diff --git a/src/test/harness.ts b/src/test/harness.ts
new file mode 100644
index 0000000..c978588
--- /dev/null
+++ b/src/test/harness.ts
@@ -0,0 +1,291 @@
+/**
+ * Test Harness for E2E Testing
+ *
+ * Wires up the full system with mocks for E2E testing.
+ * Uses real managers (DispatchManager, CoordinationManager) with
+ * MockAgentManager and MockWorktreeManager for isolation.
+ */
+
+import { randomUUID } from 'crypto';
+import type { DrizzleDatabase } from '../db/index.js';
+import type { EventBus, DomainEvent } from '../events/types.js';
+import { EventEmitterBus } from '../events/bus.js';
+import type { AgentManager } from '../agent/types.js';
+import { MockAgentManager, type MockAgentScenario } from '../agent/mock-manager.js';
+import type { WorktreeManager, Worktree, WorktreeDiff, MergeResult } from '../git/types.js';
+import type { DispatchManager } from '../dispatch/types.js';
+import { DefaultDispatchManager } from '../dispatch/manager.js';
+import type { CoordinationManager } from '../coordination/types.js';
+import { DefaultCoordinationManager } from '../coordination/manager.js';
+import type { TaskRepository } from '../db/repositories/task-repository.js';
+import type { MessageRepository } from '../db/repositories/message-repository.js';
+import type { AgentRepository } from '../db/repositories/agent-repository.js';
+import {
+  DrizzleTaskRepository,
+  DrizzleMessageRepository,
+  DrizzleAgentRepository,
+} from '../db/repositories/drizzle/index.js';
+import { createTestDatabase } from '../db/repositories/drizzle/test-helpers.js';
+import {
+  seedFixture,
+  type InitiativeFixture,
+  type SeededFixture,
+} from './fixtures.js';
+
+// =============================================================================
+// MockWorktreeManager
+// =============================================================================
+
+/**
+ * Simple in-memory WorktreeManager for testing.
+ * Creates fake worktrees without actual git operations.
+ */
+export class MockWorktreeManager implements WorktreeManager {
+  private worktrees: Map<string, Worktree> = new Map();
+  private mergeResults: Map<string, MergeResult> = new Map();
+
+  /**
+   * Set a custom merge result for a specific worktree.
+   * Used to test conflict scenarios.
+   */
+  setMergeResult(worktreeId: string, result: MergeResult): void {
+    this.mergeResults.set(worktreeId, result);
+  }
+
+  async create(id: string, branch: string, baseBranch?: string): Promise<Worktree> {
+    const worktree: Worktree = {
+      id,
+      branch,
+      path: `/tmp/test-worktrees/${id}`,
+      isMainWorktree: false,
+    };
+    this.worktrees.set(id, worktree);
+    return worktree;
+  }
+
+  async remove(id: string): Promise<void> {
+    if (!this.worktrees.has(id)) {
+      throw new Error(`Worktree not found: ${id}`);
+    }
+    this.worktrees.delete(id);
+    this.mergeResults.delete(id);
+  }
+
+  async list(): Promise<Worktree[]> {
+    return Array.from(this.worktrees.values());
+  }
+
+  async get(id: string): Promise<Worktree | null> {
+    return this.worktrees.get(id) ?? null;
+  }
+
+  async diff(id: string): Promise<WorktreeDiff> {
+    if (!this.worktrees.has(id)) {
+      throw new Error(`Worktree not found: ${id}`);
+    }
+    return {
+      files: [],
+      summary: 'No changes (mock)',
+    };
+  }
+
+  async merge(id: string, targetBranch: string): Promise<MergeResult> {
+    if (!this.worktrees.has(id)) {
+      throw new Error(`Worktree not found: ${id}`);
+    }
+
+    // Return custom result if set, otherwise success
+    const customResult = this.mergeResults.get(id);
+    if (customResult) {
+      return customResult;
+    }
+
+    return {
+      success: true,
+      message: `Merged ${id} into ${targetBranch} (mock)`,
+    };
+  }
+
+  /**
+   * Clear all worktrees.
+   * Useful for test cleanup.
+   */
+  clear(): void {
+    this.worktrees.clear();
+    this.mergeResults.clear();
+  }
+}
+
+// =============================================================================
+// CapturingEventBus
+// =============================================================================
+
+/**
+ * EventBus wrapper that captures all emitted events.
+ * Extends EventEmitterBus with event capture functionality.
+ */
+export class CapturingEventBus extends EventEmitterBus {
+  /** All emitted events */
+  emittedEvents: DomainEvent[] = [];
+
+  emit<T extends DomainEvent>(event: T): void {
+    this.emittedEvents.push(event);
+    super.emit(event);
+  }
+
+  /**
+   * Get events by type.
+   */
+  getEventsByType(type: string): DomainEvent[] {
+    return this.emittedEvents.filter((e) => e.type === type);
+  }
+
+  /**
+   * Clear captured events.
+   */
+  clearEvents(): void {
+    this.emittedEvents = [];
+  }
+}
+
+// =============================================================================
+// TestHarness Interface
+// =============================================================================
+
+/**
+ * Test harness for E2E testing.
+ * Provides access to all system components and helper methods.
+ */
+export interface TestHarness {
+  // Core components
+  /** In-memory SQLite database */
+  db: DrizzleDatabase;
+  /** Event bus with event capture */
+  eventBus: CapturingEventBus;
+  /** Mock agent manager */
+  agentManager: MockAgentManager;
+  /** Mock worktree manager */
+  worktreeManager: MockWorktreeManager;
+  /** Real dispatch manager wired to mocks */
+  dispatchManager: DispatchManager;
+  /** Real coordination manager wired to mocks */
+  coordinationManager: CoordinationManager;
+
+  // Repositories
+  /** Task repository */
+  taskRepository: TaskRepository;
+  /** Message repository */
+  messageRepository: MessageRepository;
+  /** Agent repository */
+  agentRepository: AgentRepository;
+
+  // Helpers
+  /**
+   * Seed a fixture into the database.
+   */
+  seedFixture(fixture: InitiativeFixture): Promise<SeededFixture>;
+
+  /**
+   * Set scenario for a specific agent name.
+   */
+  setAgentScenario(agentName: string, scenario: MockAgentScenario): void;
+
+  /**
+   * Get events by type.
+   */
+  getEventsByType(type: string): DomainEvent[];
+
+  /**
+   * Clear all captured events.
+   */
+  clearEvents(): void;
+
+  /**
+   * Clean up all resources.
+   */
+  cleanup(): void;
+}
+
+// =============================================================================
+// createTestHarness Factory
+// =============================================================================
+
+/**
+ * Create a fully wired test harness for E2E testing.
+ *
+ * Wires:
+ * - In-memory SQLite database
+ * - CapturingEventBus (captures all events)
+ * - MockAgentManager (simulates agent behavior)
+ * - MockWorktreeManager (fake worktrees)
+ * - Real DefaultDispatchManager (with mock agent manager)
+ * - Real DefaultCoordinationManager (with mock worktree manager)
+ * - All repositories (Drizzle implementations)
+ */
+export function createTestHarness(): TestHarness {
+  // Create database
+  const db = createTestDatabase();
+
+  // Create event bus with capture
+  const eventBus = new CapturingEventBus();
+
+  // Create mock managers
+  const agentManager = new MockAgentManager({ eventBus });
+  const worktreeManager = new MockWorktreeManager();
+
+  // Create repositories
+  const taskRepository = new DrizzleTaskRepository(db);
+  const messageRepository = new DrizzleMessageRepository(db);
+  const agentRepository = new DrizzleAgentRepository(db);
+
+  // Create real managers wired to mocks
+  const dispatchManager = new DefaultDispatchManager(
+    taskRepository,
+    messageRepository,
+    agentManager,
+    eventBus
+  );
+
+  const coordinationManager = new DefaultCoordinationManager(
+    worktreeManager,
+    taskRepository,
+    agentRepository,
+    messageRepository,
+    eventBus
+  );
+
+  // Build harness
+  const harness: TestHarness = {
+    // Core components
+    db,
+    eventBus,
+    agentManager,
+    worktreeManager,
+    dispatchManager,
+    coordinationManager,
+
+    // Repositories
+    taskRepository,
+    messageRepository,
+    agentRepository,
+
+    // Helpers
+    seedFixture: (fixture: InitiativeFixture) => seedFixture(db, fixture),
+
+    setAgentScenario: (agentName: string, scenario: MockAgentScenario) => {
+      agentManager.setScenario(agentName, scenario);
+    },
+
+    getEventsByType: (type: string) => eventBus.getEventsByType(type),
+
+    clearEvents: () => eventBus.clearEvents(),
+
+    cleanup: () => {
+      agentManager.clear();
+      worktreeManager.clear();
+      eventBus.clearEvents();
+    },
+  };
+
+  return harness;
+}
diff --git a/src/test/index.ts b/src/test/index.ts
new file mode 100644
index 0000000..31c4e21
--- /dev/null
+++ b/src/test/index.ts
@@ -0,0 +1,26 @@
+/**
+ * Test Module
+ *
+ * Provides test harness and fixtures for E2E testing.
+ */
+
+// Fixture helpers
+export {
+  seedFixture,
+  type TaskFixture,
+  type PlanFixture,
+  type PhaseFixture,
+  type InitiativeFixture,
+  type SeededFixture,
+  SIMPLE_FIXTURE,
+  PARALLEL_FIXTURE,
+  COMPLEX_FIXTURE,
+} from './fixtures.js';
+
+// Test harness
+export {
+  createTestHarness,
+  MockWorktreeManager,
+  CapturingEventBus,
+  type TestHarness,
+} from './harness.js';