chore(release): 3.22.3 [skip ci]

## [3.22.3](https://github.com/antialias/soroban-abacus-flashcards/compare/v3.22.2...v3.22.3) (2025-10-16)

### Bug Fixes

* **number-guesser:** add turn indicators, error feedback, and fix player ordering ([9f62623](9f62623684))

### Documentation

* **arcade:** update docs for unified validator registry ([6f6cb14](6f6cb14650))

CHANGELOG.md

@@ -1,3 +1,30 @@
+## [3.22.3](https://github.com/antialias/soroban-abacus-flashcards/compare/v3.22.2...v3.22.3) (2025-10-16)
+
+
+### Bug Fixes
+
+* **number-guesser:** add turn indicators, error feedback, and fix player ordering ([9f62623](https://github.com/antialias/soroban-abacus-flashcards/commit/9f626236845493ef68e1b3626e80efa35637b449))
+
+
+### Documentation
+
+* **arcade:** update docs for unified validator registry ([6f6cb14](https://github.com/antialias/soroban-abacus-flashcards/commit/6f6cb14650ba3636a7e2b036e2a2a9410492e7c3))
+
+## [3.22.2](https://github.com/antialias/soroban-abacus-flashcards/compare/v3.22.1...v3.22.2) (2025-10-16)
+
+
+### Code Refactoring
+
+* **arcade:** create unified validator registry to fix dual registration ([f775fc5](https://github.com/antialias/soroban-abacus-flashcards/commit/f775fc55e50af0c3a29b3e00fc722e7d7ce90212)), closes [#1](https://github.com/antialias/soroban-abacus-flashcards/issues/1)
+
+## [3.22.1](https://github.com/antialias/soroban-abacus-flashcards/compare/v3.22.0...v3.22.1) (2025-10-16)
+
+
+### Bug Fixes
+
+* **arcade:** add Number Guesser to game config helpers ([7d1a351](https://github.com/antialias/soroban-abacus-flashcards/commit/7d1a351ed6a1442ae34f6b75d46039bfa77a921b))
+* **nav:** update types for registry games with nullable gameName ([a51e539](https://github.com/antialias/soroban-abacus-flashcards/commit/a51e539d023681daf639ec104e79079c8ceec98e))
+
 ## [3.22.0](https://github.com/antialias/soroban-abacus-flashcards/compare/v3.21.0...v3.22.0) (2025-10-16)
 
 

apps/web/docs/AUDIT_MODULAR_GAME_SYSTEM.md

@@ -0,0 +1,519 @@
+# Modular Game System Audit
+
+**Date**: 2025-10-15
+**Updated**: 2025-10-15
+**Status**: ✅ CRITICAL ISSUE RESOLVED
+
+---
+
+## Executive Summary
+
+The modular game system **now meets its stated intentions** after implementing the unified validator registry. The critical dual registration issue has been resolved.
+
+**Original Issue**: Client-side implementation (SDK, registry, game definitions) was well-designed, but server-side validation used a hard-coded legacy system, breaking the core premise of modularity.
+
+**Resolution**: Created unified isomorphic validator registry (`src/lib/arcade/validators.ts`) that serves both client and server needs, with auto-derived GameName type.
+
+**Verdict**: ✅ **Production Ready** - System is now truly modular with single registration point
+
+---
+
+## Intention vs. Reality
+
+### Stated Intentions
+
+> "A modular, plugin-based architecture for building multiplayer arcade games"
+>
+> **Goals:**
+> 1. **Modularity**: Each game is self-contained and independently deployable
+> 2. Games register themselves with a central registry
+> 3. No need to modify core infrastructure when adding games
+
+### Current Reality
+
+✅ **Client-Side**: Fully modular, games use SDK and register themselves
+❌ **Server-Side**: Hard-coded validator map, requires manual code changes
+❌ **Overall**: **System is NOT modular** - adding a game requires editing 2 different registries
+
+---
+
+## Critical Issues
+
+### ✅ Issue #1: Dual Registration System (RESOLVED)
+
+**Original Problem**: Games had to register in TWO separate places:
+
+1. **Client Registry** (`src/lib/arcade/game-registry.ts`)
+2. **Server Validator Map** (`src/lib/arcade/validation/index.ts`)
+
+**Impact**:
+- ❌ Broke modularity - couldn't just drop in a new game
+- ❌ Easy to forget one registration, causing runtime errors
+- ❌ Violated DRY principle
+- ❌ Two sources of truth for "what games exist"
+
+**Resolution** (Implemented 2025-10-15):
+
+Created unified isomorphic validator registry at `src/lib/arcade/validators.ts`:
+
+```typescript
+export const validatorRegistry = {
+  matching: matchingGameValidator,
+  'memory-quiz': memoryQuizGameValidator,
+  'number-guesser': numberGuesserValidator,
+  // Add new games here - GameName type auto-updates!
+} as const
+
+// Auto-derived type - no manual updates needed!
+export type GameName = keyof typeof validatorRegistry
+```
+
+**Changes Made**:
+1. ✅ Created `src/lib/arcade/validators.ts` - Unified validator registry (isomorphic)
+2. ✅ Updated `validation/index.ts` - Now re-exports from unified registry (backwards compatible)
+3. ✅ Updated `validation/types.ts` - GameName now auto-derived (no more hard-coded union)
+4. ✅ Updated `session-manager.ts` - Imports from unified registry
+5. ✅ Updated `socket-server.ts` - Imports from unified registry
+6. ✅ Updated `route.ts` - Uses `hasValidator()` instead of hard-coded array
+7. ✅ Updated `game-config-helpers.ts` - Handles ExtendedGameName for legacy games
+8. ✅ Updated `game-registry.ts` - Added runtime validation check
+
+**Benefits**:
+- ✅ Single registration point for validators
+- ✅ Auto-derived GameName type (no manual updates)
+- ✅ Type-safe validator access
+- ✅ Backwards compatible with existing code
+- ✅ Runtime warnings for registration mismatches
+
+**Commit**: `refactor(arcade): create unified validator registry to fix dual registration` (9459f37b)
+
+---
+
+### ✅ Issue #2: Validators Not Accessible from Registry (RESOLVED)
+
+**Original Problem**: The `GameDefinition` contained validators, but server couldn't access them because `game-registry.ts` imported React components.
+
+**Resolution**: Created separate isomorphic validator registry that server can import without pulling in client-only code.
+
+**How It Works Now**:
+- `src/lib/arcade/validators.ts` - Isomorphic, server can import safely
+- `src/lib/arcade/game-registry.ts` - Client-only, imports React components
+- Both use the same validator instances (verified at runtime)
+
+**Benefits**:
+- ✅ Server has direct access to validators
+- ✅ No need for dual validator maps
+- ✅ Clear separation: validators (isomorphic) vs UI (client-only)
+
+---
+
+### ⚠️ Issue #3: Type System Fragmentation
+
+**Problem**: Multiple overlapping type definitions for same concepts:
+
+**GameValidator** has THREE definitions:
+1. `validation/types.ts` - Legacy validator interface
+2. `game-sdk/types.ts` - SDK validator interface (extends legacy)
+3. Individual game validators - Implement one or both?
+
+**GameMove** has TWO type systems:
+1. `validation/types.ts` - Legacy move types (MatchingFlipCardMove, etc.)
+2. Game-specific types in each game's `types.ts`
+
+**GameName** is hard-coded:
+```typescript
+// validation/types.ts:9
+export type GameName = 'matching' | 'memory-quiz' | 'complement-race' | 'number-guesser'
+```
+
+This must be manually updated for every new game!
+
+**Impact**:
+- Confusing which types to use
+- Easy to use wrong import
+- GameName type doesn't auto-update from registry
+
+---
+
+### ⚠️ Issue #4: Old Games Not Migrated
+
+**Problem**: Existing games (matching, memory-quiz) still use old structure:
+
+**Old Pattern** (matching, memory-quiz):
+```
+src/app/arcade/matching/
+  ├── context/           (Old pattern)
+  │   └── RoomMemoryPairsProvider.tsx
+  └── components/
+```
+
+**New Pattern** (number-guesser):
+```
+src/arcade-games/number-guesser/
+  ├── index.ts           (New pattern)
+  ├── Validator.ts
+  ├── Provider.tsx
+  └── components/
+```
+
+**Impact**:
+- Inconsistent codebase structure
+- Two different patterns developers must understand
+- Documentation shows new pattern, but most games use old pattern
+- Confusing for new developers
+
+**Evidence**:
+- `src/app/arcade/matching/` - Uses old structure
+- `src/app/arcade/memory-quiz/` - Uses old structure
+- `src/arcade-games/number-guesser/` - Uses new structure
+
+---
+
+### ✅ Issue #5: Manual GameName Type Updates (RESOLVED)
+
+**Original Problem**: `GameName` type was a hard-coded union that had to be manually updated for each new game.
+
+**Resolution**: Changed validator registry from Map to const object, enabling type derivation:
+
+```typescript
+// src/lib/arcade/validators.ts
+export const validatorRegistry = {
+  matching: matchingGameValidator,
+  'memory-quiz': memoryQuizGameValidator,
+  'number-guesser': numberGuesserValidator,
+  // Add new games here...
+} as const
+
+// Auto-derived! No manual updates needed!
+export type GameName = keyof typeof validatorRegistry
+```
+
+**Benefits**:
+- ✅ GameName type updates automatically when adding to registry
+- ✅ Impossible to forget type update (it's derived)
+- ✅ Single registration step (just add to validatorRegistry)
+- ✅ Type-safe throughout codebase
+
+---
+
+## Secondary Issues
+
+### Issue #6: No Server-Side Registry Access
+
+**Problem**: Server code cannot import `game-registry.ts` because it contains React components.
+
+**Why**:
+- `GameDefinition` includes `Provider` and `GameComponent` (React components)
+- Server-side code runs in Node.js, can't import React components
+- No way to access just the validator from registry
+
+**Potential Solutions**:
+1. Split registry into isomorphic and client-only parts
+2. Separate validator registration from game registration
+3. Use conditional exports in package.json
+
+---
+
+### Issue #7: Documentation Doesn't Match Reality
+
+**Problem**: Documentation describes a fully modular system, but reality requires manual edits in multiple places.
+
+**From README.md**:
+> "Step 7: Register Game - Add to src/lib/arcade/game-registry.ts"
+
+**Missing Steps**:
+- Also add to `validation/index.ts` validator map
+- Also add to `GameName` type union
+- Import validator in server files
+
+**Impact**: Developers follow docs, game doesn't work, confusion ensues.
+
+---
+
+### Issue #8: No Validation of Registered Games
+
+**Problem**: Registration is type-safe but has no runtime validation:
+
+```typescript
+registerGame(numberGuesserGame)  // No validation that validator works
+```
+
+**Missing Checks**:
+- Does validator implement all required methods?
+- Does manifest match expected schema?
+- Are all required fields present?
+- Does validator.getInitialState() return valid state?
+
+**Impact**: Bugs only caught at runtime when game is played.
+
+---
+
+## Proposed Solutions
+
+### Solution 1: Unified Server-Side Registry (RECOMMENDED)
+
+**Create isomorphic validator registry**:
+
+```typescript
+// src/lib/arcade/validators.ts (NEW FILE - isomorphic)
+import { numberGuesserValidator } from '@/arcade-games/number-guesser/Validator'
+import { matchingGameValidator } from '@/lib/arcade/validation/MatchingGameValidator'
+// ... other validators
+
+export const validatorRegistry = new Map([
+  ['number-guesser', numberGuesserValidator],
+  ['matching', matchingGameValidator],
+  // ...
+])
+
+export function getValidator(gameName: string) {
+  const validator = validatorRegistry.get(gameName)
+  if (!validator) throw new Error(`No validator for game: ${gameName}`)
+  return validator
+}
+
+export type GameName = keyof typeof validatorRegistry  // Auto-derived!
+```
+
+**Update game-registry.ts** to use this:
+
+```typescript
+// src/lib/arcade/game-registry.ts
+import { getValidator } from './validators'
+
+export function registerGame(game: GameDefinition) {
+  const { name } = game.manifest
+
+  // Verify validator is registered server-side
+  const validator = getValidator(name)
+  if (validator !== game.validator) {
+    console.warn(`[Registry] Validator mismatch for ${name}`)
+  }
+
+  registry.set(name, game)
+}
+```
+
+**Pros**:
+- Single source of truth for validators
+- Auto-derived GameName type
+- Client and server use same validator
+- Only one registration needed
+
+**Cons**:
+- Still requires manual import in validators.ts
+- Doesn't solve "drop in a game" fully
+
+---
+
+### Solution 2: Code Generation
+
+**Auto-generate validator registry from file system**:
+
+```typescript
+// scripts/generate-registry.ts
+// Scans src/arcade-games/**/Validator.ts
+// Generates validators.ts and game-registry imports
+```
+
+**Pros**:
+- Truly modular - just add folder, run build
+- No manual registration
+- Auto-derived types
+
+**Cons**:
+- Build-time complexity
+- Magic (harder to understand)
+- May not work with all bundlers
+
+---
+
+### Solution 3: Split GameDefinition
+
+**Separate client and server concerns**:
+
+```typescript
+// Isomorphic (client + server)
+export interface GameValidatorDefinition {
+  name: string
+  validator: GameValidator
+  defaultConfig: GameConfig
+}
+
+// Client-only
+export interface GameUIDefinition {
+  name: string
+  manifest: GameManifest
+  Provider: GameProviderComponent
+  GameComponent: GameComponent
+}
+
+// Combined (client-only)
+export interface GameDefinition extends GameValidatorDefinition, GameUIDefinition {}
+```
+
+**Pros**:
+- Clear separation of concerns
+- Server can import just validator definition
+- Type-safe
+
+**Cons**:
+- More complexity
+- Still requires two registries
+
+---
+
+## Immediate Action Items
+
+### Critical (Do Before Next Game)
+
+1. **✅ Document the dual registration requirement** (COMPLETED)
+   - ✅ Update README with both registration steps
+   - ✅ Add troubleshooting section for "game not found" errors
+   - ✅ Document unified validator registry in Step 7
+
+2. **✅ Unify validator registration** (COMPLETED 2025-10-15)
+   - ✅ Chose Solution 1 (Unified Server-Side Registry)
+   - ✅ Implemented unified registry (src/lib/arcade/validators.ts)
+   - ✅ Updated session-manager.ts and socket-server.ts
+   - ✅ Tested with number-guesser (no TypeScript errors)
+
+3. **✅ Auto-derive GameName type** (COMPLETED 2025-10-15)
+   - ✅ Removed hard-coded union
+   - ✅ Derive from validator registry using `keyof typeof`
+   - ✅ Updated all usages (backwards compatible via re-exports)
+
+### High Priority
+
+4. **🟡 Migrate old games to new pattern**
+   - Move matching to `arcade-games/matching/`
+   - Move memory-quiz to `arcade-games/memory-quiz/`
+   - Update imports and tests
+   - OR document that old games use old pattern (transitional)
+
+5. **🟡 Add validator registration validation**
+   - Runtime check in registerGame()
+   - Warn if validator missing
+   - Validate manifest schema
+
+### Medium Priority
+
+6. **🟢 Clean up type definitions**
+   - Consolidate GameValidator types
+   - Single source of truth for GameMove
+   - Clear documentation on which to use
+
+7. **🟢 Update documentation**
+   - Add "dual registry" warning
+   - Update step-by-step guide
+   - Add troubleshooting for common mistakes
+
+---
+
+## Architectural Debt
+
+### Technical Debt Accumulated
+
+1. **Old validation system** (`validation/types.ts`, `validation/index.ts`)
+   - Used by server-side code
+   - Hard-coded game list
+   - No migration path documented
+
+2. **Mixed game structures** (old in `app/arcade/`, new in `arcade-games/`)
+   - Confusing for developers
+   - Inconsistent imports
+   - Harder to maintain
+
+3. **Type fragmentation** (3 GameValidator definitions)
+   - Unclear which to use
+   - Potential for bugs
+   - Harder to refactor
+
+### Migration Path
+
+**Option A: Big Bang** (Risky)
+- Migrate all games to new structure in one PR
+- Update server to use unified registry
+- High risk of breakage
+
+**Option B: Incremental** (Safer)
+- Document dual registration as "current reality"
+- Create unified validator registry (doesn't break old games)
+- Slowly migrate old games one by one
+- Eventually deprecate old validation system
+
+**Recommendation**: Option B (Incremental)
+
+---
+
+## Compliance with Intentions
+
+| Intention | Status | Notes |
+|-----------|--------|-------|
+| Modularity | ✅ Pass | Single registration in validators.ts + game-registry.ts |
+| Self-registration | ✅ Pass | Both client and server use unified registry |
+| Type safety | ✅ Pass | Good TypeScript coverage + auto-derived GameName |
+| No core changes | ⚠️ Improved | Must edit validators.ts, but one central file |
+| Drop-in games | ⚠️ Improved | Two registration points (validator + game def) |
+| Stable SDK API | ✅ Pass | SDK is well-designed and consistent |
+| Clear patterns | ⚠️ Partial | New pattern is clear, but old games don't follow it |
+
+**Original Grade**: **D** (Failed core modularity requirement)
+**Current Grade**: **B+** (Modularity achieved, some legacy migration pending)
+
+---
+
+## Positive Aspects (What Works Well)
+
+1. **✅ SDK Design** - Clean, well-documented, type-safe
+2. **✅ Client-Side Registry** - Simple, effective pattern
+3. **✅ GameDefinition Structure** - Good separation of concerns
+4. **✅ Documentation** - Comprehensive (though doesn't match reality)
+5. **✅ defineGame() Helper** - Makes game creation easy
+6. **✅ Type Safety** - Excellent TypeScript coverage
+7. **✅ Number Guesser Example** - Good reference implementation
+
+---
+
+## Recommendations
+
+### Immediate (This Sprint)
+
+1. ✅ **Document current reality** - Update docs to show both registrations required
+2. 🔴 **Create unified validator registry** - Implement Solution 1
+3. 🔴 **Update server to use unified registry** - Modify session-manager.ts and socket-server.ts
+
+### Next Sprint
+
+4. 🟡 **Migrate one old game** - Move matching to new structure as proof of concept
+5. 🟡 **Add registration validation** - Runtime checks for validator consistency
+6. 🟡 **Auto-derive GameName** - Remove hard-coded type union
+
+### Future
+
+7. 🟢 **Code generation** - Explore automated registry generation
+8. 🟢 **Plugin system** - True drop-in games with discovery
+9. 🟢 **Deprecate old validation system** - Once all games migrated
+
+---
+
+## Conclusion
+
+The modular game system has a **solid foundation** but is **not truly modular** due to server-side technical debt. The client-side implementation is excellent, but the server still uses a legacy hard-coded validation system.
+
+**Status**: Needs significant refactoring before claiming "modular architecture"
+
+**Path Forward**: Implement unified validator registry (Solution 1), then incrementally migrate old games.
+
+**Risk**: If we add more games before fixing this, technical debt will compound.
+
+---
+
+*This audit was conducted by reviewing:*
+- `src/lib/arcade/game-registry.ts`
+- `src/lib/arcade/validation/index.ts`
+- `src/lib/arcade/session-manager.ts`
+- `src/socket-server.ts`
+- `src/lib/arcade/game-sdk/`
+- `src/arcade-games/number-guesser/`
+- Documentation in `docs/` and `src/arcade-games/README.md`

apps/web/src/app/api/arcade/rooms/route.ts

@@ -3,7 +3,7 @@ import { createRoom, listActiveRooms } from '@/lib/arcade/room-manager'
 import { addRoomMember, getRoomMembers, isMember } from '@/lib/arcade/room-membership'
 import { getRoomActivePlayers } from '@/lib/arcade/player-manager'
 import { getViewerId } from '@/lib/viewer'
-import type { GameName } from '@/lib/arcade/validation'
+import { hasValidator, type GameName } from '@/lib/arcade/validators'
 
 /**
  * GET /api/arcade/rooms
@@ -72,8 +72,7 @@ export async function POST(req: NextRequest) {
 
     // Validate game name if provided (gameName is now optional)
     if (body.gameName) {
-      const validGames: GameName[] = ['matching', 'memory-quiz', 'complement-race']
-      if (!validGames.includes(body.gameName)) {
+      if (!hasValidator(body.gameName)) {
         return NextResponse.json({ error: 'Invalid game name' }, { status: 400 })
       }
     }

apps/web/src/arcade-games/README.md

@@ -0,0 +1,816 @@
+# Arcade Game System
+
+A modular, plugin-based architecture for building multiplayer arcade games with real-time synchronization.
+
+## Table of Contents
+
+- [Overview](#overview)
+- [Architecture](#architecture)
+- [Game SDK](#game-sdk)
+- [Creating a New Game](#creating-a-new-game)
+- [File Structure](#file-structure)
+- [Examples](#examples)
+- [Best Practices](#best-practices)
+- [Troubleshooting](#troubleshooting)
+
+---
+
+## Overview
+
+### Goals
+
+1. **Modularity**: Each game is self-contained and independently deployable
+2. **Type Safety**: Full TypeScript support with compile-time validation
+3. **Real-time Sync**: Built-in multiplayer support via WebSocket
+4. **Optimistic Updates**: Instant client feedback with server validation
+5. **Consistent UX**: Shared navigation, player management, and room features
+
+### Key Features
+
+- **Plugin Architecture**: Games register themselves with a central registry
+- **Stable SDK API**: Games only import from `@/lib/arcade/game-sdk`
+- **Server-side Validation**: All moves validated server-side with client rollback
+- **Automatic State Sync**: Multi-client synchronization handled automatically
+- **Turn Indicators**: Built-in UI for showing active player
+- **Error Handling**: Standardized error feedback to users
+
+---
+
+## Architecture
+
+### System Components
+
+```
+┌─────────────────────────────────────────────────────────────┐
+│                     Game Registry                            │
+│  - Registers all available games                            │
+│  - Provides game discovery                                  │
+└─────────────────────────────────────────────────────────────┘
+                            │
+                            ▼
+┌─────────────────────────────────────────────────────────────┐
+│                      Game SDK                                │
+│  - Stable API surface for games                             │
+│  - React hooks (useArcadeSession, useRoomData, etc.)        │
+│  - Type definitions and utilities                           │
+└─────────────────────────────────────────────────────────────┘
+                            │
+                            ▼
+┌─────────────────────────────────────────────────────────────┐
+│                   Individual Games                           │
+│  number-guesser/                                            │
+│    ├── index.ts          (Game definition)                  │
+│    ├── Validator.ts      (Server validation)                │
+│    ├── Provider.tsx      (Client state management)          │
+│    ├── GameComponent.tsx (Main UI)                          │
+│    ├── types.ts          (TypeScript types)                 │
+│    └── components/       (Phase UIs)                        │
+└─────────────────────────────────────────────────────────────┘
+```
+
+### Data Flow
+
+```
+User Action → Provider (sendMove)
+              ↓
+        useArcadeSession
+              ↓
+        Optimistic Update (instant UI feedback)
+              ↓
+        WebSocket → Server
+              ↓
+        Validator.validateMove()
+              ↓
+        ✓ Valid: State Update → Broadcast
+        ✗ Invalid: Reject → Client Rollback
+              ↓
+        Client receives validated state
+```
+
+---
+
+## Game SDK
+
+### Core API Surface
+
+```typescript
+import {
+  // Types
+  type GameDefinition,
+  type GameValidator,
+  type GameState,
+  type GameMove,
+  type GameConfig,
+  type ValidationResult,
+
+  // React Hooks
+  useArcadeSession,
+  useRoomData,
+  useGameMode,
+  useViewerId,
+  useUpdateGameConfig,
+
+  // Utilities
+  defineGame,
+  buildPlayerMetadata,
+
+} from '@/lib/arcade/game-sdk'
+```
+
+### Key Concepts
+
+#### GameDefinition
+
+Complete description of a game:
+
+```typescript
+interface GameDefinition<TConfig, TState, TMove> {
+  manifest: GameManifest          // Display info, max players, etc.
+  Provider: GameProviderComponent // React context provider
+  GameComponent: GameComponent    // Main UI component
+  validator: GameValidator        // Server-side validation
+  defaultConfig: TConfig          // Default game settings
+}
+```
+
+#### GameState
+
+The complete game state that's synchronized across all clients:
+
+```typescript
+interface GameState {
+  gamePhase: string                          // Current phase (setup, playing, results)
+  activePlayers: string[]                    // Array of player IDs
+  playerMetadata: Record<string, PlayerMeta> // Player info (name, emoji, etc.)
+  // ... game-specific state
+}
+```
+
+#### GameMove
+
+Actions that players take, validated server-side:
+
+```typescript
+interface GameMove {
+  type: string           // Move type (e.g., 'FLIP_CARD', 'MAKE_GUESS')
+  playerId: string       // Player making the move
+  userId: string         // User ID (for authentication)
+  timestamp: number      // Client timestamp
+  data: Record<string, unknown> // Move-specific payload
+}
+```
+
+#### GameValidator
+
+Server-side validation logic:
+
+```typescript
+interface GameValidator<TState, TMove> {
+  validateMove(state: TState, move: TMove): ValidationResult
+  isGameComplete(state: TState): boolean
+  getInitialState(config: unknown): TState
+}
+```
+
+---
+
+## Creating a New Game
+
+### Step 1: Create Game Directory
+
+```bash
+mkdir -p src/arcade-games/my-game/components
+```
+
+### Step 2: Define Types (`types.ts`)
+
+```typescript
+import type { GameConfig, GameMove, GameState } from '@/lib/arcade/game-sdk'
+
+// Game configuration (persisted to database)
+export interface MyGameConfig extends GameConfig {
+  difficulty: number
+  timer: number
+}
+
+// Game state (synchronized across clients)
+export interface MyGameState extends GameState {
+  gamePhase: 'setup' | 'playing' | 'results'
+  activePlayers: string[]
+  playerMetadata: Record<string, PlayerMetadata>
+  currentPlayer: string
+  score: Record<string, number>
+  // ... your game-specific state
+}
+
+// Move types
+export type MyGameMove =
+  | { type: 'START_GAME'; playerId: string; userId: string; timestamp: number; data: { activePlayers: string[] } }
+  | { type: 'MAKE_MOVE'; playerId: string; userId: string; timestamp: number; data: { /* move data */ } }
+  | { type: 'END_GAME'; playerId: string; userId: string; timestamp: number; data: {} }
+```
+
+### Step 3: Create Validator (`Validator.ts`)
+
+```typescript
+import type { GameValidator, ValidationResult } from '@/lib/arcade/game-sdk'
+import type { MyGameState, MyGameMove } from './types'
+
+export class MyGameValidator implements GameValidator<MyGameState, MyGameMove> {
+  validateMove(state: MyGameState, move: MyGameMove): ValidationResult {
+    switch (move.type) {
+      case 'START_GAME':
+        return this.validateStartGame(state, move.data.activePlayers)
+      case 'MAKE_MOVE':
+        return this.validateMakeMove(state, move.playerId, move.data)
+      default:
+        return { valid: false, error: 'Unknown move type' }
+    }
+  }
+
+  private validateStartGame(state: MyGameState, activePlayers: string[]): ValidationResult {
+    if (activePlayers.length < 2) {
+      return { valid: false, error: 'Need at least 2 players' }
+    }
+
+    const newState: MyGameState = {
+      ...state,
+      gamePhase: 'playing',
+      activePlayers,
+      currentPlayer: activePlayers[0],
+      score: activePlayers.reduce((acc, p) => ({ ...acc, [p]: 0 }), {}),
+    }
+
+    return { valid: true, newState }
+  }
+
+  // ... more validation methods
+
+  isGameComplete(state: MyGameState): boolean {
+    return state.gamePhase === 'results'
+  }
+
+  getInitialState(config: unknown): MyGameState {
+    const { difficulty, timer } = config as MyGameConfig
+    return {
+      difficulty,
+      timer,
+      gamePhase: 'setup',
+      activePlayers: [],
+      playerMetadata: {},
+      currentPlayer: '',
+      score: {},
+    }
+  }
+}
+
+export const myGameValidator = new MyGameValidator()
+```
+
+### Step 4: Create Provider (`Provider.tsx`)
+
+```typescript
+'use client'
+
+import { createContext, useCallback, useContext, useMemo } from 'react'
+import {
+  type GameMove,
+  buildPlayerMetadata,
+  useArcadeSession,
+  useGameMode,
+  useRoomData,
+  useViewerId,
+} from '@/lib/arcade/game-sdk'
+import type { MyGameState } from './types'
+
+interface MyGameContextValue {
+  state: MyGameState
+  lastError: string | null
+  startGame: () => void
+  makeMove: (data: any) => void
+  clearError: () => void
+  exitSession: () => void
+}
+
+const MyGameContext = createContext<MyGameContextValue | null>(null)
+
+export function useMyGame() {
+  const context = useContext(MyGameContext)
+  if (!context) throw new Error('useMyGame must be used within MyGameProvider')
+  return context
+}
+
+export function MyGameProvider({ children }: { children: React.ReactNode }) {
+  const { data: viewerId } = useViewerId()
+  const { roomData } = useRoomData()
+  const { activePlayers: activePlayerIds, players } = useGameMode()
+
+  // Get active players as array (keep Set iteration order to match UI display)
+  const activePlayers = Array.from(activePlayerIds)
+
+  const initialState = useMemo(() => ({
+    difficulty: 1,
+    timer: 30,
+    gamePhase: 'setup' as const,
+    activePlayers: [],
+    playerMetadata: {},
+    currentPlayer: '',
+    score: {},
+  }), [])
+
+  const { state, sendMove, exitSession, lastError, clearError } =
+    useArcadeSession<MyGameState>({
+      userId: viewerId || '',
+      roomId: roomData?.id,
+      initialState,
+      applyMove: (state, move) => state, // Server handles all updates
+    })
+
+  const startGame = useCallback(() => {
+    const playerMetadata = buildPlayerMetadata(activePlayers, {}, players, viewerId)
+
+    sendMove({
+      type: 'START_GAME',
+      playerId: activePlayers[0],
+      userId: viewerId || '',
+      data: { activePlayers, playerMetadata },
+    })
+  }, [activePlayers, players, viewerId, sendMove])
+
+  const makeMove = useCallback((data: any) => {
+    sendMove({
+      type: 'MAKE_MOVE',
+      playerId: state.currentPlayer,
+      userId: viewerId || '',
+      data,
+    })
+  }, [state.currentPlayer, viewerId, sendMove])
+
+  return (
+    <MyGameContext.Provider value={{
+      state,
+      lastError,
+      startGame,
+      makeMove,
+      clearError,
+      exitSession,
+    }}>
+      {children}
+    </MyGameContext.Provider>
+  )
+}
+```
+
+### Step 5: Create Game Component (`GameComponent.tsx`)
+
+```typescript
+'use client'
+
+import { useRouter } from 'next/navigation'
+import { PageWithNav } from '@/components/PageWithNav'
+import { useMyGame } from '../Provider'
+import { SetupPhase } from './SetupPhase'
+import { PlayingPhase } from './PlayingPhase'
+import { ResultsPhase } from './ResultsPhase'
+
+export function GameComponent() {
+  const router = useRouter()
+  const { state, exitSession } = useMyGame()
+
+  // Determine whose turn it is for the turn indicator
+  const currentPlayerId = state.gamePhase === 'playing' ? state.currentPlayer : undefined
+
+  return (
+    <PageWithNav
+      navTitle="My Game"
+      navEmoji="🎮"
+      emphasizePlayerSelection={state.gamePhase === 'setup'}
+      currentPlayerId={currentPlayerId}
+      playerScores={state.score}
+      onExitSession={() => {
+        exitSession()
+        router.push('/arcade')
+      }}
+    >
+      {state.gamePhase === 'setup' && <SetupPhase />}
+      {state.gamePhase === 'playing' && <PlayingPhase />}
+      {state.gamePhase === 'results' && <ResultsPhase />}
+    </PageWithNav>
+  )
+}
+```
+
+### Step 6: Define Game (`index.ts`)
+
+```typescript
+import { defineGame } from '@/lib/arcade/game-sdk'
+import type { GameManifest } from '@/lib/arcade/game-sdk'
+import { GameComponent } from './components/GameComponent'
+import { MyGameProvider } from './Provider'
+import type { MyGameConfig, MyGameMove, MyGameState } from './types'
+import { myGameValidator } from './Validator'
+
+const manifest: GameManifest = {
+  name: 'my-game',
+  displayName: 'My Awesome Game',
+  icon: '🎮',
+  description: 'A fun multiplayer game',
+  longDescription: 'Detailed description of gameplay...',
+  maxPlayers: 4,
+  difficulty: 'Beginner',
+  chips: ['👥 Multiplayer', '🎲 Turn-Based'],
+  color: 'blue',
+  gradient: 'linear-gradient(135deg, #bfdbfe, #93c5fd)',
+  borderColor: 'blue.200',
+  available: true,
+}
+
+const defaultConfig: MyGameConfig = {
+  difficulty: 1,
+  timer: 30,
+}
+
+export const myGame = defineGame<MyGameConfig, MyGameState, MyGameMove>({
+  manifest,
+  Provider: MyGameProvider,
+  GameComponent,
+  validator: myGameValidator,
+  defaultConfig,
+})
+```
+
+### Step 7: Register Game
+
+#### 7a. Register Validator (Server-Side)
+
+Add your validator to the unified registry in `src/lib/arcade/validators.ts`:
+
+```typescript
+import { myGameValidator } from '@/arcade-games/my-game/Validator'
+
+export const validatorRegistry = {
+  matching: matchingGameValidator,
+  'memory-quiz': memoryQuizGameValidator,
+  'number-guesser': numberGuesserValidator,
+  'my-game': myGameValidator,  // Add your game here!
+  // GameName type will auto-update from these keys
+} as const
+```
+
+**Why**: The validator registry is isomorphic (runs on both client and server) and serves as the single source of truth for all game validators. Adding your validator here automatically:
+- Makes it available for server-side move validation
+- Updates the `GameName` type (no manual type updates needed!)
+- Enables your game for multiplayer rooms
+
+#### 7b. Register Game Definition (Client-Side)
+
+Add to `src/lib/arcade/game-registry.ts`:
+
+```typescript
+import { myGame } from '@/arcade-games/my-game'
+
+registerGame(myGame)
+```
+
+**Why**: The game registry is client-only and connects your game's UI components (Provider, GameComponent) with the arcade system. Registration happens on client init and verifies that your validator is also registered server-side.
+
+**Verification**: When you register a game, the registry will warn you if:
+- ⚠️  The validator is missing from `validators.ts`
+- ⚠️  The validator instance doesn't match (different imports)
+
+**Important**: Both steps are required for a working game. The validator registry handles server logic, while the game registry handles client UI.
+
+---
+
+## File Structure
+
+```
+src/arcade-games/my-game/
+├── index.ts                 # Game definition and export
+├── Validator.ts             # Server-side move validation
+├── Provider.tsx             # Client state management
+├── GameComponent.tsx        # Main UI wrapper
+├── types.ts                 # TypeScript type definitions
+└── components/
+    ├── SetupPhase.tsx       # Setup/lobby UI
+    ├── PlayingPhase.tsx     # Main gameplay UI
+    └── ResultsPhase.tsx     # End game/scores UI
+```
+
+### File Responsibilities
+
+| File | Purpose | Runs On |
+|------|---------|---------|
+| `index.ts` | Game registration | Both |
+| `Validator.ts` | Move validation, game logic | **Server only** |
+| `Provider.tsx` | State management, API calls | Client only |
+| `GameComponent.tsx` | Navigation, phase routing | Client only |
+| `types.ts` | Shared type definitions | Both |
+| `components/*` | UI for each game phase | Client only |
+
+---
+
+## Examples
+
+### Number Guesser (Turn-Based)
+
+See `src/arcade-games/number-guesser/` for a complete example of:
+- Turn-based gameplay (chooser → guessers)
+- Player rotation logic
+- Round management
+- Score tracking
+- Hot/cold feedback system
+- Error handling and user feedback
+
+**Key Patterns:**
+- Setting `currentPlayerId` for turn indicators
+- Rotating turns in validator
+- Handling round vs. game completion
+- Type coercion for JSON-serialized numbers
+
+---
+
+## Best Practices
+
+### 1. Player Ordering Consistency
+
+**Problem**: Sets don't guarantee order, causing mismatch between UI and game logic.
+
+**Solution**: Use `Array.from(activePlayerIds)` without sorting in both UI and game logic.
+
+```typescript
+// In Provider
+const activePlayers = Array.from(activePlayerIds) // NO .sort()
+
+// In Validator
+const newState = {
+  ...state,
+  currentPlayer: activePlayers[0], // First in Set order = first in UI
+}
+```
+
+### 2. Type Coercion for Numbers
+
+**Problem**: WebSocket JSON serialization converts numbers to strings.
+
+**Solution**: Explicitly coerce in validator:
+
+```typescript
+validateMove(state: MyGameState, move: MyGameMove): ValidationResult {
+  switch (move.type) {
+    case 'MAKE_GUESS':
+      return this.validateGuess(state, Number(move.data.guess)) // Coerce!
+  }
+}
+```
+
+### 3. Error Feedback
+
+**Problem**: Users don't see why their moves were rejected.
+
+**Solution**: Use `lastError` from `useArcadeSession`:
+
+```typescript
+const { state, lastError, clearError } = useArcadeSession(...)
+
+// Auto-dismiss after 5 seconds
+useEffect(() => {
+  if (lastError) {
+    const timeout = setTimeout(() => clearError(), 5000)
+    return () => clearTimeout(timeout)
+  }
+}, [lastError, clearError])
+
+// Show in UI
+{lastError && (
+  <div className="error-banner">
+    <div>⚠️ Move Rejected</div>
+    <div>{lastError}</div>
+    <button onClick={clearError}>Dismiss</button>
+  </div>
+)}
+```
+
+### 4. Turn Indicators
+
+**Problem**: Players don't know whose turn it is.
+
+**Solution**: Pass `currentPlayerId` to `PageWithNav`:
+
+```typescript
+<PageWithNav
+  currentPlayerId={state.currentPlayer}
+  playerScores={state.scores}
+>
+```
+
+### 5. Server-Only Logic
+
+**Problem**: Client can cheat by modifying local state.
+
+**Solution**: All game logic in validator, client uses `applyMove: (state) => state`:
+
+```typescript
+// ❌ BAD: Client calculates winner
+const { state, sendMove } = useArcadeSession({
+  applyMove: (state, move) => {
+    if (move.type === 'SCORE') {
+      return { ...state, winner: calculateWinner(state) } // Cheatable!
+    }
+  }
+})
+
+// ✅ GOOD: Server calculates everything
+const { state, sendMove } = useArcadeSession({
+  applyMove: (state, move) => state // Client just waits for server
+})
+```
+
+### 6. Phase Management
+
+Use discriminated union for type-safe phase rendering:
+
+```typescript
+type GamePhase = 'setup' | 'playing' | 'results'
+
+interface MyGameState {
+  gamePhase: GamePhase
+  // ...
+}
+
+// In GameComponent
+{state.gamePhase === 'setup' && <SetupPhase />}
+{state.gamePhase === 'playing' && <PlayingPhase />}
+{state.gamePhase === 'results' && <ResultsPhase />}
+```
+
+---
+
+## Troubleshooting
+
+### "Player not found" errors
+
+**Cause**: Player IDs from `useGameMode()` don't match server state.
+
+**Fix**: Always use `buildPlayerMetadata()` helper:
+
+```typescript
+const playerMetadata = buildPlayerMetadata(activePlayers, {}, players, viewerId)
+```
+
+### Turn indicator not showing
+
+**Cause**: `currentPlayerId` not passed or doesn't match player IDs in UI.
+
+**Fix**: Verify player order matches between game state and `activePlayerIds`:
+
+```typescript
+// Both should use same source without sorting
+const activePlayers = Array.from(activePlayerIds) // Provider
+const activePlayerList = Array.from(activePlayers) // PageWithNav
+```
+
+### Moves rejected with type errors
+
+**Cause**: JSON serialization converts numbers to strings.
+
+**Fix**: Add `Number()` coercion in validator:
+
+```typescript
+case 'SET_VALUE':
+  return this.validateValue(state, Number(move.data.value))
+```
+
+### State not syncing across clients
+
+**Cause**: Not using `useArcadeSession` correctly.
+
+**Fix**: Ensure `roomId` is passed:
+
+```typescript
+const { state, sendMove } = useArcadeSession({
+  userId: viewerId || '',
+  roomId: roomData?.id, // Required for room sync!
+  initialState,
+  applyMove: (state) => state,
+})
+```
+
+### Game not appearing in selector
+
+**Cause**: Not registered or `available: false`.
+
+**Fix**:
+1. Add to `game-registry.ts`: `registerGame(myGame)`
+2. Set `available: true` in manifest
+3. Verify no console errors on import
+
+### Config changes not taking effect
+
+**Cause**: State sync timing - validator uses old state while config is being updated.
+
+**Context**: When you change game config (e.g., min/max numbers), there's a brief window where:
+1. Client updates config in database
+2. Config change hasn't propagated to server state yet
+3. Moves are validated against old state
+
+**Fix**: Ensure config changes trigger state reset or are applied atomically:
+
+```typescript
+// When changing config, also update initialState
+const setConfig = useCallback((field, value) => {
+  sendMove({ type: 'SET_CONFIG', data: { field, value } })
+
+  // Persist to database for next session
+  if (roomData?.id) {
+    updateGameConfig({
+      roomId: roomData.id,
+      gameConfig: {
+        ...roomData.gameConfig,
+        'my-game': { ...currentConfig, [field]: value }
+      }
+    })
+  }
+}, [sendMove, updateGameConfig, roomData])
+```
+
+**Best Practice**: Make config changes only during setup phase, before game starts.
+
+### Debugging validation errors
+
+**Problem**: Moves rejected but unclear why (especially type-related issues).
+
+**Solution**: Add debug logging in validator:
+
+```typescript
+private validateGuess(state: State, guess: number): ValidationResult {
+  // Debug logging
+  console.log('[MyGame] Validating guess:', {
+    guess,
+    guessType: typeof guess,           // Check if it's a string!
+    min: state.minNumber,
+    minType: typeof state.minNumber,
+    max: state.maxNumber,
+    maxType: typeof state.maxNumber,
+  })
+
+  if (guess < state.minNumber || guess > state.maxNumber) {
+    return { valid: false, error: `Guess must be between ${state.minNumber} and ${state.maxNumber}` }
+  }
+
+  // ... rest of validation
+}
+```
+
+**What to check:**
+1. **Browser console**: Look for `[ArcadeSession] Move rejected by server:` messages
+2. **Server logs**: Check validator console.log output for types and values
+3. **Type mismatches**: Numbers becoming strings is the #1 issue
+4. **State sync**: Is the validator using the state you expect?
+
+**Common debugging workflow:**
+1. Move rejected → Check browser console for error message
+2. Error unclear → Add console.log to validator
+3. Restart server → See debug output when move is made
+4. Compare expected vs. actual values/types
+5. Add `Number()` coercion if types don't match
+
+---
+
+## Resources
+
+- **Game SDK**: `src/lib/arcade/game-sdk/`
+- **Registry**: `src/lib/arcade/game-registry.ts`
+- **Example Game**: `src/arcade-games/number-guesser/`
+- **Validation Types**: `src/lib/arcade/validation/types.ts`
+
+---
+
+## FAQ
+
+**Q: Can I use external libraries in my game?**
+A: Yes, but install them in the workspace package.json. Games should be self-contained.
+
+**Q: How do I add game configuration that persists?**
+A: Use `useUpdateGameConfig()` to save to room:
+
+```typescript
+const { mutate: updateGameConfig } = useUpdateGameConfig()
+
+updateGameConfig({
+  roomId: roomData.id,
+  gameConfig: {
+    ...roomData.gameConfig,
+    'my-game': { difficulty: 5 }
+  }
+})
+```
+
+**Q: Can I have asymmetric player roles?**
+A: Yes! See Number Guesser's chooser/guesser pattern.
+
+**Q: How do I handle real-time timers?**
+A: Store `startTime` in state, use client-side countdown, server validates elapsed time.
+
+**Q: What's the difference between `playerId` and `userId`?**
+A: `userId` is the user account, `playerId` is the avatar/character in the game. One user can control multiple players.

apps/web/src/arcade-games/number-guesser/Provider.tsx

@@ -22,12 +22,14 @@ import type { NumberGuesserState } from './types'
  */
 interface NumberGuesserContextValue {
   state: NumberGuesserState
+  lastError: string | null
   startGame: () => void
   chooseNumber: (number: number) => void
   makeGuess: (guess: number) => void
   nextRound: () => void
   goToSetup: () => void
   setConfig: (field: 'minNumber' | 'maxNumber' | 'roundsToWin', value: number) => void
+  clearError: () => void
   exitSession: () => void
 }
 
@@ -62,7 +64,7 @@ export function NumberGuesserProvider({ children }: { children: ReactNode }) {
   const { activePlayers: activePlayerIds, players } = useGameMode()
   const { mutate: updateGameConfig } = useUpdateGameConfig()
 
-  // Get active players as array
+  // Get active players as array (keep Set iteration order to match UI display)
   const activePlayers = Array.from(activePlayerIds)
 
   // Merge saved config from room
@@ -90,12 +92,13 @@ export function NumberGuesserProvider({ children }: { children: ReactNode }) {
   }, [roomData?.gameConfig])
 
   // Arcade session integration
-  const { state, sendMove, exitSession } = useArcadeSession<NumberGuesserState>({
-    userId: viewerId || '',
-    roomId: roomData?.id,
-    initialState,
-    applyMove: applyMoveOptimistically,
-  })
+  const { state, sendMove, exitSession, lastError, clearError } =
+    useArcadeSession<NumberGuesserState>({
+      userId: viewerId || '',
+      roomId: roomData?.id,
+      initialState,
+      applyMove: applyMoveOptimistically,
+    })
 
   // Action creators
   const startGame = useCallback(() => {
@@ -195,12 +198,14 @@ export function NumberGuesserProvider({ children }: { children: ReactNode }) {
 
   const contextValue: NumberGuesserContextValue = {
     state,
+    lastError,
     startGame,
     chooseNumber,
     makeGuess,
     nextRound,
     goToSetup,
     setConfig,
+    clearError,
     exitSession,
   }
 

apps/web/src/arcade-games/number-guesser/Validator.ts

@@ -14,10 +14,17 @@ export class NumberGuesserValidator
         return this.validateStartGame(state, move.data.activePlayers, move.data.playerMetadata)
 
       case 'CHOOSE_NUMBER':
-        return this.validateChooseNumber(state, move.data.secretNumber, move.playerId)
+        // Ensure secretNumber is a number (JSON deserialization can make it a string)
+        return this.validateChooseNumber(state, Number(move.data.secretNumber), move.playerId)
 
       case 'MAKE_GUESS':
-        return this.validateMakeGuess(state, move.data.guess, move.playerId, move.data.playerName)
+        // Ensure guess is a number (JSON deserialization can make it a string)
+        return this.validateMakeGuess(
+          state,
+          Number(move.data.guess),
+          move.playerId,
+          move.data.playerName
+        )
 
       case 'NEXT_ROUND':
         return this.validateNextRound(state)
@@ -26,7 +33,8 @@ export class NumberGuesserValidator
         return this.validateGoToSetup(state)
 
       case 'SET_CONFIG':
-        return this.validateSetConfig(state, move.data.field, move.data.value)
+        // Ensure value is a number (JSON deserialization can make it a string)
+        return this.validateSetConfig(state, move.data.field, Number(move.data.value))
 
       default:
         return {
@@ -88,6 +96,12 @@ export class NumberGuesserValidator
       }
     }
 
+    // Debug logging
+    console.log('[NumberGuesser] Setting secret number:', {
+      secretNumber,
+      secretNumberType: typeof secretNumber,
+    })
+
     // First guesser is the next player after chooser
     const chooserIndex = state.activePlayers.indexOf(state.chooser)
     const firstGuesserIndex = (chooserIndex + 1) % state.activePlayers.length
@@ -128,7 +142,17 @@ export class NumberGuesserValidator
       return { valid: false, error: 'No secret number set' }
     }
 
+    // Debug logging
+    console.log('[NumberGuesser] Validating guess:', {
+      guess,
+      guessType: typeof guess,
+      secretNumber: state.secretNumber,
+      secretNumberType: typeof state.secretNumber,
+    })
+
     const distance = Math.abs(guess - state.secretNumber)
+
+    console.log('[NumberGuesser] Calculated distance:', distance)
     const newGuess = {
       playerId,
       playerName,
@@ -181,8 +205,16 @@ export class NumberGuesserValidator
   }
 
   private validateNextRound(state: NumberGuesserState): ValidationResult {
-    if (state.gamePhase !== 'guessing' || !state.winner) {
-      return { valid: false, error: 'Cannot start next round yet' }
+    if (state.gamePhase !== 'guessing') {
+      return { valid: false, error: 'Not in guessing phase' }
+    }
+
+    // Check if the round is complete (someone guessed correctly)
+    const roundComplete =
+      state.guesses.length > 0 && state.guesses[state.guesses.length - 1].distance === 0
+
+    if (!roundComplete) {
+      return { valid: false, error: 'Round not complete yet - no one has guessed the number' }
     }
 
     // Rotate chooser to next player

apps/web/src/arcade-games/number-guesser/components/GameComponent.tsx

@@ -17,11 +17,21 @@ export function GameComponent() {
   const router = useRouter()
   const { state, exitSession, goToSetup } = useNumberGuesser()
 
+  // Determine whose turn it is based on game phase
+  const currentPlayerId =
+    state.gamePhase === 'choosing'
+      ? state.chooser
+      : state.gamePhase === 'guessing'
+        ? state.currentGuesser
+        : undefined
+
   return (
     <PageWithNav
       navTitle="Number Guesser"
       navEmoji="🎯"
       emphasizePlayerSelection={state.gamePhase === 'setup'}
+      currentPlayerId={currentPlayerId}
+      playerScores={state.scores}
       onExitSession={() => {
         exitSession?.()
         router.push('/arcade')

apps/web/src/arcade-games/number-guesser/components/GuessingPhase.tsx

@@ -4,13 +4,13 @@
 
 'use client'
 
-import { useState } from 'react'
+import { useEffect, useState } from 'react'
 import { useViewerId } from '@/lib/arcade/game-sdk'
 import { css } from '../../../../styled-system/css'
 import { useNumberGuesser } from '../Provider'
 
 export function GuessingPhase() {
-  const { state, makeGuess, nextRound } = useNumberGuesser()
+  const { state, makeGuess, nextRound, lastError, clearError } = useNumberGuesser()
   const { data: viewerId } = useViewerId()
   const [inputValue, setInputValue] = useState('')
 
@@ -21,6 +21,14 @@ export function GuessingPhase() {
   const lastGuess = state.guesses[state.guesses.length - 1]
   const roundJustEnded = lastGuess?.distance === 0
 
+  // Auto-clear error after 5 seconds
+  useEffect(() => {
+    if (lastError) {
+      const timeout = setTimeout(() => clearError(), 5000)
+      return () => clearTimeout(timeout)
+    }
+  }, [lastError, clearError])
+
   const handleSubmit = () => {
     const guess = Number.parseInt(inputValue, 10)
     if (Number.isNaN(guess)) return
@@ -84,6 +92,81 @@ export function GuessingPhase() {
         </p>
       </div>
 
+      {/* Error Banner */}
+      {lastError && (
+        <div
+          className={css({
+            background: 'linear-gradient(135deg, #fef2f2, #fee2e2)',
+            border: '2px solid',
+            borderColor: 'red.300',
+            borderRadius: '12px',
+            padding: '16px 20px',
+            marginBottom: '24px',
+            display: 'flex',
+            alignItems: 'center',
+            justifyContent: 'space-between',
+            animation: 'slideIn 0.3s ease',
+          })}
+        >
+          <div
+            className={css({
+              display: 'flex',
+              alignItems: 'center',
+              gap: '12px',
+            })}
+          >
+            <div
+              className={css({
+                fontSize: '24px',
+              })}
+            >
+              ⚠️
+            </div>
+            <div>
+              <div
+                className={css({
+                  fontSize: 'md',
+                  fontWeight: 'bold',
+                  color: 'red.700',
+                  marginBottom: '4px',
+                })}
+              >
+                Move Rejected
+              </div>
+              <div
+                className={css({
+                  fontSize: 'sm',
+                  color: 'red.600',
+                })}
+              >
+                {lastError}
+              </div>
+            </div>
+          </div>
+          <button
+            type="button"
+            onClick={clearError}
+            className={css({
+              padding: '8px 12px',
+              background: 'white',
+              border: '1px solid',
+              borderColor: 'red.300',
+              borderRadius: '6px',
+              fontSize: 'sm',
+              fontWeight: '600',
+              color: 'red.700',
+              cursor: 'pointer',
+              transition: 'all 0.2s',
+              _hover: {
+                background: 'red.50',
+              },
+            })}
+          >
+            Dismiss
+          </button>
+        </div>
+      )}
+
       {/* Round ended - show next round button */}
       {roundJustEnded && (
         <div

apps/web/src/components/nav/AddPlayerButton.tsx

@@ -26,7 +26,7 @@ interface AddPlayerButtonProps {
   // Context-aware: show different content based on room state
   isInRoom?: boolean
   // Game info for room creation
-  gameName?: 'matching' | 'memory-quiz' | 'complement-race'
+  gameName?: string | null
 }
 
 export function AddPlayerButton({
@@ -38,7 +38,7 @@ export function AddPlayerButton({
   activeTab: activeTabProp,
   setActiveTab: setActiveTabProp,
   isInRoom = false,
-  gameName = 'Arcade',
+  gameName = null,
 }: AddPlayerButtonProps) {
   const popoverRef = React.useRef<HTMLDivElement>(null)
   const router = useRouter()

apps/web/src/components/nav/GameContextNav.tsx

@@ -28,7 +28,7 @@ interface NetworkPlayer {
 interface ArcadeRoomInfo {
   roomId?: string
   roomName?: string
-  gameName: string
+  gameName: string | null
   playerCount: number
   joinCode?: string
 }
@@ -200,6 +200,7 @@ export function GameContextNav({
             onSetup={onSetup}
             onNewGame={onNewGame}
             onQuit={onExitSession}
+            showMenu={true}
           />
           <div style={{ marginLeft: 'auto' }}>
             <GameModeIndicator
@@ -287,7 +288,7 @@ export function GameContextNav({
                   playerScores={playerScores}
                   playerStreaks={playerStreaks}
                   roomId={roomInfo?.roomId}
-                  currentUserId={currentUserId}
+                  currentUserId={currentUserId ?? undefined}
                   isCurrentUserHost={isCurrentUserHost}
                 />
               ))}

apps/web/src/components/nav/JoinRoomModal.tsx

@@ -2,7 +2,7 @@ import { useEffect, useState } from 'react'
 import { io } from 'socket.io-client'
 import { Modal } from '@/components/common/Modal'
 import type { schema } from '@/db'
-import { useRoomData } from '@/hooks/useRoomData'
+import { useGetRoomByCode, useJoinRoom } from '@/hooks/useRoomData'
 
 export interface JoinRoomModalProps {
   /**
@@ -25,7 +25,8 @@ export interface JoinRoomModalProps {
  * Modal for joining a room by entering a 6-character code
  */
 export function JoinRoomModal({ isOpen, onClose, onSuccess }: JoinRoomModalProps) {
-  const { getRoomByCode, joinRoom } = useRoomData()
+  const { mutateAsync: getRoomByCode } = useGetRoomByCode()
+  const { mutate: joinRoom } = useJoinRoom()
   const [code, setCode] = useState('')
   const [password, setPassword] = useState('')
   const [error, setError] = useState('')

apps/web/src/components/nav/RecentRoomsList.tsx

@@ -4,7 +4,7 @@ import { getRoomDisplayWithEmoji } from '@/utils/room-display'
 interface RecentRoom {
   code: string
   name: string | null
-  gameName: string
+  gameName: string | null
   joinedAt: number
 }
 
@@ -105,7 +105,7 @@ export function RecentRoomsList({ onSelectRoom }: RecentRoomsListProps) {
                 {getRoomDisplayWithEmoji({
                   name: room.name,
                   code: room.code,
-                  gameName: room.gameName,
+                  gameName: room.gameName ?? undefined,
                 })}
               </span>
             </div>
@@ -133,7 +133,7 @@ export function RecentRoomsList({ onSelectRoom }: RecentRoomsListProps) {
 export function addToRecentRooms(room: {
   code: string
   name: string | null
-  gameName: string
+  gameName: string | null
 }): void {
   try {
     const stored = localStorage.getItem(STORAGE_KEY)

apps/web/src/hooks/useArcadeSession.ts

@@ -46,6 +46,11 @@ export interface UseArcadeSessionReturn<TState> {
    */
   hasPendingMoves: boolean
 
+  /**
+   * Last error from server (move rejection)
+   */
+  lastError: string | null
+
   /**
    * Send a game move (applies optimistically and sends to server)
    * Note: playerId must be provided by caller (not omitted)
@@ -57,6 +62,11 @@ export interface UseArcadeSessionReturn<TState> {
    */
   exitSession: () => void
 
+  /**
+   * Clear the last error
+   */
+  clearError: () => void
+
   /**
    * Manually sync with server (useful after reconnect)
    */
@@ -172,8 +182,10 @@ export function useArcadeSession<TState>(
     version: optimistic.version,
     connected,
     hasPendingMoves: optimistic.hasPendingMoves,
+    lastError: optimistic.lastError,
     sendMove,
     exitSession,
+    clearError: optimistic.clearError,
     refresh,
   }
 }

apps/web/src/hooks/useOptimisticGameState.ts

@@ -46,6 +46,11 @@ export interface UseOptimisticGameStateReturn<TState> {
    */
   hasPendingMoves: boolean
 
+  /**
+   * Last error from server (move rejection)
+   */
+  lastError: string | null
+
   /**
    * Apply a move optimistically and send to server
    */
@@ -66,6 +71,11 @@ export interface UseOptimisticGameStateReturn<TState> {
    */
   syncWithServer: (serverState: TState, serverVersion: number) => void
 
+  /**
+   * Clear the last error
+   */
+  clearError: () => void
+
   /**
    * Reset to initial state
    */
@@ -94,6 +104,9 @@ export function useOptimisticGameState<TState>(
   // Pending moves that haven't been confirmed by server yet
   const [pendingMoves, setPendingMoves] = useState<PendingMove<TState>[]>([])
 
+  // Last error from move rejection
+  const [lastError, setLastError] = useState<string | null>(null)
+
   // Ref for callbacks to avoid stale closures
   const callbacksRef = useRef({ onMoveAccepted, onMoveRejected })
   useEffect(() => {
@@ -152,6 +165,9 @@ export function useOptimisticGameState<TState>(
   )
 
   const handleMoveRejected = useCallback((error: string, rejectedMove: GameMove) => {
+    // Set the error for UI display
+    setLastError(error)
+
     // Remove the rejected move and all subsequent moves from pending queue
     setPendingMoves((prev) => {
       const index = prev.findIndex(
@@ -176,20 +192,27 @@ export function useOptimisticGameState<TState>(
     setPendingMoves([])
   }, [])
 
+  const clearError = useCallback(() => {
+    setLastError(null)
+  }, [])
+
   const reset = useCallback(() => {
     setServerState(initialState)
     setServerVersion(1)
     setPendingMoves([])
+    setLastError(null)
   }, [initialState])
 
   return {
     state: currentState,
     version: serverVersion,
     hasPendingMoves: pendingMoves.length > 0,
+    lastError,
     applyOptimisticMove,
     handleMoveAccepted,
     handleMoveRejected,
     syncWithServer,
+    clearError,
     reset,
   }
 }

apps/web/src/lib/arcade/game-config-helpers.ts

@@ -8,18 +8,25 @@
 import { and, eq } from 'drizzle-orm'
 import { createId } from '@paralleldrive/cuid2'
 import { db, schema } from '@/db'
-import type { GameName } from './validation'
+import type { GameName } from './validators'
 import type { GameConfigByName } from './game-configs'
 import {
   DEFAULT_MATCHING_CONFIG,
   DEFAULT_MEMORY_QUIZ_CONFIG,
   DEFAULT_COMPLEMENT_RACE_CONFIG,
+  DEFAULT_NUMBER_GUESSER_CONFIG,
 } from './game-configs'
 
+/**
+ * Extended game name type that includes both registered validators and legacy games
+ * TODO: Remove 'complement-race' once migrated to the new modular system
+ */
+type ExtendedGameName = GameName | 'complement-race'
+
 /**
  * Get default config for a game
  */
-function getDefaultGameConfig(gameName: GameName): GameConfigByName[GameName] {
+function getDefaultGameConfig(gameName: ExtendedGameName): GameConfigByName[ExtendedGameName] {
   switch (gameName) {
     case 'matching':
       return DEFAULT_MATCHING_CONFIG
@@ -27,6 +34,8 @@ function getDefaultGameConfig(gameName: GameName): GameConfigByName[GameName] {
       return DEFAULT_MEMORY_QUIZ_CONFIG
     case 'complement-race':
       return DEFAULT_COMPLEMENT_RACE_CONFIG
+    case 'number-guesser':
+      return DEFAULT_NUMBER_GUESSER_CONFIG
     default:
       throw new Error(`Unknown game: ${gameName}`)
   }
@@ -36,7 +45,7 @@ function getDefaultGameConfig(gameName: GameName): GameConfigByName[GameName] {
  * Get game-specific config from database with defaults
  * Type-safe: returns the correct config type based on gameName
  */
-export async function getGameConfig<T extends GameName>(
+export async function getGameConfig<T extends ExtendedGameName>(
   roomId: string,
   gameName: T
 ): Promise<GameConfigByName[T]> {
@@ -62,7 +71,7 @@ export async function getGameConfig<T extends GameName>(
  * Set (upsert) a game's config in the database
  * Creates a new row if it doesn't exist, updates if it does
  */
-export async function setGameConfig<T extends GameName>(
+export async function setGameConfig<T extends ExtendedGameName>(
   roomId: string,
   gameName: T,
   config: Partial<GameConfigByName[T]>
@@ -110,7 +119,7 @@ export async function setGameConfig<T extends GameName>(
  * Convenience wrapper around setGameConfig
  */
 export async function updateGameConfigField<
-  T extends GameName,
+  T extends ExtendedGameName,
   K extends keyof GameConfigByName[T],
 >(roomId: string, gameName: T, field: K, value: GameConfigByName[T][K]): Promise<void> {
   // Create a partial config with just the field being updated
@@ -123,7 +132,7 @@ export async function updateGameConfigField<
  * Delete a game's config from the database
  * Useful when clearing game selection or cleaning up
  */
-export async function deleteGameConfig(roomId: string, gameName: GameName): Promise<void> {
+export async function deleteGameConfig(roomId: string, gameName: ExtendedGameName): Promise<void> {
   await db
     .delete(schema.roomGameConfigs)
     .where(
@@ -139,14 +148,14 @@ export async function deleteGameConfig(roomId: string, gameName: GameName): Prom
  */
 export async function getAllGameConfigs(
   roomId: string
-): Promise<Partial<Record<GameName, unknown>>> {
+): Promise<Partial<Record<ExtendedGameName, unknown>>> {
   const configs = await db.query.roomGameConfigs.findMany({
     where: eq(schema.roomGameConfigs.roomId, roomId),
   })
 
-  const result: Partial<Record<GameName, unknown>> = {}
+  const result: Partial<Record<ExtendedGameName, unknown>> = {}
   for (const config of configs) {
-    result[config.gameName as GameName] = config.config
+    result[config.gameName as ExtendedGameName] = config.config
   }
 
   return result
@@ -165,7 +174,7 @@ export async function deleteAllGameConfigs(roomId: string): Promise<void> {
  * Validate a game config at runtime
  * Returns true if the config is valid for the given game
  */
-export function validateGameConfig(gameName: GameName, config: any): boolean {
+export function validateGameConfig(gameName: ExtendedGameName, config: any): boolean {
   switch (gameName) {
     case 'matching':
       return (
@@ -194,6 +203,18 @@ export function validateGameConfig(gameName: GameName, config: any): boolean {
       // TODO: Add validation when complement-race settings are defined
       return typeof config === 'object' && config !== null
 
+    case 'number-guesser':
+      return (
+        typeof config === 'object' &&
+        config !== null &&
+        typeof config.minNumber === 'number' &&
+        typeof config.maxNumber === 'number' &&
+        typeof config.roundsToWin === 'number' &&
+        config.minNumber >= 1 &&
+        config.maxNumber > config.minNumber &&
+        config.roundsToWin >= 1
+      )
+
     default:
       return false
   }

apps/web/src/lib/arcade/game-registry.ts

@@ -31,6 +31,28 @@ export function registerGame<
     throw new Error(`Game "${name}" is already registered`)
   }
 
+  // Verify validator is also registered server-side
+  try {
+    const { hasValidator, getValidator } = require('./validators')
+    if (!hasValidator(name)) {
+      console.error(
+        `⚠️  Game "${name}" registered but validator not found in server registry!` +
+          `\n   Add to src/lib/arcade/validators.ts to enable multiplayer.`
+      )
+    } else {
+      const serverValidator = getValidator(name)
+      if (serverValidator !== game.validator) {
+        console.warn(
+          `⚠️  Game "${name}" has different validator instances (client vs server).` +
+            `\n   This may cause issues. Ensure both use the same import.`
+        )
+      }
+    }
+  } catch (error) {
+    // If validators.ts can't be imported (e.g., in browser), skip check
+    // This is expected - validator registry is isomorphic but check only runs server-side
+  }
+
   registry.set(name, game)
   console.log(`✅ Registered game: ${name}`)
 }

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

@@ -6,7 +6,8 @@
 import { eq } from 'drizzle-orm'
 import { db, schema } from '@/db'
 import { buildPlayerOwnershipMap, type PlayerOwnershipMap } from './player-ownership'
-import { type GameMove, type GameName, getValidator } from './validation'
+import { getValidator, type GameName } from './validators'
+import type { GameMove } from './validation/types'
 
 export interface CreateSessionOptions {
   userId: string // User who owns/created the session (typically room creator)

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

@@ -1,29 +1,19 @@
 /**
  * Game validator registry
- * Maps game names to their validators
+ * @deprecated This file now re-exports from the unified registry
+ * New code should import from '@/lib/arcade/validators' instead
  */
 
-import { matchingGameValidator } from './MatchingGameValidator'
-import { memoryQuizGameValidator } from './MemoryQuizGameValidator'
-import { numberGuesserValidator } from '@/arcade-games/number-guesser/Validator'
-import type { GameName, GameValidator } from './types'
+// Re-export everything from unified registry
+export {
+  getValidator,
+  hasValidator,
+  getRegisteredGameNames,
+  validatorRegistry,
+  matchingGameValidator,
+  memoryQuizGameValidator,
+  numberGuesserValidator,
+} from '../validators'
 
-const validators = new Map<GameName, GameValidator>([
-  ['matching', matchingGameValidator],
-  ['memory-quiz', memoryQuizGameValidator],
-  ['number-guesser', numberGuesserValidator],
-  // Add other game validators here as they're implemented
-])
-
-export function getValidator(gameName: GameName): GameValidator {
-  const validator = validators.get(gameName)
-  if (!validator) {
-    throw new Error(`No validator found for game: ${gameName}`)
-  }
-  return validator
-}
-
-export { matchingGameValidator } from './MatchingGameValidator'
-export { memoryQuizGameValidator } from './MemoryQuizGameValidator'
-export { numberGuesserValidator } from '@/arcade-games/number-guesser/Validator'
+export type { GameName } from '../validators'
 export * from './types'

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

@@ -6,7 +6,11 @@
 import type { MemoryPairsState } from '@/app/games/matching/context/types'
 import type { SorobanQuizState } from '@/app/arcade/memory-quiz/types'
 
-export type GameName = 'matching' | 'memory-quiz' | 'complement-race' | 'number-guesser'
+/**
+ * Game name type - auto-derived from validator registry
+ * @deprecated Import from '@/lib/arcade/validators' instead
+ */
+export type { GameName } from '../validators'
 
 export interface ValidationResult {
   valid: boolean

apps/web/src/lib/arcade/validators.ts

@@ -0,0 +1,68 @@
+/**
+ * Unified Validator Registry (Isomorphic - runs on client AND server)
+ *
+ * This is the single source of truth for game validators.
+ * Both client and server import validators from here.
+ *
+ * To add a new game:
+ * 1. Import the validator
+ * 2. Add to validatorRegistry Map
+ * 3. GameName type will auto-update
+ */
+
+import { matchingGameValidator } from './validation/MatchingGameValidator'
+import { memoryQuizGameValidator } from './validation/MemoryQuizGameValidator'
+import { numberGuesserValidator } from '@/arcade-games/number-guesser/Validator'
+import type { GameValidator } from './validation/types'
+
+/**
+ * Central registry of all game validators
+ * Key: game name (matches manifest.name)
+ * Value: validator instance
+ */
+export const validatorRegistry = {
+  matching: matchingGameValidator,
+  'memory-quiz': memoryQuizGameValidator,
+  'number-guesser': numberGuesserValidator,
+  // Add new games here - GameName type will auto-update
+} as const
+
+/**
+ * Auto-derived game name type from registry
+ * No need to manually update this!
+ */
+export type GameName = keyof typeof validatorRegistry
+
+/**
+ * Get validator for a game
+ * @throws Error if game not found (fail fast)
+ */
+export function getValidator(gameName: string): GameValidator {
+  const validator = validatorRegistry[gameName as GameName]
+  if (!validator) {
+    throw new Error(
+      `No validator found for game: ${gameName}. ` +
+        `Available games: ${Object.keys(validatorRegistry).join(', ')}`
+    )
+  }
+  return validator
+}
+
+/**
+ * Check if a game has a registered validator
+ */
+export function hasValidator(gameName: string): gameName is GameName {
+  return gameName in validatorRegistry
+}
+
+/**
+ * Get all registered game names
+ */
+export function getRegisteredGameNames(): GameName[] {
+  return Object.keys(validatorRegistry) as GameName[]
+}
+
+/**
+ * Re-export validators for backwards compatibility
+ */
+export { matchingGameValidator, memoryQuizGameValidator, numberGuesserValidator }

apps/web/src/socket-server.ts

@@ -13,8 +13,8 @@ import {
 import { createRoom, getRoomById } from './lib/arcade/room-manager'
 import { getRoomMembers, getUserRooms, setMemberOnline } from './lib/arcade/room-membership'
 import { getRoomActivePlayers, getRoomPlayerIds } from './lib/arcade/player-manager'
-import type { GameMove, GameName } from './lib/arcade/validation'
-import { getValidator } from './lib/arcade/validation'
+import { getValidator, type GameName } from './lib/arcade/validators'
+import type { GameMove } from './lib/arcade/validation/types'
 import { getGameConfig } from './lib/arcade/game-config-helpers'
 
 // Use globalThis to store socket.io instance to avoid module isolation issues

apps/web/tsconfig.server.json

@@ -19,10 +19,24 @@
     "src/db/schema/**/*.ts",
     "src/db/migrate.ts",
     "src/lib/arcade/**/*.ts",
+    "src/arcade-games/**/Validator.ts",
+    "src/arcade-games/**/types.ts",
     "src/app/games/matching/context/types.ts",
     "src/app/games/matching/utils/cardGeneration.ts",
     "src/app/games/matching/utils/matchValidation.ts",
+    "src/app/arcade/memory-quiz/types.ts",
     "src/socket-server.ts"
   ],
-  "exclude": ["node_modules", "dist", "**/*.test.ts", "**/*.test.tsx", "**/*.spec.ts"]
+  "exclude": [
+    "node_modules",
+    "dist",
+    "src/components/**/*",
+    "src/contexts/**/*",
+    "src/hooks/**/*",
+    "src/stories/**/*",
+    "src/utils/**/*",
+    "**/*.test.ts",
+    "**/*.test.tsx",
+    "**/*.spec.ts"
+  ]
 }

package.json

@@ -1,6 +1,6 @@
 {
   "name": "soroban-monorepo",
-  "version": "3.22.0",
+  "version": "3.22.3",
   "private": true,
   "description": "Beautiful Soroban Flashcard Generator - Monorepo",
   "workspaces": [