   }, [viewerId, sendMove])
 
   const acceptNumber = useCallback(
     (number: number) => {
+      // Clear local input immediately
+      setLocalCurrentInput('')
+
+      console.log('🚀 [acceptNumber] Sending ACCEPT_NUMBER move:', {
+        viewerId,
+        number,
+      })
+
       sendMove({
         type: 'ACCEPT_NUMBER',
-        playerId: viewerId || '',
+        playerId: TEAM_MOVE, // Team move - can't identify specific player
+        userId: viewerId || '', // User who guessed correctly
         data: { number },
       })
     },
@@ -214,28 +374,32 @@ export function RoomMemoryQuizProvider({ children }: { children: ReactNode }) {
   )
 
   const rejectNumber = useCallback(() => {
+    // Clear local input immediately
+    setLocalCurrentInput('')
+
+    console.log('🚀 [rejectNumber] Sending REJECT_NUMBER move:', {
+      viewerId,
+    })
+
     sendMove({
       type: 'REJECT_NUMBER',
-      playerId: viewerId || '',
+      playerId: TEAM_MOVE, // Team move - can't identify specific player
+      userId: viewerId || '', // User who guessed incorrectly
       data: {},
     })
   }, [viewerId, sendMove])
 
-  const setInput = useCallback(
-    (input: string) => {
-      sendMove({
-        type: 'SET_INPUT',
-        playerId: viewerId || '',
-        data: { input },
-      })
-    },
-    [viewerId, sendMove]
-  )
+  const setInput = useCallback((input: string) => {
+    // LOCAL ONLY - no network sync!
+    // This makes typing instant with zero network lag
+    setLocalCurrentInput(input)
+  }, [])
 
   const showResults = useCallback(() => {
     sendMove({
       type: 'SHOW_RESULTS',
-      playerId: viewerId || '',
+      playerId: TEAM_MOVE,
+      userId: viewerId || '',
       data: {},
     })
   }, [viewerId, sendMove])
@@ -243,24 +407,130 @@ export function RoomMemoryQuizProvider({ children }: { children: ReactNode }) {
   const resetGame = useCallback(() => {
     sendMove({
       type: 'RESET_QUIZ',
-      playerId: viewerId || '',
+      playerId: TEAM_MOVE,
+      userId: viewerId || '',
       data: {},
     })
   }, [viewerId, sendMove])
 
   const setConfig = useCallback(
-    (field: 'selectedCount' | 'displayTime' | 'selectedDifficulty', value: any) => {
+    (field: 'selectedCount' | 'displayTime' | 'selectedDifficulty' | 'playMode', value: any) => {
       sendMove({
         type: 'SET_CONFIG',
-        playerId: viewerId || '',
+        playerId: TEAM_MOVE,
+        userId: viewerId || '',
         data: { field, value },
       })
     },
     [viewerId, sendMove]
   )
 
+  // Merge network state with local input state
+  const mergedState = {
+    ...state,
+    currentInput: localCurrentInput, // Override network state with local input
+  }
+
+  // If state is corrupted, show error message instead of crashing
+  if (hasStateCorruption) {
+    return (
+      <div
+        style={{
+          display: 'flex',
+          flexDirection: 'column',
+          alignItems: 'center',
+          justifyContent: 'center',
+          padding: '40px',
+          textAlign: 'center',
+          minHeight: '400px',
+        }}
+      >
+        <div
+          style={{
+            fontSize: '48px',
+            marginBottom: '20px',
+          }}
+        >
+          ⚠️
+        </div>
+        <h2
+          style={{
+            fontSize: '24px',
+            fontWeight: 'bold',
+            marginBottom: '12px',
+            color: '#dc2626',
+          }}
+        >
+          Game State Mismatch
+        </h2>
+        <p
+          style={{
+            fontSize: '16px',
+            color: '#6b7280',
+            marginBottom: '24px',
+            maxWidth: '500px',
+          }}
+        >
+          There's a mismatch between game types in this room. This usually happens when room members
+          are playing different games.
+        </p>
+        <div
+          style={{
+            background: '#f9fafb',
+            border: '1px solid #e5e7eb',
+            borderRadius: '8px',
+            padding: '16px',
+            marginBottom: '24px',
+            maxWidth: '500px',
+          }}
+        >
+          <p
+            style={{
+              fontSize: '14px',
+              fontWeight: '600',
+              marginBottom: '8px',
+            }}
+          >
+            To fix this:
+          </p>
+          <ol
+            style={{
+              fontSize: '14px',
+              textAlign: 'left',
+              paddingLeft: '20px',
+              lineHeight: '1.6',
+            }}
+          >
+            <li>Make sure all room members are on the same game page</li>
+            <li>Try refreshing the page</li>
+            <li>If the issue persists, leave and rejoin the room</li>
+          </ol>
+        </div>
+        <button
+          onClick={() => window.location.reload()}
+          style={{
+            padding: '10px 20px',
+            background: '#3b82f6',
+            color: 'white',
+            border: 'none',
+            borderRadius: '6px',
+            fontSize: '14px',
+            fontWeight: '600',
+            cursor: 'pointer',
+          }}
+        >
+          Refresh Page
+        </button>
+      </div>
+    )
+  }
+
+  // Determine if current user is the room creator (controls card timing)
+  const isRoomCreator =
+    roomData?.members.find((member) => member.userId === viewerId)?.isCreator || false
+
   const contextValue: MemoryQuizContextValue = {
-    state,
+    state: mergedState,
     dispatch: () => {
       // No-op - replaced with action creators
       console.warn('dispatch() is deprecated in room mode, use action creators instead')
@@ -268,6 +538,7 @@ export function RoomMemoryQuizProvider({ children }: { children: ReactNode }) {
     isGameActive,
     resetGame,
     exitSession,
+    isRoomCreator, // Pass room creator flag to components
     // Expose action creators for components to use
     startQuiz,
     nextCard,

apps/web/src/app/arcade/memory-quiz/reducer.ts

@@ -12,6 +12,13 @@ export const initialState: SorobanQuizState = {
   guessesRemaining: 0,
   currentInput: '',
   incorrectGuesses: 0,
+  // Multiplayer state
+  activePlayers: [],
+  playerMetadata: {},
+  playerScores: {},
+  playMode: 'cooperative', // Default to cooperative
+  numberFoundBy: {},
+  // UI state
   gamePhase: 'setup',
   prefixAcceptanceTimeout: null,
   finishButtonsBound: false,
@@ -32,6 +39,8 @@ export function quizReducer(state: SorobanQuizState, action: QuizAction): Soroba
       return { ...state, selectedCount: action.count }
     case 'SET_DIFFICULTY':
       return { ...state, selectedDifficulty: action.difficulty }
+    case 'SET_PLAY_MODE':
+      return { ...state, playMode: action.playMode }
     case 'START_QUIZ':
       return {
         ...state,
@@ -46,19 +55,41 @@ export function quizReducer(state: SorobanQuizState, action: QuizAction): Soroba
       return { ...state, currentCardIndex: state.currentCardIndex + 1 }
     case 'SHOW_INPUT_PHASE':
       return { ...state, gamePhase: 'input' }
-    case 'ACCEPT_NUMBER':
+    case 'ACCEPT_NUMBER': {
+      // In competitive mode, track which player guessed correctly
+      const newPlayerScores = { ...state.playerScores }
+      if (state.playMode === 'competitive' && action.playerId) {
+        const currentScore = newPlayerScores[action.playerId] || { correct: 0, incorrect: 0 }
+        newPlayerScores[action.playerId] = {
+          ...currentScore,
+          correct: currentScore.correct + 1,
+        }
+      }
       return {
         ...state,
         foundNumbers: [...state.foundNumbers, action.number],
         currentInput: '',
+        playerScores: newPlayerScores,
+      }
+    }
+    case 'REJECT_NUMBER': {
+      // In competitive mode, track which player guessed incorrectly
+      const newPlayerScores = { ...state.playerScores }
+      if (state.playMode === 'competitive' && action.playerId) {
+        const currentScore = newPlayerScores[action.playerId] || { correct: 0, incorrect: 0 }
+        newPlayerScores[action.playerId] = {
+          ...currentScore,
+          incorrect: currentScore.incorrect + 1,
+        }
       }
-    case 'REJECT_NUMBER':
       return {
         ...state,
         guessesRemaining: state.guessesRemaining - 1,
         incorrectGuesses: state.incorrectGuesses + 1,
         currentInput: '',
+        playerScores: newPlayerScores,
       }
+    }
     case 'SET_INPUT':
       return { ...state, currentInput: action.input }
     case 'SET_PREFIX_TIMEOUT':
@@ -89,6 +120,7 @@ export function quizReducer(state: SorobanQuizState, action: QuizAction): Soroba
         displayTime: state.displayTime,
         selectedCount: state.selectedCount,
         selectedDifficulty: state.selectedDifficulty,
+        playMode: state.playMode, // Preserve play mode
         // Preserve keyboard state across resets
         hasPhysicalKeyboard: state.hasPhysicalKeyboard,
         testingMode: state.testingMode,

apps/web/src/app/arcade/memory-quiz/types.ts

@@ -1,9 +1,16 @@
+import type { PlayerMetadata } from '@/lib/arcade/player-ownership.client'
+
 export interface QuizCard {
   number: number
-  svgComponent: JSX.Element
+  svgComponent: JSX.Element | null
   element: HTMLElement | null
 }
 
+export interface PlayerScore {
+  correct: number
+  incorrect: number
+}
+
 export interface SorobanQuizState {
   // Core game data
   cards: QuizCard[]
@@ -22,6 +29,13 @@ export interface SorobanQuizState {
   currentInput: string
   incorrectGuesses: number
 
+  // Multiplayer state
+  activePlayers: string[]
+  playerMetadata: Record<string, PlayerMetadata>
+  playerScores: Record<string, PlayerScore>
+  playMode: 'cooperative' | 'competitive'
+  numberFoundBy: Record<number, string> // Maps number to userId who found it
+
   // UI state
   gamePhase: 'setup' | 'display' | 'input' | 'results'
   prefixAcceptanceTimeout: NodeJS.Timeout | null
@@ -43,11 +57,12 @@ export type QuizAction =
   | { type: 'SET_DISPLAY_TIME'; time: number }
   | { type: 'SET_SELECTED_COUNT'; count: number }
   | { type: 'SET_DIFFICULTY'; difficulty: DifficultyLevel }
+  | { type: 'SET_PLAY_MODE'; playMode: 'cooperative' | 'competitive' }
   | { type: 'START_QUIZ'; quizCards: QuizCard[] }
   | { type: 'NEXT_CARD' }
   | { type: 'SHOW_INPUT_PHASE' }
-  | { type: 'ACCEPT_NUMBER'; number: number }
-  | { type: 'REJECT_NUMBER' }
+  | { type: 'ACCEPT_NUMBER'; number: number; playerId?: string }
+  | { type: 'REJECT_NUMBER'; playerId?: string }
   | { type: 'ADD_WRONG_GUESS_ANIMATION'; number: number }
   | { type: 'CLEAR_WRONG_GUESS_ANIMATIONS' }
   | { type: 'SET_INPUT'; input: string }

apps/web/src/components/GameSelector.tsx

@@ -9,13 +9,13 @@ export const GAMES_CONFIG = {
   'memory-quiz': {
     name: 'Memory Lightning',
     fullName: 'Memory Lightning ⚡',
-    maxPlayers: 1,
+    maxPlayers: 4,
     description: 'Test your memory speed with rapid-fire abacus calculations',
     longDescription:
-      'Challenge yourself with lightning-fast memory tests. Perfect your mental math skills with this intense solo experience.',
+      'Challenge yourself or compete with friends in lightning-fast memory tests. Work together cooperatively or compete for the highest score!',
     url: '/arcade/memory-quiz',
     icon: '⚡',
-    chips: ['⭐ Beginner Friendly', '🔥 Speed Challenge', '🧮 Abacus Focus'],
+    chips: ['👥 Multiplayer', '🔥 Speed Challenge', '🧮 Abacus Focus'],
     color: 'green',
     gradient: 'linear-gradient(135deg, #dcfce7, #bbf7d0)',
     borderColor: 'green.200',

apps/web/src/hooks/__tests__/useOptimisticGameState.test.ts

@@ -42,6 +42,7 @@ describe('useOptimisticGameState', () => {
     const move: GameMove = {
       type: 'INCREMENT',
       playerId: 'test',
+      userId: 'test-user',
       timestamp: Date.now(),
       data: {},
     }
@@ -65,6 +66,7 @@ describe('useOptimisticGameState', () => {
     const move: GameMove = {
       type: 'INCREMENT',
       playerId: 'test',
+      userId: 'test-user',
       timestamp: 123,
       data: {},
     }
@@ -100,6 +102,7 @@ describe('useOptimisticGameState', () => {
     const move: GameMove = {
       type: 'INCREMENT',
       playerId: 'test',
+      userId: 'test-user',
       timestamp: 123,
       data: {},
     }
@@ -133,6 +136,7 @@ describe('useOptimisticGameState', () => {
     const move1: GameMove = {
       type: 'INCREMENT',
       playerId: 'test',
+      userId: 'test-user',
       timestamp: 123,
       data: {},
     }
@@ -140,6 +144,7 @@ describe('useOptimisticGameState', () => {
     const move2: GameMove = {
       type: 'INCREMENT',
       playerId: 'test',
+      userId: 'test-user',
       timestamp: 124,
       data: {},
     }
@@ -184,6 +189,7 @@ describe('useOptimisticGameState', () => {
       result.current.applyOptimisticMove({
         type: 'INCREMENT',
         playerId: 'test',
+        userId: 'test-user',
         timestamp: 123,
         data: {},
       })
@@ -215,6 +221,7 @@ describe('useOptimisticGameState', () => {
       result.current.applyOptimisticMove({
         type: 'INCREMENT',
         playerId: 'test',
+        userId: 'test-user',
         timestamp: 123,
         data: {},
       })
@@ -245,6 +252,7 @@ describe('useOptimisticGameState', () => {
     const move: GameMove = {
       type: 'INCREMENT',
       playerId: 'test',
+      userId: 'test-user',
       timestamp: 123,
       data: {},
     }

apps/web/src/lib/arcade/__tests__/session-manager.test.ts

@@ -260,6 +260,7 @@ describe('session-manager', () => {
         type: 'FLIP_CARD',
         data: { cardId: '1' },
         playerId: '1',
+        userId: mockUserId,
         timestamp: Date.now(),
       }
 

apps/web/src/lib/arcade/validation/MemoryQuizGameValidator.ts

@@ -30,10 +30,10 @@ export class MemoryQuizGameValidator
         return this.validateShowInputPhase(state)
 
       case 'ACCEPT_NUMBER':
-        return this.validateAcceptNumber(state, move.data.number)
+        return this.validateAcceptNumber(state, move.data.number, move.userId)
 
       case 'REJECT_NUMBER':
-        return this.validateRejectNumber(state)
+        return this.validateRejectNumber(state, move.userId)
 
       case 'SET_INPUT':
         return this.validateSetInput(state, move.data.input)
@@ -83,6 +83,24 @@ export class MemoryQuizGameValidator
       element: null,
     }))
 
+    // Extract multiplayer data from move
+    const activePlayers = data.activePlayers || state.activePlayers || []
+    const playerMetadata = data.playerMetadata || state.playerMetadata || {}
+
+    // Initialize player scores for all active players (by userId)
+    const uniqueUserIds = new Set<string>()
+    for (const playerId of activePlayers) {
+      const metadata = playerMetadata[playerId]
+      if (metadata?.userId) {
+        uniqueUserIds.add(metadata.userId)
+      }
+    }
+
+    const playerScores = Array.from(uniqueUserIds).reduce((acc: any, userId: string) => {
+      acc[userId] = { correct: 0, incorrect: 0 }
+      return acc
+    }, {})
+
     const newState: SorobanQuizState = {
       ...state,
       quizCards,
@@ -95,6 +113,11 @@ export class MemoryQuizGameValidator
       currentInput: '',
       wrongGuessAnimations: [],
       prefixAcceptanceTimeout: null,
+      // Multiplayer state
+      activePlayers,
+      playerMetadata,
+      playerScores,
+      numberFoundBy: {},
     }
 
     return {
@@ -143,7 +166,11 @@ export class MemoryQuizGameValidator
     }
   }
 
-  private validateAcceptNumber(state: SorobanQuizState, number: number): ValidationResult {
+  private validateAcceptNumber(
+    state: SorobanQuizState,
+    number: number,
+    userId?: string
+  ): ValidationResult {
     // Must be in input phase
     if (state.gamePhase !== 'input') {
       return {
@@ -174,10 +201,28 @@ export class MemoryQuizGameValidator
       }
     }
 
+    // Update player scores (track by userId)
+    const playerScores = state.playerScores || {}
+    const newPlayerScores = { ...playerScores }
+    const numberFoundBy = state.numberFoundBy || {}
+    const newNumberFoundBy = { ...numberFoundBy }
+
+    if (userId) {
+      const currentScore = newPlayerScores[userId] || { correct: 0, incorrect: 0 }
+      newPlayerScores[userId] = {
+        ...currentScore,
+        correct: currentScore.correct + 1,
+      }
+      // Track who found this number
+      newNumberFoundBy[number] = userId
+    }
+
     const newState: SorobanQuizState = {
       ...state,
       foundNumbers: [...state.foundNumbers, number],
       currentInput: '',
+      playerScores: newPlayerScores,
+      numberFoundBy: newNumberFoundBy,
     }
 
     return {
@@ -186,7 +231,7 @@ export class MemoryQuizGameValidator
     }
   }
 
-  private validateRejectNumber(state: SorobanQuizState): ValidationResult {
+  private validateRejectNumber(state: SorobanQuizState, userId?: string): ValidationResult {
     // Must be in input phase
     if (state.gamePhase !== 'input') {
       return {
@@ -203,11 +248,23 @@ export class MemoryQuizGameValidator
       }
     }
 
+    // Update player scores (track by userId)
+    const playerScores = state.playerScores || {}
+    const newPlayerScores = { ...playerScores }
+    if (userId) {
+      const currentScore = newPlayerScores[userId] || { correct: 0, incorrect: 0 }
+      newPlayerScores[userId] = {
+        ...currentScore,
+        incorrect: currentScore.incorrect + 1,
+      }
+    }
+
     const newState: SorobanQuizState = {
       ...state,
       guessesRemaining: state.guessesRemaining - 1,
       incorrectGuesses: state.incorrectGuesses + 1,
       currentInput: '',
+      playerScores: newPlayerScores,
     }
 
     return {
@@ -289,7 +346,7 @@ export class MemoryQuizGameValidator
 
   private validateSetConfig(
     state: SorobanQuizState,
-    field: 'selectedCount' | 'displayTime' | 'selectedDifficulty',
+    field: 'selectedCount' | 'displayTime' | 'selectedDifficulty' | 'playMode',
     value: any
   ): ValidationResult {
     // Can only change config during setup phase
@@ -320,6 +377,12 @@ export class MemoryQuizGameValidator
         }
         break
 
+      case 'playMode':
+        if (!['cooperative', 'competitive'].includes(value)) {
+          return { valid: false, error: `Invalid playMode: ${value}` }
+        }
+        break
+
       default:
         return { valid: false, error: `Unknown config field: ${field}` }
     }
@@ -355,6 +418,13 @@ export class MemoryQuizGameValidator
       guessesRemaining: 0,
       currentInput: '',
       incorrectGuesses: 0,
+      // Multiplayer state
+      activePlayers: [],
+      playerMetadata: {},
+      playerScores: {},
+      playMode: 'cooperative',
+      numberFoundBy: {},
+      // UI state
       gamePhase: 'setup',
       prefixAcceptanceTimeout: null,
       finishButtonsBound: false,

apps/web/src/lib/arcade/validation/types.ts

@@ -14,9 +14,17 @@ export interface ValidationResult {
   newState?: unknown
 }
 
+/**
+ * Sentinel value for team moves where no specific player can be identified
+ * Used in free-for-all games where all of a user's players act as a team
+ */
+export const TEAM_MOVE = '__TEAM__' as const
+export type TeamMoveSentinel = typeof TEAM_MOVE
+
 export interface GameMove {
   type: string
-  playerId: string
+  playerId: string | TeamMoveSentinel // Individual player (turn-based) or __TEAM__ (free-for-all)
+  userId: string // Room member/viewer who made the move
   timestamp: number
   data: unknown
 }
@@ -128,7 +136,7 @@ export interface MemoryQuizResetQuizMove extends GameMove {
 export interface MemoryQuizSetConfigMove extends GameMove {
   type: 'SET_CONFIG'
   data: {
-    field: 'selectedCount' | 'displayTime' | 'selectedDifficulty'
+    field: 'selectedCount' | 'displayTime' | 'selectedDifficulty' | 'playMode'
     value: any
   }
 }

package.json

@@ -1,6 +1,6 @@
 {
   "name": "soroban-monorepo",
-  "version": "3.14.3",
+  "version": "3.15.2",
   "private": true,
   "description": "Beautiful Soroban Flashcard Generator - Monorepo",
   "workspaces": [