diff --git a/frontend/project_plans/PHASE_F0_foundation.json b/frontend/project_plans/PHASE_F0_foundation.json
index 0461230..7248aa9 100644
--- a/frontend/project_plans/PHASE_F0_foundation.json
+++ b/frontend/project_plans/PHASE_F0_foundation.json
@@ -6,7 +6,7 @@
     "created": "2026-01-30",
     "lastUpdated": "2026-01-30",
     "totalTasks": 8,
-    "completedTasks": 6,
+    "completedTasks": 7,
     "status": "in_progress"
   },
   "tasks": [
@@ -123,8 +123,8 @@
       "description": "WebSocket connection manager",
       "category": "api",
       "priority": 6,
-      "completed": false,
-      "tested": false,
+      "completed": true,
+      "tested": true,
       "dependencies": ["F0-001", "F0-004"],
       "files": [
         {"path": "src/socket/client.ts", "status": "create"},
diff --git a/frontend/src/socket/client.spec.ts b/frontend/src/socket/client.spec.ts
new file mode 100644
index 0000000..3b6cae0
--- /dev/null
+++ b/frontend/src/socket/client.spec.ts
@@ -0,0 +1,184 @@
+import { describe, it, expect, beforeEach, vi } from 'vitest'
+import { setActivePinia, createPinia } from 'pinia'
+
+import { useAuthStore } from '@/stores/auth'
+import { socketClient } from './client'
+
+describe('socketClient', () => {
+  beforeEach(() => {
+    setActivePinia(createPinia())
+    // Reset socket client state
+    socketClient.disconnect()
+  })
+
+  describe('initial state', () => {
+    it('starts disconnected', () => {
+      /**
+       * Test that socket client initializes in disconnected state.
+       *
+       * The socket should not connect until explicitly requested,
+       * to avoid unnecessary connections on pages that don't need
+       * real-time updates.
+       */
+      expect(socketClient.connectionState).toBe('disconnected')
+      expect(socketClient.isConnected).toBe(false)
+      expect(socketClient.socket).toBeNull()
+    })
+  })
+
+  describe('connect', () => {
+    it('throws error when not authenticated', async () => {
+      /**
+       * Test that connection requires authentication.
+       *
+       * The socket server requires a valid token for authentication.
+       * Attempting to connect without one should fail immediately.
+       */
+      // Auth store starts with no tokens
+      await expect(socketClient.connect()).rejects.toThrow('not authenticated')
+    })
+
+    it('requires valid token before connecting', async () => {
+      /**
+       * Test that expired tokens prevent connection.
+       *
+       * If the token is expired and refresh fails, connection
+       * should not be attempted.
+       */
+      const auth = useAuthStore()
+      // Set expired token with no refresh token
+      auth.setTokens({
+        accessToken: 'expired-token',
+        refreshToken: '',
+        expiresAt: Date.now() - 1000, // Already expired
+      })
+
+      await expect(socketClient.connect()).rejects.toThrow('not authenticated')
+    })
+  })
+
+  describe('connection state listeners', () => {
+    it('notifies listeners of state changes', () => {
+      /**
+       * Test that connection state changes are broadcast.
+       *
+       * Components need to react to connection state changes
+       * (e.g., showing reconnecting indicator).
+       */
+      const listener = vi.fn()
+      const unsubscribe = socketClient.onConnectionStateChange(listener)
+
+      // Trigger a state change by disconnecting
+      socketClient.disconnect()
+
+      expect(listener).toHaveBeenCalledWith('disconnected')
+
+      // Cleanup
+      unsubscribe()
+    })
+
+    it('unsubscribe stops notifications', () => {
+      /**
+       * Test that unsubscribe removes the listener.
+       *
+       * Components should unsubscribe when unmounting to prevent
+       * memory leaks and stale callbacks.
+       */
+      const listener = vi.fn()
+      const unsubscribe = socketClient.onConnectionStateChange(listener)
+
+      // Unsubscribe
+      unsubscribe()
+
+      // Clear previous calls
+      listener.mockClear()
+
+      // Trigger a state change
+      socketClient.disconnect()
+
+      // Listener should not be called after unsubscribe
+      expect(listener).not.toHaveBeenCalled()
+    })
+
+    it('supports multiple listeners', () => {
+      /**
+       * Test that multiple listeners can subscribe.
+       *
+       * Different components may need to track connection state
+       * independently.
+       */
+      const listener1 = vi.fn()
+      const listener2 = vi.fn()
+
+      const unsub1 = socketClient.onConnectionStateChange(listener1)
+      const unsub2 = socketClient.onConnectionStateChange(listener2)
+
+      socketClient.disconnect()
+
+      expect(listener1).toHaveBeenCalledWith('disconnected')
+      expect(listener2).toHaveBeenCalledWith('disconnected')
+
+      // Cleanup
+      unsub1()
+      unsub2()
+    })
+  })
+
+  describe('disconnect', () => {
+    it('sets state to disconnected', () => {
+      /**
+       * Test that disconnect updates the connection state.
+       *
+       * After disconnecting, the state should reflect that
+       * we're no longer connected.
+       */
+      socketClient.disconnect()
+
+      expect(socketClient.connectionState).toBe('disconnected')
+      expect(socketClient.isConnected).toBe(false)
+    })
+
+    it('clears socket reference', () => {
+      /**
+       * Test that disconnect clears the socket.
+       *
+       * After disconnecting, the socket reference should be null
+       * to prevent accidental use of a dead connection.
+       */
+      socketClient.disconnect()
+
+      expect(socketClient.socket).toBeNull()
+    })
+  })
+
+  describe('helper methods exist', () => {
+    it('has all game action helpers', () => {
+      /**
+       * Test that all game action helper methods exist.
+       *
+       * These helpers provide a clean API for common game operations
+       * without needing to know the exact event names.
+       */
+      expect(typeof socketClient.joinGame).toBe('function')
+      expect(typeof socketClient.sendAction).toBe('function')
+      expect(typeof socketClient.resign).toBe('function')
+      expect(typeof socketClient.spectate).toBe('function')
+      expect(typeof socketClient.leaveSpectate).toBe('function')
+    })
+
+    it('has all event subscription helpers', () => {
+      /**
+       * Test that all event subscription helper methods exist.
+       *
+       * These helpers provide typed subscriptions to server events
+       * with automatic cleanup via returned unsubscribe functions.
+       */
+      expect(typeof socketClient.onGameState).toBe('function')
+      expect(typeof socketClient.onActionResult).toBe('function')
+      expect(typeof socketClient.onGameError).toBe('function')
+      expect(typeof socketClient.onGameOver).toBe('function')
+      expect(typeof socketClient.onOpponentConnected).toBe('function')
+      expect(typeof socketClient.onTurnTimeoutWarning).toBe('function')
+    })
+  })
+})
diff --git a/frontend/src/socket/client.ts b/frontend/src/socket/client.ts
new file mode 100644
index 0000000..7956216
--- /dev/null
+++ b/frontend/src/socket/client.ts
@@ -0,0 +1,284 @@
+/**
+ * Socket.IO client manager for real-time game communication.
+ *
+ * Provides a singleton connection manager with:
+ * - Automatic authentication via token
+ * - Reconnection with exponential backoff
+ * - Typed event emitters for the game namespace
+ */
+import { io, Socket } from 'socket.io-client'
+
+import { config } from '@/config'
+import { useAuthStore } from '@/stores/auth'
+import type { ClientToServerEvents, ServerToClientEvents } from './types'
+
+type TypedSocket = Socket<ServerToClientEvents, ClientToServerEvents>
+
+export type ConnectionState = 'disconnected' | 'connecting' | 'connected' | 'reconnecting'
+
+export interface SocketClientOptions {
+  /** Auto-connect on creation (default: false) */
+  autoConnect?: boolean
+  /** Namespace to connect to (default: '/game') */
+  namespace?: string
+}
+
+/**
+ * Socket.IO client manager.
+ *
+ * Use `socketClient.connect()` to establish connection.
+ * Use `socketClient.socket` to access the raw socket for event handling.
+ */
+class SocketClient {
+  private _socket: TypedSocket | null = null
+  private _connectionState: ConnectionState = 'disconnected'
+  private _namespace: string = '/game'
+
+  // Event listeners for connection state changes
+  private connectionListeners: Set<(state: ConnectionState) => void> = new Set()
+
+  /**
+   * Get the current connection state.
+   */
+  get connectionState(): ConnectionState {
+    return this._connectionState
+  }
+
+  /**
+   * Get the raw socket instance.
+   *
+   * Returns null if not connected.
+   */
+  get socket(): TypedSocket | null {
+    return this._socket
+  }
+
+  /**
+   * Check if currently connected.
+   */
+  get isConnected(): boolean {
+    return this._connectionState === 'connected'
+  }
+
+  /**
+   * Connect to the Socket.IO server.
+   *
+   * Authenticates using the current access token from auth store.
+   */
+  async connect(options: SocketClientOptions = {}): Promise<void> {
+    const { autoConnect = true, namespace = '/game' } = options
+    this._namespace = namespace
+
+    // Don't reconnect if already connected
+    if (this._socket?.connected) {
+      return
+    }
+
+    // Disconnect existing socket if any
+    if (this._socket) {
+      this._socket.disconnect()
+      this._socket = null
+    }
+
+    const auth = useAuthStore()
+    const token = await auth.getValidToken()
+
+    if (!token) {
+      throw new Error('Cannot connect: not authenticated')
+    }
+
+    this.setConnectionState('connecting')
+
+    const socketUrl = `${config.wsUrl}${namespace}`
+
+    this._socket = io(socketUrl, {
+      auth: { token },
+      autoConnect,
+      reconnection: true,
+      reconnectionAttempts: 10,
+      reconnectionDelay: 1000,
+      reconnectionDelayMax: 30000,
+      timeout: 20000,
+      transports: ['websocket', 'polling'],
+    }) as TypedSocket
+
+    this.setupEventHandlers()
+
+    // Wait for connection or error
+    return new Promise((resolve, reject) => {
+      const timeout = setTimeout(() => {
+        reject(new Error('Connection timeout'))
+      }, 20000)
+
+      this._socket!.once('connect', () => {
+        clearTimeout(timeout)
+        resolve()
+      })
+
+      this._socket!.once('connect_error', (error) => {
+        clearTimeout(timeout)
+        reject(error)
+      })
+    })
+  }
+
+  /**
+   * Disconnect from the server.
+   */
+  disconnect(): void {
+    if (this._socket) {
+      this._socket.disconnect()
+      this._socket = null
+    }
+    this.setConnectionState('disconnected')
+  }
+
+  /**
+   * Set up internal event handlers for connection management.
+   */
+  private setupEventHandlers(): void {
+    if (!this._socket) return
+
+    this._socket.on('connect', () => {
+      this.setConnectionState('connected')
+    })
+
+    this._socket.on('disconnect', (reason) => {
+      if (reason === 'io server disconnect') {
+        // Server initiated disconnect - don't auto-reconnect
+        this.setConnectionState('disconnected')
+      } else {
+        // Client-side disconnect or network issue - will auto-reconnect
+        this.setConnectionState('reconnecting')
+      }
+    })
+
+    this._socket.io.on('reconnect_attempt', () => {
+      this.setConnectionState('reconnecting')
+    })
+
+    this._socket.io.on('reconnect', () => {
+      this.setConnectionState('connected')
+    })
+
+    this._socket.io.on('reconnect_failed', () => {
+      this.setConnectionState('disconnected')
+    })
+  }
+
+  /**
+   * Update connection state and notify listeners.
+   */
+  private setConnectionState(state: ConnectionState): void {
+    this._connectionState = state
+    this.connectionListeners.forEach(listener => listener(state))
+  }
+
+  /**
+   * Subscribe to connection state changes.
+   *
+   * @returns Unsubscribe function
+   */
+  onConnectionStateChange(listener: (state: ConnectionState) => void): () => void {
+    this.connectionListeners.add(listener)
+    return () => this.connectionListeners.delete(listener)
+  }
+
+  // ============================================
+  // Game Event Helpers
+  // ============================================
+
+  /**
+   * Join a game room.
+   */
+  joinGame(gameId: string): void {
+    this._socket?.emit('game:join', { game_id: gameId })
+  }
+
+  /**
+   * Send a game action.
+   */
+  sendAction(action: ClientToServerEvents['game:action'] extends (data: infer T) => void ? T : never): void {
+    this._socket?.emit('game:action', action)
+  }
+
+  /**
+   * Resign from the current game.
+   */
+  resign(gameId: string): void {
+    this._socket?.emit('game:resign', { game_id: gameId })
+  }
+
+  /**
+   * Join as spectator.
+   */
+  spectate(gameId: string): void {
+    this._socket?.emit('game:spectate', { game_id: gameId })
+  }
+
+  /**
+   * Leave spectator mode.
+   */
+  leaveSpectate(gameId: string): void {
+    this._socket?.emit('game:leave_spectate', { game_id: gameId })
+  }
+
+  // ============================================
+  // Event Subscription Helpers
+  // ============================================
+
+  /**
+   * Subscribe to game state updates.
+   */
+  onGameState(handler: ServerToClientEvents['game:state']): () => void {
+    this._socket?.on('game:state', handler)
+    return () => this._socket?.off('game:state', handler)
+  }
+
+  /**
+   * Subscribe to action results.
+   */
+  onActionResult(handler: ServerToClientEvents['game:action_result']): () => void {
+    this._socket?.on('game:action_result', handler)
+    return () => this._socket?.off('game:action_result', handler)
+  }
+
+  /**
+   * Subscribe to game errors.
+   */
+  onGameError(handler: ServerToClientEvents['game:error']): () => void {
+    this._socket?.on('game:error', handler)
+    return () => this._socket?.off('game:error', handler)
+  }
+
+  /**
+   * Subscribe to game over events.
+   */
+  onGameOver(handler: ServerToClientEvents['game:game_over']): () => void {
+    this._socket?.on('game:game_over', handler)
+    return () => this._socket?.off('game:game_over', handler)
+  }
+
+  /**
+   * Subscribe to opponent connection status.
+   */
+  onOpponentConnected(handler: ServerToClientEvents['game:opponent_connected']): () => void {
+    this._socket?.on('game:opponent_connected', handler)
+    return () => this._socket?.off('game:opponent_connected', handler)
+  }
+
+  /**
+   * Subscribe to turn timeout warnings.
+   */
+  onTurnTimeoutWarning(handler: ServerToClientEvents['game:turn_timeout_warning']): () => void {
+    this._socket?.on('game:turn_timeout_warning', handler)
+    return () => this._socket?.off('game:turn_timeout_warning', handler)
+  }
+}
+
+/**
+ * Singleton socket client instance.
+ */
+export const socketClient = new SocketClient()
+
+export default socketClient
diff --git a/frontend/src/socket/index.ts b/frontend/src/socket/index.ts
new file mode 100644
index 0000000..6669c73
--- /dev/null
+++ b/frontend/src/socket/index.ts
@@ -0,0 +1,29 @@
+/**
+ * Socket.IO module exports.
+ */
+export { socketClient, default } from './client'
+export type { ConnectionState, SocketClientOptions } from './client'
+export type {
+  // Event types
+  ClientToServerEvents,
+  ServerToClientEvents,
+  // Game types
+  GameState,
+  PlayerState,
+  OpponentState,
+  Card,
+  CardInPlay,
+  Attack,
+  StatusCondition,
+  // Action types
+  GameAction,
+  GameActionType,
+  ActionResult,
+  ForcedAction,
+  // Other types
+  TurnPhase,
+  GameError,
+  GameOverData,
+  GameOverReason,
+  GameStats,
+} from './types'
diff --git a/frontend/src/socket/types.ts b/frontend/src/socket/types.ts
new file mode 100644
index 0000000..3f7a636
--- /dev/null
+++ b/frontend/src/socket/types.ts
@@ -0,0 +1,225 @@
+/**
+ * Socket.IO types for the game namespace.
+ *
+ * Based on backend WebSocket documentation in backend/app/socketio/
+ */
+
+// ============================================
+// Client -> Server Events
+// ============================================
+
+export interface ClientToServerEvents {
+  /** Join or rejoin a game room */
+  'game:join': (data: { game_id: string }) => void
+  /** Execute a game action */
+  'game:action': (data: GameAction) => void
+  /** Resign from the current game */
+  'game:resign': (data: { game_id: string }) => void
+  /** Join as spectator */
+  'game:spectate': (data: { game_id: string }) => void
+  /** Leave spectator mode */
+  'game:leave_spectate': (data: { game_id: string }) => void
+}
+
+// ============================================
+// Server -> Client Events
+// ============================================
+
+export interface ServerToClientEvents {
+  /** Full game state update (visibility filtered per player) */
+  'game:state': (state: GameState) => void
+  /** Result of a player action */
+  'game:action_result': (result: ActionResult) => void
+  /** Error notification */
+  'game:error': (error: GameError) => void
+  /** Turn timer warning */
+  'game:turn_timeout_warning': (data: { remaining_seconds: number }) => void
+  /** Game has ended */
+  'game:game_over': (data: GameOverData) => void
+  /** Opponent connection status changed */
+  'game:opponent_connected': (data: { connected: boolean }) => void
+  /** Auto-reconnected to game */
+  'game:reconnected': (data: { game_id: string; state: GameState }) => void
+  /** Spectator count update */
+  'game:spectator_count': (data: { count: number }) => void
+}
+
+// ============================================
+// Game Action Types
+// ============================================
+
+export type GameActionType =
+  | 'play_pokemon'
+  | 'attach_energy'
+  | 'play_trainer'
+  | 'attack'
+  | 'retreat'
+  | 'use_ability'
+  | 'select_prize'
+  | 'select_new_active'
+  | 'end_turn'
+
+export interface GameAction {
+  type: GameActionType
+  /** Card ID being played (for play actions) */
+  card_id?: string
+  /** Target card/zone ID */
+  target_id?: string
+  /** Attack index (0 or 1) */
+  attack_index?: number
+  /** Additional action-specific data */
+  data?: Record<string, unknown>
+}
+
+// ============================================
+// Game State Types
+// ============================================
+
+export interface GameState {
+  game_id: string
+  turn_number: number
+  current_phase: TurnPhase
+  current_player: 'me' | 'opponent'
+  /** My visible state */
+  my_state: PlayerState
+  /** Opponent's visible state (hidden info redacted) */
+  opponent_state: OpponentState
+  /** Forced action required (e.g., select prize) */
+  forced_action?: ForcedAction
+  /** Turn timer remaining (seconds) */
+  turn_timer?: number
+}
+
+export type TurnPhase = 'draw' | 'main' | 'attack' | 'end'
+
+export interface PlayerState {
+  /** Active Pokemon (full info) */
+  active: CardInPlay | null
+  /** Bench Pokemon (up to 5) */
+  bench: (CardInPlay | null)[]
+  /** Hand cards (full info - only visible to owner) */
+  hand: Card[]
+  /** Deck count (not contents) */
+  deck_count: number
+  /** Discard pile (visible to both players) */
+  discard: Card[]
+  /** Prize cards (face down until taken) */
+  prizes: (Card | null)[]
+  /** Number of prizes remaining */
+  prizes_remaining: number
+}
+
+export interface OpponentState {
+  /** Active Pokemon (public info only) */
+  active: CardInPlay | null
+  /** Bench Pokemon */
+  bench: (CardInPlay | null)[]
+  /** Hand count only (not contents) */
+  hand_count: number
+  /** Deck count */
+  deck_count: number
+  /** Discard pile */
+  discard: Card[]
+  /** Prize count (not contents) */
+  prizes_remaining: number
+}
+
+export interface Card {
+  id: string
+  definition_id: string
+  name: string
+  card_type: 'pokemon' | 'trainer' | 'energy'
+  /** Pokemon-specific fields */
+  hp?: number
+  pokemon_type?: string
+  stage?: 'basic' | 'stage1' | 'stage2'
+  evolves_from?: string
+  attacks?: Attack[]
+  weakness?: string
+  resistance?: string
+  retreat_cost?: number
+  /** Energy-specific fields */
+  energy_type?: string
+  /** Trainer-specific fields */
+  trainer_type?: 'item' | 'supporter' | 'stadium'
+}
+
+export interface CardInPlay extends Card {
+  /** Current damage on the card */
+  damage: number
+  /** Attached energy cards */
+  attached_energy: Card[]
+  /** Status conditions */
+  status: StatusCondition[]
+  /** Can evolve this turn */
+  can_evolve: boolean
+}
+
+export interface Attack {
+  name: string
+  cost: string[]
+  damage: number
+  effect?: string
+  effect_text?: string
+}
+
+export type StatusCondition = 'poisoned' | 'burned' | 'paralyzed' | 'asleep' | 'confused'
+
+export interface ForcedAction {
+  type: 'select_prize' | 'select_new_active' | 'discard_cards'
+  /** Number of selections required */
+  count?: number
+  /** Valid target IDs */
+  valid_targets?: string[]
+  /** Reason for forced action */
+  reason?: string
+}
+
+// ============================================
+// Action Result Types
+// ============================================
+
+export interface ActionResult {
+  success: boolean
+  action_type: GameActionType
+  /** Error message if not successful */
+  message?: string
+  /** State changes that resulted */
+  changes?: StateChange[]
+}
+
+export interface StateChange {
+  type: string
+  data: Record<string, unknown>
+}
+
+// ============================================
+// Error and Game Over Types
+// ============================================
+
+export interface GameError {
+  message: string
+  code?: string
+}
+
+export interface GameOverData {
+  winner: 'me' | 'opponent' | 'draw'
+  reason: GameOverReason
+  /** Game statistics */
+  stats?: GameStats
+}
+
+export type GameOverReason =
+  | 'prizes_taken'
+  | 'no_pokemon'
+  | 'deck_out'
+  | 'resignation'
+  | 'timeout'
+  | 'disconnect'
+
+export interface GameStats {
+  turns: number
+  cards_played: number
+  damage_dealt: number
+  knockouts: number
+}