diff --git a/src/test/e2e/happy-path.test.ts b/src/test/e2e/happy-path.test.ts
new file mode 100644
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+++ b/src/test/e2e/happy-path.test.ts
@@ -0,0 +1,269 @@
+/**
+ * E2E Happy Path Tests
+ *
+ * Tests proving core dispatch/coordination flow works end-to-end
+ * using the TestHarness with mocked agents and worktrees.
+ */
+
+import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest';
+import {
+  createTestHarness,
+  SIMPLE_FIXTURE,
+  PARALLEL_FIXTURE,
+  COMPLEX_FIXTURE,
+  type TestHarness,
+} from '../index.js';
+
+describe('E2E Happy Path', () => {
+  let harness: TestHarness;
+
+  beforeEach(() => {
+    harness = createTestHarness();
+  });
+
+  afterEach(() => {
+    harness.cleanup();
+    vi.useRealTimers();
+  });
+
+  // ===========================================================================
+  // Scenario 1: Single Task Flow
+  // ===========================================================================
+
+  describe('Single task flow', () => {
+    it('completes a single task from queue to completion', async () => {
+      vi.useFakeTimers();
+      const seeded = await harness.seedFixture(SIMPLE_FIXTURE);
+      const taskAId = seeded.tasks.get('Task A')!;
+
+      // Pre-seed idle agent (required by DispatchManager before spawning new ones)
+      await harness.agentManager.spawn({
+        name: 'pool-agent',
+        taskId: 'placeholder',
+        prompt: 'placeholder',
+      });
+      await vi.runAllTimersAsync();
+      harness.clearEvents();
+
+      // Step 1: Queue task
+      await harness.dispatchManager.queue(taskAId);
+
+      // Verify task:queued event
+      const queuedEvents = harness.getEventsByType('task:queued');
+      expect(queuedEvents.length).toBe(1);
+      expect((queuedEvents[0].payload as { taskId: string }).taskId).toBe(taskAId);
+
+      // Step 2: Dispatch task
+      const dispatchResult = await harness.dispatchManager.dispatchNext();
+      expect(dispatchResult.success).toBe(true);
+      expect(dispatchResult.taskId).toBe(taskAId);
+      expect(dispatchResult.agentId).toBeDefined();
+
+      // Verify task:dispatched event
+      const dispatchedEvents = harness.getEventsByType('task:dispatched');
+      expect(dispatchedEvents.length).toBe(1);
+      expect((dispatchedEvents[0].payload as { taskId: string }).taskId).toBe(taskAId);
+
+      // Verify agent:spawned event
+      const spawnedEvents = harness.getEventsByType('agent:spawned');
+      expect(spawnedEvents.length).toBe(1);
+
+      // Step 3: Wait for agent completion
+      await vi.runAllTimersAsync();
+
+      // Verify agent:stopped event
+      const stoppedEvents = harness.getEventsByType('agent:stopped');
+      expect(stoppedEvents.length).toBe(1);
+
+      // Step 4: Mark task complete
+      await harness.dispatchManager.completeTask(taskAId);
+
+      // Verify task status in database
+      const task = await harness.taskRepository.findById(taskAId);
+      expect(task?.status).toBe('completed');
+    });
+  });
+
+  // ===========================================================================
+  // Scenario 2: Sequential Dependencies
+  // ===========================================================================
+
+  describe('Sequential dependencies', () => {
+    it('dispatches tasks in priority order (dependency ordering via task status)', async () => {
+      vi.useFakeTimers();
+      const seeded = await harness.seedFixture(SIMPLE_FIXTURE);
+      const taskAId = seeded.tasks.get('Task A')!;
+      const taskBId = seeded.tasks.get('Task B')!;
+      const taskCId = seeded.tasks.get('Task C')!;
+
+      // Pre-seed idle agent
+      await harness.agentManager.spawn({
+        name: 'pool-agent',
+        taskId: 'placeholder',
+        prompt: 'placeholder',
+      });
+      await vi.runAllTimersAsync();
+      harness.clearEvents();
+
+      // Queue all three tasks
+      await harness.dispatchManager.queue(taskAId);
+      await harness.dispatchManager.queue(taskBId);
+      await harness.dispatchManager.queue(taskCId);
+      harness.clearEvents();
+
+      // All three tasks are queued
+      const queueState = await harness.dispatchManager.getQueueState();
+      expect(queueState.queued.length).toBe(3);
+
+      // First dispatchNext: Task A (high priority) dispatches first
+      const nextTask = await harness.dispatchManager.getNextDispatchable();
+      expect(nextTask).not.toBeNull();
+      expect(nextTask!.taskId).toBe(taskAId); // High priority first
+
+      // All tasks are "ready" in current implementation (dependency loading TBD)
+      const readyTaskIds = queueState.ready.map((t) => t.taskId);
+      expect(readyTaskIds).toContain(taskAId);
+
+      // Dispatch Task A
+      const dispatchResult = await harness.dispatchManager.dispatchNext();
+      expect(dispatchResult.success).toBe(true);
+      expect(dispatchResult.taskId).toBe(taskAId);
+
+      // Wait for agent completion
+      await vi.runAllTimersAsync();
+
+      // Complete Task A
+      await harness.dispatchManager.completeTask(taskAId);
+
+      // Verify Task A removed from queue, B and C remain
+      const queueStateAfter = await harness.dispatchManager.getQueueState();
+      const remainingTaskIds = queueStateAfter.queued.map((t) => t.taskId);
+      expect(remainingTaskIds).not.toContain(taskAId);
+      expect(remainingTaskIds).toContain(taskBId);
+      expect(remainingTaskIds).toContain(taskCId);
+
+      // Task A marked completed in database
+      const taskA = await harness.taskRepository.findById(taskAId);
+      expect(taskA?.status).toBe('completed');
+    });
+  });
+
+  // ===========================================================================
+  // Scenario 3: Parallel Dispatch
+  // ===========================================================================
+
+  describe('Parallel dispatch', () => {
+    it('dispatches multiple independent tasks to multiple agents', async () => {
+      vi.useFakeTimers();
+      const seeded = await harness.seedFixture(PARALLEL_FIXTURE);
+      const taskXId = seeded.tasks.get('Task X')!;
+      const taskYId = seeded.tasks.get('Task Y')!;
+      const taskPId = seeded.tasks.get('Task P')!;
+      const taskQId = seeded.tasks.get('Task Q')!;
+
+      // Pre-seed 2 idle agents
+      await harness.agentManager.spawn({
+        name: 'pool-agent-1',
+        taskId: 'placeholder-1',
+        prompt: 'placeholder',
+      });
+      await harness.agentManager.spawn({
+        name: 'pool-agent-2',
+        taskId: 'placeholder-2',
+        prompt: 'placeholder',
+      });
+      await vi.runAllTimersAsync();
+      harness.clearEvents();
+
+      // Queue all 4 tasks
+      await harness.dispatchManager.queue(taskXId);
+      await harness.dispatchManager.queue(taskYId);
+      await harness.dispatchManager.queue(taskPId);
+      await harness.dispatchManager.queue(taskQId);
+      harness.clearEvents();
+
+      // All 4 tasks should be dispatchable (no dependencies)
+      const queueState = await harness.dispatchManager.getQueueState();
+      expect(queueState.ready.length).toBe(4);
+
+      // Dispatch first task
+      const result1 = await harness.dispatchManager.dispatchNext();
+      expect(result1.success).toBe(true);
+
+      // Dispatch second task (parallel)
+      const result2 = await harness.dispatchManager.dispatchNext();
+      expect(result2.success).toBe(true);
+
+      // Verify both agents assigned different tasks
+      expect(result1.taskId).not.toBe(result2.taskId);
+      expect(result1.agentId).not.toBe(result2.agentId);
+
+      // Both dispatches succeeded
+      const dispatchedEvents = harness.getEventsByType('task:dispatched');
+      expect(dispatchedEvents.length).toBe(2);
+    });
+  });
+
+  // ===========================================================================
+  // Scenario 4: Full Merge Flow
+  // ===========================================================================
+
+  describe('Full merge flow', () => {
+    it('queues and processes merge after task completion', async () => {
+      vi.useFakeTimers();
+      const seeded = await harness.seedFixture(SIMPLE_FIXTURE);
+      const taskAId = seeded.tasks.get('Task A')!;
+
+      // Pre-seed idle agent in MockAgentManager
+      await harness.agentManager.spawn({
+        name: 'pool-agent',
+        taskId: 'placeholder',
+        prompt: 'placeholder',
+      });
+      await vi.runAllTimersAsync();
+      harness.clearEvents();
+
+      // Queue and dispatch task
+      await harness.dispatchManager.queue(taskAId);
+      const dispatchResult = await harness.dispatchManager.dispatchNext();
+      expect(dispatchResult.success).toBe(true);
+
+      // Wait for agent completion
+      await vi.runAllTimersAsync();
+
+      // Complete task
+      await harness.dispatchManager.completeTask(taskAId);
+      harness.clearEvents();
+
+      // Create agent in database (CoordinationManager.queueMerge requires it)
+      // This bridges the gap between MockAgentManager (in-memory) and AgentRepository (database)
+      const worktreeId = `worktree-${taskAId.slice(0, 8)}`;
+      const agent = await harness.agentRepository.create({
+        name: `agent-${taskAId.slice(0, 6)}`,
+        taskId: taskAId,
+        worktreeId,
+        status: 'idle',
+      });
+
+      // Create worktree for merge
+      await harness.worktreeManager.create(worktreeId, `feature-${taskAId.slice(0, 6)}`);
+
+      // Queue merge
+      await harness.coordinationManager.queueMerge(taskAId);
+
+      // Verify merge:queued event
+      const mergeQueuedEvents = harness.getEventsByType('merge:queued');
+      expect(mergeQueuedEvents.length).toBe(1);
+
+      // Process merges
+      const mergeResults = await harness.coordinationManager.processMerges('main');
+      expect(mergeResults.length).toBe(1);
+      expect(mergeResults[0].taskId).toBe(taskAId);
+      expect(mergeResults[0].success).toBe(true);
+
+      // Verify merge:completed event
+      const mergeCompletedEvents = harness.getEventsByType('merge:completed');
+      expect(mergeCompletedEvents.length).toBe(1);
+    });
+  });
+});