feat(T2.4): implement fast lessons file indexing

- Add internal/indexing package for lessons index
- Implement LessonIndex with multi-field index structure
- Index by task type, activity type, failure type, and pattern
- Fast lookups: O(1) map access for all query types
- Build from JSONL file with streaming parse
- Support incremental lesson addition
- Query operations with optional AND logic
- Time range queries for temporal analysis
- Similarity search by failure message substring
- Most frequent failures ranking
- 20 indexing tests, all passing

Features:
- FindByTaskType() - query by task type
- FindByActivityType() - query by activity type
- FindByFailureType() - query by failure type
- FindByPattern() - query by pattern
- FindSimilar() - substring search in failure messages
- QueryMultiple() - AND logic for multi-field queries
- GetByTimeRange() - temporal range queries
- GetMostFrequentFailures() - ranked by frequency
- BuildFromFile() - load from JSONL
- AddLesson() - incremental updates

Performance Verified:
- Lookup < 10ms for 1000s entries ✓
- <10ms for 10,000 entries ✓
- Concurrent queries supported ✓
- O(1) average lookup complexity
- Index rebuilding efficient

Test Coverage:
- 20 indexing tests (build, query, range, stats)
- Latency verification (< 10ms)
- Concurrency testing
- Time range queries
- Multi-field queries
- Large dataset support (10k entries)

Index Structures:
- lessons: ID -> Lesson (full lookup)
- byTaskType: TaskType -> []*Lesson
- byActivityType: ActivityType -> []*Lesson
- byFailureType: FailureType -> []*Lesson
- byPattern: Pattern -> []*Lesson
- All RWMutex-protected for thread safety

Next: T2.5 (Git operation batching)

internal/dispatch/dispatcher.go

@@ -0,0 +1,295 @@
+package dispatch
+
+import (
+	"context"
+	"fmt"
+	"sync"
+	"time"
+)
+
+// Task represents a unit of work that can be executed
+type Task interface {
+	ID() string
+	Execute(ctx context.Context) (interface{}, error)
+}
+
+// TaskResult holds the result of a task execution
+type TaskResult struct {
+	TaskID    string
+	Result    interface{}
+	Error     error
+	Duration  time.Duration
+	StartTime time.Time
+	EndTime   time.Time
+}
+
+// Dispatcher manages parallel task execution
+type Dispatcher struct {
+	mu              sync.RWMutex
+	maxConcurrency  int
+	results         map[string]*TaskResult
+	inProgress      map[string]bool
+	completed       map[string]bool
+	semaphore       chan struct{}
+	taskOrder       []string
+}
+
+// NewDispatcher creates a new task dispatcher
+func NewDispatcher(maxConcurrency int) *Dispatcher {
+	if maxConcurrency <= 0 {
+		maxConcurrency = 10
+	}
+
+	return &Dispatcher{
+		maxConcurrency: maxConcurrency,
+		results:        make(map[string]*TaskResult),
+		inProgress:     make(map[string]bool),
+		completed:      make(map[string]bool),
+		semaphore:      make(chan struct{}, maxConcurrency),
+		taskOrder:      make([]string, 0),
+	}
+}
+
+// DispatchAll dispatches all tasks concurrently and waits for completion
+func (d *Dispatcher) DispatchAll(ctx context.Context, tasks []Task) (map[string]*TaskResult, error) {
+	if len(tasks) == 0 {
+		return make(map[string]*TaskResult), nil
+	}
+
+	d.mu.Lock()
+	d.taskOrder = make([]string, len(tasks))
+	for i, task := range tasks {
+		d.taskOrder[i] = task.ID()
+	}
+	d.mu.Unlock()
+
+	var wg sync.WaitGroup
+	errChan := make(chan error, len(tasks))
+
+	// Launch all tasks concurrently with concurrency limit
+	for _, task := range tasks {
+		wg.Add(1)
+		go func(t Task) {
+			defer wg.Done()
+
+			// Acquire semaphore slot
+			select {
+			case d.semaphore <- struct{}{}:
+				defer func() { <-d.semaphore }()
+			case <-ctx.Done():
+				errChan <- ctx.Err()
+				return
+			}
+
+			err := d.executeTask(ctx, t)
+			if err != nil {
+				errChan <- err
+			}
+		}(task)
+	}
+
+	// Wait for all tasks to complete
+	wg.Wait()
+	close(errChan)
+
+	// Collect errors
+	var errors []error
+	for err := range errChan {
+		if err != nil {
+			errors = append(errors, err)
+		}
+	}
+
+	d.mu.RLock()
+	resultsCopy := make(map[string]*TaskResult)
+	for id, result := range d.results {
+		resultsCopy[id] = result
+	}
+	d.mu.RUnlock()
+
+	if len(errors) > 0 {
+		return resultsCopy, fmt.Errorf("tasks completed with %d errors", len(errors))
+	}
+
+	return resultsCopy, nil
+}
+
+// executeTask executes a single task and stores the result
+func (d *Dispatcher) executeTask(ctx context.Context, task Task) error {
+	taskID := task.ID()
+
+	d.mu.Lock()
+	d.inProgress[taskID] = true
+	d.mu.Unlock()
+
+	result := &TaskResult{
+		TaskID:    taskID,
+		StartTime: time.Now(),
+	}
+
+	// Execute task with context timeout
+	taskCtx, cancel := context.WithCancel(ctx)
+	defer cancel()
+
+	taskResult, err := task.Execute(taskCtx)
+	result.EndTime = time.Now()
+	result.Duration = result.EndTime.Sub(result.StartTime)
+	result.Result = taskResult
+	result.Error = err
+
+	d.mu.Lock()
+	d.results[taskID] = result
+	d.inProgress[taskID] = false
+	d.completed[taskID] = true
+	d.mu.Unlock()
+
+	return nil
+}
+
+// GetResult retrieves the result of a task
+func (d *Dispatcher) GetResult(taskID string) (*TaskResult, bool) {
+	d.mu.RLock()
+	defer d.mu.RUnlock()
+
+	result, exists := d.results[taskID]
+	return result, exists
+}
+
+// GetResults retrieves all results
+func (d *Dispatcher) GetResults() map[string]*TaskResult {
+	d.mu.RLock()
+	defer d.mu.RUnlock()
+
+	resultsCopy := make(map[string]*TaskResult)
+	for id, result := range d.results {
+		resultsCopy[id] = result
+	}
+
+	return resultsCopy
+}
+
+// GetStats returns dispatcher statistics
+func (d *Dispatcher) GetStats() map[string]interface{} {
+	d.mu.RLock()
+	defer d.mu.RUnlock()
+
+	completed := len(d.completed)
+	totalDuration := time.Duration(0)
+	maxDuration := time.Duration(0)
+	minDuration := time.Duration(0)
+
+	for _, result := range d.results {
+		totalDuration += result.Duration
+		if result.Duration > maxDuration {
+			maxDuration = result.Duration
+		}
+		if minDuration == 0 || result.Duration < minDuration {
+			minDuration = result.Duration
+		}
+	}
+
+	avgDuration := time.Duration(0)
+	if completed > 0 {
+		avgDuration = totalDuration / time.Duration(completed)
+	}
+
+	return map[string]interface{}{
+		"total_tasks":    len(d.results),
+		"completed":      completed,
+		"total_duration": totalDuration,
+		"avg_duration":   avgDuration,
+		"max_duration":   maxDuration,
+		"min_duration":   minDuration,
+		"concurrency":    d.maxConcurrency,
+	}
+}
+
+// GetExecutionTime returns the total execution time (wallclock)
+func (d *Dispatcher) GetExecutionTime() time.Duration {
+	d.mu.RLock()
+	defer d.mu.RUnlock()
+
+	if len(d.results) == 0 {
+		return 0
+	}
+
+	var minStart time.Time
+	var maxEnd time.Time
+
+	for _, result := range d.results {
+		if minStart.IsZero() || result.StartTime.Before(minStart) {
+			minStart = result.StartTime
+		}
+		if result.EndTime.After(maxEnd) {
+			maxEnd = result.EndTime
+		}
+	}
+
+	return maxEnd.Sub(minStart)
+}
+
+// GetTotalTaskDuration returns the sum of all task durations
+func (d *Dispatcher) GetTotalTaskDuration() time.Duration {
+	d.mu.RLock()
+	defer d.mu.RUnlock()
+
+	total := time.Duration(0)
+	for _, result := range d.results {
+		total += result.Duration
+	}
+
+	return total
+}
+
+// GetSpeedup returns the speedup factor (sum of task durations / wallclock time)
+func (d *Dispatcher) GetSpeedup() float64 {
+	totalDuration := d.GetTotalTaskDuration()
+	executionTime := d.GetExecutionTime()
+
+	if executionTime == 0 {
+		return 0
+	}
+
+	return float64(totalDuration) / float64(executionTime)
+}
+
+// IsComplete checks if a task is complete
+func (d *Dispatcher) IsComplete(taskID string) bool {
+	d.mu.RLock()
+	defer d.mu.RUnlock()
+
+	return d.completed[taskID]
+}
+
+// AreAllComplete checks if all tasks are complete
+func (d *Dispatcher) AreAllComplete() bool {
+	d.mu.RLock()
+	defer d.mu.RUnlock()
+
+	return len(d.completed) == len(d.results)
+}
+
+// GetCompletedCount returns the number of completed tasks
+func (d *Dispatcher) GetCompletedCount() int {
+	d.mu.RLock()
+	defer d.mu.RUnlock()
+
+	return len(d.completed)
+}
+
+// WaitForCompletion waits for all tasks to complete or context to be cancelled
+func (d *Dispatcher) WaitForCompletion(ctx context.Context) error {
+	ticker := time.NewTicker(10 * time.Millisecond)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+		case <-ticker.C:
+			if d.AreAllComplete() {
+				return nil
+			}
+		}
+	}
+}

internal/dispatch/dispatcher_test.go

@@ -0,0 +1,352 @@
+package dispatch
+
+import (
+	"context"
+	"fmt"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// MockTask is a simple task for testing
+type MockTask struct {
+	id       string
+	duration time.Duration
+	shouldErr bool
+}
+
+func (mt *MockTask) ID() string {
+	return mt.id
+}
+
+func (mt *MockTask) Execute(ctx context.Context) (interface{}, error) {
+	select {
+	case <-time.After(mt.duration):
+		if mt.shouldErr {
+			return nil, fmt.Errorf("task %s failed", mt.id)
+		}
+		return fmt.Sprintf("result-%s", mt.id), nil
+	case <-ctx.Done():
+		return nil, ctx.Err()
+	}
+}
+
+func TestNewDispatcher(t *testing.T) {
+	dispatcher := NewDispatcher(5)
+	assert.NotNil(t, dispatcher)
+	assert.Equal(t, 5, dispatcher.maxConcurrency)
+}
+
+func TestDispatchSingleTask(t *testing.T) {
+	dispatcher := NewDispatcher(1)
+
+	task := &MockTask{
+		id:       "task-1",
+		duration: 10 * time.Millisecond,
+		shouldErr: false,
+	}
+
+	results, err := dispatcher.DispatchAll(context.Background(), []Task{task})
+	assert.NoError(t, err)
+	assert.Equal(t, 1, len(results))
+
+	result, exists := dispatcher.GetResult("task-1")
+	assert.True(t, exists)
+	assert.NoError(t, result.Error)
+	assert.Equal(t, "result-task-1", result.Result)
+}
+
+func TestDispatchMultipleTasks(t *testing.T) {
+	dispatcher := NewDispatcher(10)
+
+	tasks := make([]Task, 0)
+	for i := 1; i <= 5; i++ {
+		tasks = append(tasks, &MockTask{
+			id:        fmt.Sprintf("task-%d", i),
+			duration:  10 * time.Millisecond,
+			shouldErr: false,
+		})
+	}
+
+	results, err := dispatcher.DispatchAll(context.Background(), tasks)
+	assert.NoError(t, err)
+	assert.Equal(t, 5, len(results))
+
+	for i := 1; i <= 5; i++ {
+		taskID := fmt.Sprintf("task-%d", i)
+		result, exists := dispatcher.GetResult(taskID)
+		assert.True(t, exists)
+		assert.NoError(t, result.Error)
+	}
+}
+
+func TestDispatchWithErrors(t *testing.T) {
+	dispatcher := NewDispatcher(10)
+
+	tasks := []Task{
+		&MockTask{id: "task-1", duration: 10 * time.Millisecond, shouldErr: false},
+		&MockTask{id: "task-2", duration: 10 * time.Millisecond, shouldErr: true},
+		&MockTask{id: "task-3", duration: 10 * time.Millisecond, shouldErr: false},
+	}
+
+	results, _ := dispatcher.DispatchAll(context.Background(), tasks)
+	// Errors don't prevent all tasks from completing
+	assert.Equal(t, 3, len(results))
+
+	result2, _ := dispatcher.GetResult("task-2")
+	assert.Error(t, result2.Error)
+}
+
+func TestParallelExecution(t *testing.T) {
+	dispatcher := NewDispatcher(10)
+
+	// Create 9 tasks, each taking 100ms
+	tasks := make([]Task, 0)
+	for i := 1; i <= 9; i++ {
+		tasks = append(tasks, &MockTask{
+			id:        fmt.Sprintf("task-%d", i),
+			duration:  100 * time.Millisecond,
+			shouldErr: false,
+		})
+	}
+
+	start := time.Now()
+	results, err := dispatcher.DispatchAll(context.Background(), tasks)
+	elapsed := time.Since(start)
+
+	assert.NoError(t, err)
+	assert.Equal(t, 9, len(results))
+
+	// With parallel execution, should take ~100ms (not 900ms)
+	// Allow some margin (150ms)
+	assert.Less(t, elapsed, 150*time.Millisecond)
+}
+
+func TestSpeedup(t *testing.T) {
+	dispatcher := NewDispatcher(10)
+
+	tasks := make([]Task, 0)
+	for i := 1; i <= 9; i++ {
+		tasks = append(tasks, &MockTask{
+			id:        fmt.Sprintf("task-%d", i),
+			duration:  50 * time.Millisecond,
+			shouldErr: false,
+		})
+	}
+
+	_, _ = dispatcher.DispatchAll(context.Background(), tasks)
+
+	speedup := dispatcher.GetSpeedup()
+	// With 9 tasks running in parallel, speedup should be close to 9
+	assert.Greater(t, speedup, 8.0)
+	assert.Less(t, speedup, 10.0)
+}
+
+func TestExecutionTime(t *testing.T) {
+	dispatcher := NewDispatcher(10)
+
+	tasks := make([]Task, 0)
+	for i := 1; i <= 3; i++ {
+		tasks = append(tasks, &MockTask{
+			id:        fmt.Sprintf("task-%d", i),
+			duration:  100 * time.Millisecond,
+			shouldErr: false,
+		})
+	}
+
+	_, _ = dispatcher.DispatchAll(context.Background(), tasks)
+
+	executionTime := dispatcher.GetExecutionTime()
+	// Should be roughly 100ms (parallel execution)
+	assert.Greater(t, executionTime, 80*time.Millisecond)
+	assert.Less(t, executionTime, 200*time.Millisecond)
+}
+
+func TestTotalTaskDuration(t *testing.T) {
+	dispatcher := NewDispatcher(10)
+
+	tasks := make([]Task, 0)
+	for i := 1; i <= 3; i++ {
+		tasks = append(tasks, &MockTask{
+			id:        fmt.Sprintf("task-%d", i),
+			duration:  100 * time.Millisecond,
+			shouldErr: false,
+		})
+	}
+
+	_, _ = dispatcher.DispatchAll(context.Background(), tasks)
+
+	totalDuration := dispatcher.GetTotalTaskDuration()
+	// Sum should be roughly 300ms
+	assert.Greater(t, totalDuration, 290*time.Millisecond)
+	assert.Less(t, totalDuration, 350*time.Millisecond)
+}
+
+func TestGetStats(t *testing.T) {
+	dispatcher := NewDispatcher(5)
+
+	tasks := make([]Task, 0)
+	for i := 1; i <= 5; i++ {
+		tasks = append(tasks, &MockTask{
+			id:        fmt.Sprintf("task-%d", i),
+			duration:  50 * time.Millisecond,
+			shouldErr: false,
+		})
+	}
+
+	_, _ = dispatcher.DispatchAll(context.Background(), tasks)
+
+	stats := dispatcher.GetStats()
+	assert.Equal(t, 5, stats["total_tasks"])
+	assert.Equal(t, 5, stats["completed"])
+	assert.Equal(t, 5, stats["concurrency"])
+	assert.NotZero(t, stats["total_duration"])
+}
+
+func TestIsComplete(t *testing.T) {
+	dispatcher := NewDispatcher(1)
+
+	task := &MockTask{
+		id:        "task-1",
+		duration:  10 * time.Millisecond,
+		shouldErr: false,
+	}
+
+	dispatcher.DispatchAll(context.Background(), []Task{task})
+
+	assert.True(t, dispatcher.IsComplete("task-1"))
+	assert.False(t, dispatcher.IsComplete("task-2"))
+}
+
+func TestAreAllComplete(t *testing.T) {
+	dispatcher := NewDispatcher(5)
+
+	tasks := make([]Task, 0)
+	for i := 1; i <= 3; i++ {
+		tasks = append(tasks, &MockTask{
+			id:        fmt.Sprintf("task-%d", i),
+			duration:  10 * time.Millisecond,
+			shouldErr: false,
+		})
+	}
+
+	dispatcher.DispatchAll(context.Background(), tasks)
+
+	assert.True(t, dispatcher.AreAllComplete())
+}
+
+func TestGetCompletedCount(t *testing.T) {
+	dispatcher := NewDispatcher(5)
+
+	tasks := make([]Task, 0)
+	for i := 1; i <= 5; i++ {
+		tasks = append(tasks, &MockTask{
+			id:        fmt.Sprintf("task-%d", i),
+			duration:  10 * time.Millisecond,
+			shouldErr: false,
+		})
+	}
+
+	dispatcher.DispatchAll(context.Background(), tasks)
+
+	assert.Equal(t, 5, dispatcher.GetCompletedCount())
+}
+
+func TestConcurrencyLimit(t *testing.T) {
+	// Create dispatcher with low concurrency
+	dispatcher := NewDispatcher(2)
+
+	// All tasks should still complete
+	tasks := make([]Task, 0)
+	for i := 1; i <= 5; i++ {
+		tasks = append(tasks, &MockTask{
+			id:        fmt.Sprintf("task-%d", i),
+			duration:  10 * time.Millisecond,
+			shouldErr: false,
+		})
+	}
+
+	results, err := dispatcher.DispatchAll(context.Background(), tasks)
+	assert.NoError(t, err)
+	assert.Equal(t, 5, len(results))
+}
+
+func TestContextCancellation(t *testing.T) {
+	dispatcher := NewDispatcher(2) // Low concurrency
+
+	tasks := make([]Task, 0)
+	for i := 1; i <= 10; i++ {
+		tasks = append(tasks, &MockTask{
+			id:        fmt.Sprintf("task-%d", i),
+			duration:  500 * time.Millisecond,
+			shouldErr: false,
+		})
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	go func() {
+		time.Sleep(50 * time.Millisecond)
+		cancel()
+	}()
+
+	_, _ = dispatcher.DispatchAll(ctx, tasks)
+	// Some tasks may be cancelled
+	completed := dispatcher.GetCompletedCount()
+	assert.Less(t, completed, 10)
+}
+
+func TestEmptyTaskList(t *testing.T) {
+	dispatcher := NewDispatcher(5)
+
+	results, err := dispatcher.DispatchAll(context.Background(), []Task{})
+	assert.NoError(t, err)
+	assert.Equal(t, 0, len(results))
+}
+
+func TestTaskResultFields(t *testing.T) {
+	dispatcher := NewDispatcher(1)
+
+	task := &MockTask{
+		id:        "task-1",
+		duration:  50 * time.Millisecond,
+		shouldErr: false,
+	}
+
+	dispatcher.DispatchAll(context.Background(), []Task{task})
+
+	result, _ := dispatcher.GetResult("task-1")
+	assert.NotZero(t, result.StartTime)
+	assert.NotZero(t, result.EndTime)
+	assert.NotZero(t, result.Duration)
+	assert.True(t, result.EndTime.After(result.StartTime))
+}
+
+func BenchmarkParallelDispatch(b *testing.B) {
+	dispatcher := NewDispatcher(10)
+
+	for i := 0; i < b.N; i++ {
+		tasks := make([]Task, 0)
+		for j := 0; j < 10; j++ {
+			tasks = append(tasks, &MockTask{
+				id:        fmt.Sprintf("task-%d", j),
+				duration:  5 * time.Millisecond,
+				shouldErr: false,
+			})
+		}
+		dispatcher.DispatchAll(context.Background(), tasks)
+	}
+}
+
+func BenchmarkDispatchSingleTask(b *testing.B) {
+	dispatcher := NewDispatcher(1)
+
+	for i := 0; i < b.N; i++ {
+		task := &MockTask{
+			id:        "task-1",
+			duration:  5 * time.Millisecond,
+			shouldErr: false,
+		}
+		dispatcher.DispatchAll(context.Background(), []Task{task})
+	}
+}

internal/indexing/lessons_index.go

@@ -0,0 +1,390 @@
+package indexing
+
+import (
+	"bufio"
+	"encoding/json"
+	"fmt"
+	"os"
+	"strings"
+	"sync"
+	"time"
+)
+
+// Lesson represents a learned lesson from a past failure
+type Lesson struct {
+	ID            string                 `json:"id"`
+	TaskType      string                 `json:"task_type"`
+	ActivityType  string                 `json:"activity_type"`
+	FailureType   string                 `json:"failure_type"`
+	FailureMsg    string                 `json:"failure_msg"`
+	Resolution    string                 `json:"resolution"`
+	Pattern       string                 `json:"pattern"`
+	TimesSeen     int                    `json:"times_seen"`
+	LastSeen      time.Time              `json:"last_seen"`
+	FirstSeen     time.Time              `json:"first_seen"`
+	Metadata      map[string]interface{} `json:"metadata,omitempty"`
+}
+
+// LessonIndex provides fast indexed access to lessons
+type LessonIndex struct {
+	mu              sync.RWMutex
+	lessons         map[string]*Lesson           // ID -> Lesson
+	byTaskType      map[string][]*Lesson         // TaskType -> Lessons
+	byActivityType  map[string][]*Lesson         // ActivityType -> Lessons
+	byFailureType   map[string][]*Lesson         // FailureType -> Lessons
+	byPattern       map[string][]*Lesson         // Pattern -> Lessons
+	sourceFile      string
+	lastBuiltTime   time.Time
+	lessonCount     int
+	buildTime       time.Duration
+}
+
+// NewLessonIndex creates a new lesson index
+func NewLessonIndex() *LessonIndex {
+	return &LessonIndex{
+		lessons:        make(map[string]*Lesson),
+		byTaskType:     make(map[string][]*Lesson),
+		byActivityType: make(map[string][]*Lesson),
+		byFailureType:  make(map[string][]*Lesson),
+		byPattern:      make(map[string][]*Lesson),
+	}
+}
+
+// BuildFromFile loads lessons from a JSONL file and builds the index
+func (li *LessonIndex) BuildFromFile(filePath string) error {
+	li.mu.Lock()
+	defer li.mu.Unlock()
+
+	startTime := time.Now()
+
+	// Clear existing index
+	li.lessons = make(map[string]*Lesson)
+	li.byTaskType = make(map[string][]*Lesson)
+	li.byActivityType = make(map[string][]*Lesson)
+	li.byFailureType = make(map[string][]*Lesson)
+	li.byPattern = make(map[string][]*Lesson)
+
+	// Open file
+	file, err := os.Open(filePath)
+	if err != nil {
+		if os.IsNotExist(err) {
+			li.sourceFile = filePath
+			li.lastBuiltTime = time.Now()
+			li.buildTime = time.Since(startTime)
+			return nil // File doesn't exist yet
+		}
+		return err
+	}
+	defer file.Close()
+
+	// Read JSONL lines
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		var lesson Lesson
+		if err := json.Unmarshal(scanner.Bytes(), &lesson); err != nil {
+			continue // Skip malformed lines
+		}
+
+		li.addLessonLocked(&lesson)
+	}
+
+	if err := scanner.Err(); err != nil {
+		return err
+	}
+
+	li.sourceFile = filePath
+	li.lastBuiltTime = time.Now()
+	li.buildTime = time.Since(startTime)
+	li.lessonCount = len(li.lessons)
+
+	return nil
+}
+
+// addLessonLocked adds a lesson to all indexes (must be called with lock held)
+func (li *LessonIndex) addLessonLocked(lesson *Lesson) {
+	if lesson.ID == "" {
+		return
+	}
+
+	li.lessons[lesson.ID] = lesson
+
+	// Index by task type
+	if lesson.TaskType != "" {
+		li.byTaskType[lesson.TaskType] = append(li.byTaskType[lesson.TaskType], lesson)
+	}
+
+	// Index by activity type
+	if lesson.ActivityType != "" {
+		li.byActivityType[lesson.ActivityType] = append(li.byActivityType[lesson.ActivityType], lesson)
+	}
+
+	// Index by failure type
+	if lesson.FailureType != "" {
+		li.byFailureType[lesson.FailureType] = append(li.byFailureType[lesson.FailureType], lesson)
+	}
+
+	// Index by pattern
+	if lesson.Pattern != "" {
+		li.byPattern[lesson.Pattern] = append(li.byPattern[lesson.Pattern], lesson)
+	}
+}
+
+// AddLesson adds a single lesson and updates indexes
+func (li *LessonIndex) AddLesson(lesson *Lesson) {
+	li.mu.Lock()
+	defer li.mu.Unlock()
+
+	li.addLessonLocked(lesson)
+	li.lessonCount = len(li.lessons)
+}
+
+// FindByTaskType returns all lessons for a task type
+func (li *LessonIndex) FindByTaskType(taskType string) []*Lesson {
+	li.mu.RLock()
+	defer li.mu.RUnlock()
+
+	if lessons, exists := li.byTaskType[taskType]; exists {
+		// Return a copy to prevent external modifications
+		result := make([]*Lesson, len(lessons))
+		copy(result, lessons)
+		return result
+	}
+
+	return make([]*Lesson, 0)
+}
+
+// FindByActivityType returns all lessons for an activity type
+func (li *LessonIndex) FindByActivityType(activityType string) []*Lesson {
+	li.mu.RLock()
+	defer li.mu.RUnlock()
+
+	if lessons, exists := li.byActivityType[activityType]; exists {
+		result := make([]*Lesson, len(lessons))
+		copy(result, lessons)
+		return result
+	}
+
+	return make([]*Lesson, 0)
+}
+
+// FindByFailureType returns all lessons for a failure type
+func (li *LessonIndex) FindByFailureType(failureType string) []*Lesson {
+	li.mu.RLock()
+	defer li.mu.RUnlock()
+
+	if lessons, exists := li.byFailureType[failureType]; exists {
+		result := make([]*Lesson, len(lessons))
+		copy(result, lessons)
+		return result
+	}
+
+	return make([]*Lesson, 0)
+}
+
+// FindByPattern returns all lessons matching a pattern
+func (li *LessonIndex) FindByPattern(pattern string) []*Lesson {
+	li.mu.RLock()
+	defer li.mu.RUnlock()
+
+	if lessons, exists := li.byPattern[pattern]; exists {
+		result := make([]*Lesson, len(lessons))
+		copy(result, lessons)
+		return result
+	}
+
+	return make([]*Lesson, 0)
+}
+
+// FindSimilar returns lessons containing a substring in failure message
+func (li *LessonIndex) FindSimilar(substr string) []*Lesson {
+	li.mu.RLock()
+	defer li.mu.RUnlock()
+
+	var results []*Lesson
+	substr = strings.ToLower(substr)
+
+	for _, lesson := range li.lessons {
+		if strings.Contains(strings.ToLower(lesson.FailureMsg), substr) {
+			results = append(results, lesson)
+		}
+	}
+
+	return results
+}
+
+// GetLesson returns a specific lesson by ID
+func (li *LessonIndex) GetLesson(id string) (*Lesson, bool) {
+	li.mu.RLock()
+	defer li.mu.RUnlock()
+
+	lesson, exists := li.lessons[id]
+	return lesson, exists
+}
+
+// GetStats returns index statistics
+func (li *LessonIndex) GetStats() map[string]interface{} {
+	li.mu.RLock()
+	defer li.mu.RUnlock()
+
+	return map[string]interface{}{
+		"total_lessons":       len(li.lessons),
+		"unique_task_types":   len(li.byTaskType),
+		"unique_activity_types": len(li.byActivityType),
+		"unique_failure_types": len(li.byFailureType),
+		"unique_patterns":     len(li.byPattern),
+		"last_built_time":     li.lastBuiltTime,
+		"build_time":          li.buildTime,
+		"source_file":         li.sourceFile,
+	}
+}
+
+// GetAllLessons returns all lessons (for export/debugging)
+func (li *LessonIndex) GetAllLessons() []*Lesson {
+	li.mu.RLock()
+	defer li.mu.RUnlock()
+
+	result := make([]*Lesson, 0, len(li.lessons))
+	for _, lesson := range li.lessons {
+		result = append(result, lesson)
+	}
+
+	return result
+}
+
+// Count returns the total number of indexed lessons
+func (li *LessonIndex) Count() int {
+	li.mu.RLock()
+	defer li.mu.RUnlock()
+
+	return len(li.lessons)
+}
+
+// Clear clears all indexes
+func (li *LessonIndex) Clear() {
+	li.mu.Lock()
+	defer li.mu.Unlock()
+
+	li.lessons = make(map[string]*Lesson)
+	li.byTaskType = make(map[string][]*Lesson)
+	li.byActivityType = make(map[string][]*Lesson)
+	li.byFailureType = make(map[string][]*Lesson)
+	li.byPattern = make(map[string][]*Lesson)
+	li.lessonCount = 0
+}
+
+// Rebuild rebuilds the index from the source file
+func (li *LessonIndex) Rebuild() error {
+	if li.sourceFile == "" {
+		return fmt.Errorf("no source file set")
+	}
+
+	return li.BuildFromFile(li.sourceFile)
+}
+
+// QueryMultiple performs a multi-field query (AND logic)
+func (li *LessonIndex) QueryMultiple(taskType, activityType, failureType string) []*Lesson {
+	li.mu.RLock()
+	defer li.mu.RUnlock()
+
+	// Start with the most restrictive set
+	var candidates []*Lesson
+
+	// Choose the smallest set to iterate from
+	if taskType != "" && activityType != "" && failureType != "" {
+		// Use the smallest set
+		sizes := []int{
+			len(li.byTaskType[taskType]),
+			len(li.byActivityType[activityType]),
+			len(li.byFailureType[failureType]),
+		}
+
+		minIdx := 0
+		for i, size := range sizes {
+			if size < sizes[minIdx] {
+				minIdx = i
+			}
+		}
+
+		if minIdx == 0 {
+			candidates = li.byTaskType[taskType]
+		} else if minIdx == 1 {
+			candidates = li.byActivityType[activityType]
+		} else {
+			candidates = li.byFailureType[failureType]
+		}
+	} else if taskType != "" && activityType != "" {
+		if len(li.byTaskType[taskType]) <= len(li.byActivityType[activityType]) {
+			candidates = li.byTaskType[taskType]
+		} else {
+			candidates = li.byActivityType[activityType]
+		}
+	} else if taskType != "" {
+		candidates = li.byTaskType[taskType]
+	} else if activityType != "" {
+		candidates = li.byActivityType[activityType]
+	} else if failureType != "" {
+		candidates = li.byFailureType[failureType]
+	}
+
+	// Filter candidates
+	var results []*Lesson
+	for _, lesson := range candidates {
+		if taskType != "" && lesson.TaskType != taskType {
+			continue
+		}
+		if activityType != "" && lesson.ActivityType != activityType {
+			continue
+		}
+		if failureType != "" && lesson.FailureType != failureType {
+			continue
+		}
+
+		results = append(results, lesson)
+	}
+
+	return results
+}
+
+// GetByTimeRange returns lessons seen within a time range
+func (li *LessonIndex) GetByTimeRange(startTime, endTime time.Time) []*Lesson {
+	li.mu.RLock()
+	defer li.mu.RUnlock()
+
+	var results []*Lesson
+	for _, lesson := range li.lessons {
+		if !lesson.LastSeen.IsZero() &&
+			lesson.LastSeen.After(startTime) &&
+			lesson.LastSeen.Before(endTime) {
+			results = append(results, lesson)
+		}
+	}
+
+	return results
+}
+
+// GetMostFrequentFailures returns the most frequently seen failures
+func (li *LessonIndex) GetMostFrequentFailures(limit int) []*Lesson {
+	li.mu.RLock()
+	defer li.mu.RUnlock()
+
+	// Convert to slice
+	var lessons []*Lesson
+	for _, lesson := range li.lessons {
+		lessons = append(lessons, lesson)
+	}
+
+	// Simple bubble sort (in practice, use a proper sort)
+	for i := 0; i < len(lessons); i++ {
+		for j := i + 1; j < len(lessons); j++ {
+			if lessons[j].TimesSeen > lessons[i].TimesSeen {
+				lessons[i], lessons[j] = lessons[j], lessons[i]
+			}
+		}
+	}
+
+	if limit > len(lessons) {
+		limit = len(lessons)
+	}
+
+	return lessons[:limit]
+}

internal/indexing/lessons_index_test.go

@@ -0,0 +1,467 @@
+package indexing
+
+import (
+	"encoding/json"
+	"os"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func createTestLessonsFile(t *testing.T, count int) string {
+	file, err := os.CreateTemp("", "lessons-*.jsonl")
+	assert.NoError(t, err)
+	defer file.Close()
+
+	for i := 0; i < count; i++ {
+		lesson := Lesson{
+			ID:           "lesson-" + string(rune(48+i%10)) + "-" + string(rune(48+i/10)),
+			TaskType:     []string{"add_feature", "fix_bug", "refactor"}[i%3],
+			ActivityType: []string{"implementer", "judge", "planner"}[i%3],
+			FailureType:  []string{"syntax_error", "logic_error", "timeout"}[i%3],
+			FailureMsg:   "Error message " + string(rune(48+i%100)),
+			Resolution:   "Fix strategy",
+			Pattern:      "pattern-" + string(rune(48+i%5)),
+			TimesSeen:    i % 10,
+			LastSeen:     time.Now().Add(-time.Duration(i) * time.Hour),
+			FirstSeen:    time.Now().Add(-time.Duration(i*24) * time.Hour),
+			Metadata: map[string]interface{}{
+				"index": i,
+			},
+		}
+
+		data, _ := json.Marshal(lesson)
+		file.WriteString(string(data) + "\n")
+	}
+
+	return file.Name()
+}
+
+
+
+func TestNewLessonIndex(t *testing.T) {
+	index := NewLessonIndex()
+	assert.NotNil(t, index)
+	assert.Equal(t, 0, index.Count())
+}
+
+func TestBuildFromFile(t *testing.T) {
+	file := createTestLessonsFile(t, 50)
+	defer os.Remove(file)
+
+	index := NewLessonIndex()
+	err := index.BuildFromFile(file)
+	assert.NoError(t, err)
+	assert.Greater(t, index.Count(), 0)
+}
+
+func TestAddLesson(t *testing.T) {
+	index := NewLessonIndex()
+
+	lesson := &Lesson{
+		ID:           "test-1",
+		TaskType:     "add_feature",
+		ActivityType: "implementer",
+		FailureType:  "syntax_error",
+		FailureMsg:   "Missing semicolon",
+		Resolution:   "Add semicolon",
+		Pattern:      "syntax-missing-semi",
+		TimesSeen:    1,
+		LastSeen:     time.Now(),
+		FirstSeen:    time.Now(),
+	}
+
+	index.AddLesson(lesson)
+	assert.Equal(t, 1, index.Count())
+
+	retrieved, exists := index.GetLesson("test-1")
+	assert.True(t, exists)
+	assert.Equal(t, "test-1", retrieved.ID)
+}
+
+func TestFindByTaskType(t *testing.T) {
+	index := NewLessonIndex()
+
+	lessons := []*Lesson{
+		{ID: "1", TaskType: "add_feature", ActivityType: "implementer"},
+		{ID: "2", TaskType: "add_feature", ActivityType: "judge"},
+		{ID: "3", TaskType: "fix_bug", ActivityType: "implementer"},
+	}
+
+	for _, lesson := range lessons {
+		index.AddLesson(lesson)
+	}
+
+	results := index.FindByTaskType("add_feature")
+	assert.Equal(t, 2, len(results))
+}
+
+func TestFindByActivityType(t *testing.T) {
+	index := NewLessonIndex()
+
+	lessons := []*Lesson{
+		{ID: "1", TaskType: "add_feature", ActivityType: "implementer"},
+		{ID: "2", TaskType: "add_feature", ActivityType: "implementer"},
+		{ID: "3", TaskType: "fix_bug", ActivityType: "judge"},
+	}
+
+	for _, lesson := range lessons {
+		index.AddLesson(lesson)
+	}
+
+	results := index.FindByActivityType("implementer")
+	assert.Equal(t, 2, len(results))
+}
+
+func TestFindByFailureType(t *testing.T) {
+	index := NewLessonIndex()
+
+	lessons := []*Lesson{
+		{ID: "1", FailureType: "syntax_error"},
+		{ID: "2", FailureType: "syntax_error"},
+		{ID: "3", FailureType: "logic_error"},
+	}
+
+	for _, lesson := range lessons {
+		index.AddLesson(lesson)
+	}
+
+	results := index.FindByFailureType("syntax_error")
+	assert.Equal(t, 2, len(results))
+}
+
+func TestFindByPattern(t *testing.T) {
+	index := NewLessonIndex()
+
+	lessons := []*Lesson{
+		{ID: "1", Pattern: "pattern-1"},
+		{ID: "2", Pattern: "pattern-2"},
+		{ID: "3", Pattern: "pattern-1"},
+	}
+
+	for _, lesson := range lessons {
+		index.AddLesson(lesson)
+	}
+
+	results := index.FindByPattern("pattern-1")
+	assert.Equal(t, 2, len(results))
+}
+
+func TestFindSimilar(t *testing.T) {
+	index := NewLessonIndex()
+
+	lessons := []*Lesson{
+		{ID: "1", FailureMsg: "Syntax error: missing semicolon"},
+		{ID: "2", FailureMsg: "Logic error: wrong condition"},
+		{ID: "3", FailureMsg: "Syntax error: missing bracket"},
+	}
+
+	for _, lesson := range lessons {
+		index.AddLesson(lesson)
+	}
+
+	results := index.FindSimilar("syntax")
+	assert.Equal(t, 2, len(results))
+}
+
+func TestQueryMultiple(t *testing.T) {
+	index := NewLessonIndex()
+
+	lessons := []*Lesson{
+		{ID: "1", TaskType: "add_feature", ActivityType: "implementer", FailureType: "syntax_error"},
+		{ID: "2", TaskType: "add_feature", ActivityType: "judge", FailureType: "syntax_error"},
+		{ID: "3", TaskType: "fix_bug", ActivityType: "implementer", FailureType: "logic_error"},
+	}
+
+	for _, lesson := range lessons {
+		index.AddLesson(lesson)
+	}
+
+	results := index.QueryMultiple("add_feature", "implementer", "syntax_error")
+	assert.Equal(t, 1, len(results))
+	assert.Equal(t, "1", results[0].ID)
+}
+
+func TestGetByTimeRange(t *testing.T) {
+	index := NewLessonIndex()
+
+	now := time.Now()
+	lessons := []*Lesson{
+		{ID: "1", LastSeen: now.Add(-2 * time.Hour)},
+		{ID: "2", LastSeen: now.Add(-1 * time.Hour)},
+		{ID: "3", LastSeen: now.Add(-24 * time.Hour)},
+	}
+
+	for _, lesson := range lessons {
+		index.AddLesson(lesson)
+	}
+
+	// Range before any lessons should find 0
+	results := index.GetByTimeRange(now.Add(-48*time.Hour), now.Add(-25*time.Hour))
+	assert.Equal(t, 0, len(results))
+
+	// Range that includes all lessons
+	results = index.GetByTimeRange(now.Add(-25*time.Hour), now)
+	assert.Equal(t, 3, len(results))
+
+	// Range that includes only recent lessons (1 and 2)
+	results = index.GetByTimeRange(now.Add(-3*time.Hour), now)
+	assert.Equal(t, 2, len(results))
+}
+
+func TestGetStats(t *testing.T) {
+	index := NewLessonIndex()
+
+	lessons := []*Lesson{
+		{ID: "1", TaskType: "add_feature", ActivityType: "implementer"},
+		{ID: "2", TaskType: "add_feature", ActivityType: "judge"},
+		{ID: "3", TaskType: "fix_bug", ActivityType: "implementer"},
+	}
+
+	for _, lesson := range lessons {
+		index.AddLesson(lesson)
+	}
+
+	stats := index.GetStats()
+	assert.Equal(t, 3, stats["total_lessons"])
+	assert.Equal(t, 2, stats["unique_task_types"])
+	assert.Equal(t, 2, stats["unique_activity_types"])
+}
+
+func TestGetAllLessons(t *testing.T) {
+	index := NewLessonIndex()
+
+	lessons := []*Lesson{
+		{ID: "1"},
+		{ID: "2"},
+		{ID: "3"},
+	}
+
+	for _, lesson := range lessons {
+		index.AddLesson(lesson)
+	}
+
+	all := index.GetAllLessons()
+	assert.Equal(t, 3, len(all))
+}
+
+func TestClear(t *testing.T) {
+	index := NewLessonIndex()
+
+	index.AddLesson(&Lesson{ID: "1"})
+	index.AddLesson(&Lesson{ID: "2"})
+	assert.Equal(t, 2, index.Count())
+
+	index.Clear()
+	assert.Equal(t, 0, index.Count())
+}
+
+func TestGetMostFrequentFailures(t *testing.T) {
+	index := NewLessonIndex()
+
+	lessons := []*Lesson{
+		{ID: "1", TimesSeen: 5},
+		{ID: "2", TimesSeen: 10},
+		{ID: "3", TimesSeen: 3},
+	}
+
+	for _, lesson := range lessons {
+		index.AddLesson(lesson)
+	}
+
+	top := index.GetMostFrequentFailures(2)
+	assert.Equal(t, 2, len(top))
+	assert.Equal(t, 10, top[0].TimesSeen)
+	assert.Equal(t, 5, top[1].TimesSeen)
+}
+
+func TestLookupLatency(t *testing.T) {
+	index := NewLessonIndex()
+
+	// Add 1000 lessons
+	for i := 0; i < 1000; i++ {
+		lesson := &Lesson{
+			ID:           "lesson-" + string(rune(48+i%100)),
+			TaskType:     "add_feature",
+			ActivityType: "implementer",
+			FailureType:  "syntax_error",
+		}
+		index.AddLesson(lesson)
+	}
+
+	// Measure lookup time
+	start := time.Now()
+	results := index.FindByTaskType("add_feature")
+	elapsed := time.Since(start)
+
+	assert.Greater(t, len(results), 0)
+	// Should be < 10ms
+	assert.Less(t, elapsed, 10*time.Millisecond)
+}
+
+func TestLookupLatencyLarge(t *testing.T) {
+	index := NewLessonIndex()
+
+	// Add 10000 lessons
+	for i := 0; i < 10000; i++ {
+		lesson := &Lesson{
+			ID:           "lesson-" + string(rune(48+i%100)),
+			TaskType:     []string{"add_feature", "fix_bug", "refactor"}[i%3],
+			ActivityType: []string{"implementer", "judge", "planner"}[i%3],
+			FailureType:  "syntax_error",
+		}
+		index.AddLesson(lesson)
+	}
+
+	// Measure lookup time
+	start := time.Now()
+	results := index.FindByActivityType("implementer")
+	elapsed := time.Since(start)
+
+	assert.Greater(t, len(results), 0)
+	// Should be < 10ms even with 10k entries
+	assert.Less(t, elapsed, 10*time.Millisecond)
+}
+
+func TestConcurrentQueries(t *testing.T) {
+	index := NewLessonIndex()
+
+	// Add lessons
+	for i := 0; i < 100; i++ {
+		lesson := &Lesson{
+			ID:           "lesson-" + string(rune(48+i%10)),
+			TaskType:     "add_feature",
+			ActivityType: "implementer",
+			FailureType:  "syntax_error",
+		}
+		index.AddLesson(lesson)
+	}
+
+	// Run concurrent queries
+	done := make(chan bool, 10)
+	for i := 0; i < 10; i++ {
+		go func() {
+			results := index.FindByTaskType("add_feature")
+			assert.Greater(t, len(results), 0)
+			done <- true
+		}()
+	}
+
+	for i := 0; i < 10; i++ {
+		<-done
+	}
+}
+
+func TestEmptyQueries(t *testing.T) {
+	index := NewLessonIndex()
+
+	results := index.FindByTaskType("nonexistent")
+	assert.Equal(t, 0, len(results))
+
+	results = index.FindByActivityType("nonexistent")
+	assert.Equal(t, 0, len(results))
+
+	results = index.FindByFailureType("nonexistent")
+	assert.Equal(t, 0, len(results))
+}
+
+func TestGetLesson(t *testing.T) {
+	index := NewLessonIndex()
+
+	lesson := &Lesson{ID: "test-1", TaskType: "add_feature"}
+	index.AddLesson(lesson)
+
+	retrieved, exists := index.GetLesson("test-1")
+	assert.True(t, exists)
+	assert.Equal(t, "test-1", retrieved.ID)
+
+	_, exists = index.GetLesson("nonexistent")
+	assert.False(t, exists)
+}
+
+func TestMultipleIndexes(t *testing.T) {
+	index := NewLessonIndex()
+
+	lesson := &Lesson{
+		ID:           "1",
+		TaskType:     "add_feature",
+		ActivityType: "implementer",
+		FailureType:  "syntax_error",
+		Pattern:      "pattern-1",
+	}
+
+	index.AddLesson(lesson)
+
+	// Should be findable by all indexes
+	assert.Equal(t, 1, len(index.FindByTaskType("add_feature")))
+	assert.Equal(t, 1, len(index.FindByActivityType("implementer")))
+	assert.Equal(t, 1, len(index.FindByFailureType("syntax_error")))
+	assert.Equal(t, 1, len(index.FindByPattern("pattern-1")))
+}
+
+func TestRebuild(t *testing.T) {
+	file := createTestLessonsFile(t, 50)
+	defer os.Remove(file)
+
+	index := NewLessonIndex()
+	_ = index.BuildFromFile(file)
+	count1 := index.Count()
+
+	_ = index.Rebuild()
+	count2 := index.Count()
+
+	assert.Equal(t, count1, count2)
+}
+
+func BenchmarkAddLesson(b *testing.B) {
+	index := NewLessonIndex()
+
+	for i := 0; i < b.N; i++ {
+		lesson := &Lesson{
+			ID:           "lesson-" + string(rune(48+i%100)),
+			TaskType:     "add_feature",
+			ActivityType: "implementer",
+			FailureType:  "syntax_error",
+		}
+		index.AddLesson(lesson)
+	}
+}
+
+func BenchmarkFindByTaskType(b *testing.B) {
+	index := NewLessonIndex()
+
+	// Populate index
+	for i := 0; i < 1000; i++ {
+		lesson := &Lesson{
+			ID:           "lesson-" + string(rune(48+i%100)),
+			TaskType:     "add_feature",
+			ActivityType: "implementer",
+		}
+		index.AddLesson(lesson)
+	}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		index.FindByTaskType("add_feature")
+	}
+}
+
+func BenchmarkFindByActivityType(b *testing.B) {
+	index := NewLessonIndex()
+
+	// Populate index
+	for i := 0; i < 1000; i++ {
+		lesson := &Lesson{
+			ID:           "lesson-" + string(rune(48+i%100)),
+			TaskType:     "add_feature",
+			ActivityType: "implementer",
+		}
+		index.AddLesson(lesson)
+	}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		index.FindByActivityType("implementer")
+	}
+}

internal/templates/engine.go

@@ -0,0 +1,236 @@
+package templates
+
+import (
+	"bytes"
+	"fmt"
+	"sync"
+	"text/template"
+	"time"
+)
+
+// TemplateEngine pre-compiles and caches Go templates for fast rendering
+type TemplateEngine struct {
+	mu        sync.RWMutex
+	cache     map[string]*CachedTemplate
+	maxSize   int
+	compileStats map[string]*CompileStats
+}
+
+// CachedTemplate holds a compiled template with metrics
+type CachedTemplate struct {
+	Template  *template.Template
+	CompiledAt time.Time
+	RenderCount int
+	RenderTime time.Duration
+}
+
+// CompileStats tracks compilation statistics
+type CompileStats struct {
+	TemplateName string
+	CompileTime  time.Duration
+	CompiledAt   time.Time
+	RenderCount  int
+	TotalRenderTime time.Duration
+	AvgRenderTime time.Duration
+}
+
+// NewTemplateEngine creates a new template engine
+func NewTemplateEngine(maxSize int) *TemplateEngine {
+	if maxSize <= 0 {
+		maxSize = 100
+	}
+
+	return &TemplateEngine{
+		cache:        make(map[string]*CachedTemplate),
+		maxSize:      maxSize,
+		compileStats: make(map[string]*CompileStats),
+	}
+}
+
+// Compile compiles and caches a template
+func (te *TemplateEngine) Compile(name string, templateStr string) (*template.Template, error) {
+	te.mu.Lock()
+	defer te.mu.Unlock()
+
+	// Check if already cached
+	if cached, exists := te.cache[name]; exists {
+		return cached.Template, nil
+	}
+
+	// Compile the template
+	startTime := time.Now()
+	tmpl, err := template.New(name).Parse(templateStr)
+	compileTime := time.Since(startTime)
+
+	if err != nil {
+		return nil, err
+	}
+
+	// Check size limit
+	if len(te.cache) >= te.maxSize {
+		// Simple FIFO eviction
+		var oldestName string
+		var oldestTime time.Time
+
+		for n, t := range te.cache {
+			if oldestTime.IsZero() || t.CompiledAt.Before(oldestTime) {
+				oldestName = n
+				oldestTime = t.CompiledAt
+			}
+		}
+
+		if oldestName != "" {
+			delete(te.cache, oldestName)
+			delete(te.compileStats, oldestName)
+		}
+	}
+
+	// Cache the compiled template
+	cached := &CachedTemplate{
+		Template:   tmpl,
+		CompiledAt: time.Now(),
+	}
+
+	te.cache[name] = cached
+
+	// Track compilation stats
+	te.compileStats[name] = &CompileStats{
+		TemplateName: name,
+		CompileTime:  compileTime,
+		CompiledAt:   time.Now(),
+	}
+
+	return tmpl, nil
+}
+
+// Render renders a cached template with the given data
+func (te *TemplateEngine) Render(name string, data interface{}) (string, error) {
+	te.mu.RLock()
+	cached, exists := te.cache[name]
+	te.mu.RUnlock()
+
+	if !exists {
+		return "", fmt.Errorf("template not found: %s", name)
+	}
+
+	// Render template
+	startTime := time.Now()
+	var buf bytes.Buffer
+	err := cached.Template.Execute(&buf, data)
+	renderTime := time.Since(startTime)
+
+	if err != nil {
+		return "", err
+	}
+
+	// Update stats
+	te.mu.Lock()
+	cached.RenderCount++
+	cached.RenderTime += renderTime
+
+	if stats, exists := te.compileStats[name]; exists {
+		stats.RenderCount++
+		stats.TotalRenderTime += renderTime
+		if stats.RenderCount > 0 {
+			stats.AvgRenderTime = stats.TotalRenderTime / time.Duration(stats.RenderCount)
+		}
+	}
+	te.mu.Unlock()
+
+	return buf.String(), nil
+}
+
+// CompileAndRender compiles (if not cached) and renders a template
+func (te *TemplateEngine) CompileAndRender(name string, templateStr string, data interface{}) (string, error) {
+	_, err := te.Compile(name, templateStr)
+	if err != nil {
+		return "", err
+	}
+
+	return te.Render(name, data)
+}
+
+// GetStats returns compilation statistics
+func (te *TemplateEngine) GetStats(name string) (*CompileStats, bool) {
+	te.mu.RLock()
+	defer te.mu.RUnlock()
+
+	stats, exists := te.compileStats[name]
+	return stats, exists
+}
+
+// GetAllStats returns all compilation statistics
+func (te *TemplateEngine) GetAllStats() map[string]*CompileStats {
+	te.mu.RLock()
+	defer te.mu.RUnlock()
+
+	statsCopy := make(map[string]*CompileStats)
+	for name, stats := range te.compileStats {
+		statsCopy[name] = stats
+	}
+
+	return statsCopy
+}
+
+// Clear clears all cached templates
+func (te *TemplateEngine) Clear() {
+	te.mu.Lock()
+	defer te.mu.Unlock()
+
+	te.cache = make(map[string]*CachedTemplate)
+	te.compileStats = make(map[string]*CompileStats)
+}
+
+// CacheSize returns the current cache size
+func (te *TemplateEngine) CacheSize() int {
+	te.mu.RLock()
+	defer te.mu.RUnlock()
+
+	return len(te.cache)
+}
+
+// IsCached checks if a template is cached
+func (te *TemplateEngine) IsCached(name string) bool {
+	te.mu.RLock()
+	defer te.mu.RUnlock()
+
+	_, exists := te.cache[name]
+	return exists
+}
+
+// Remove removes a template from cache
+func (te *TemplateEngine) Remove(name string) {
+	te.mu.Lock()
+	defer te.mu.Unlock()
+
+	delete(te.cache, name)
+	delete(te.compileStats, name)
+}
+
+// GetCacheStats returns overall cache statistics
+func (te *TemplateEngine) GetCacheStats() map[string]interface{} {
+	te.mu.RLock()
+	defer te.mu.RUnlock()
+
+	totalRenders := 0
+	totalRenderTime := time.Duration(0)
+
+	for _, stats := range te.compileStats {
+		totalRenders += stats.RenderCount
+		totalRenderTime += stats.TotalRenderTime
+	}
+
+	avgRenderTime := time.Duration(0)
+	if totalRenders > 0 {
+		avgRenderTime = totalRenderTime / time.Duration(totalRenders)
+	}
+
+	return map[string]interface{}{
+		"cache_size":           len(te.cache),
+		"max_size":             te.maxSize,
+		"total_renders":        totalRenders,
+		"total_render_time":    totalRenderTime,
+		"avg_render_time":      avgRenderTime,
+		"usage_ratio":          float64(len(te.cache)) / float64(te.maxSize),
+	}
+}

internal/templates/engine_test.go

@@ -0,0 +1,238 @@
+package templates
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestNewTemplateEngine(t *testing.T) {
+	engine := NewTemplateEngine(50)
+	assert.NotNil(t, engine)
+	assert.Equal(t, 50, engine.maxSize)
+	assert.Equal(t, 0, engine.CacheSize())
+}
+
+func TestCompile(t *testing.T) {
+	engine := NewTemplateEngine(50)
+
+	tmpl, err := engine.Compile("test", "Hello {{.Name}}!")
+	assert.NoError(t, err)
+	assert.NotNil(t, tmpl)
+	assert.True(t, engine.IsCached("test"))
+}
+
+func TestCompileDuplicate(t *testing.T) {
+	engine := NewTemplateEngine(50)
+
+	tmpl1, _ := engine.Compile("test", "Hello {{.Name}}!")
+	tmpl2, _ := engine.Compile("test", "Hello {{.Name}}!")
+
+	// Should return the same cached template
+	assert.Equal(t, tmpl1, tmpl2)
+	assert.Equal(t, 1, engine.CacheSize())
+}
+
+func TestRender(t *testing.T) {
+	engine := NewTemplateEngine(50)
+
+	engine.Compile("test", "Hello {{.Name}}!")
+	result, err := engine.Render("test", map[string]string{"Name": "World"})
+
+	assert.NoError(t, err)
+	assert.Equal(t, "Hello World!", result)
+}
+
+func TestRenderNotFound(t *testing.T) {
+	engine := NewTemplateEngine(50)
+
+	_, err := engine.Render("nonexistent", map[string]string{})
+	assert.Error(t, err)
+}
+
+func TestCompileAndRender(t *testing.T) {
+	engine := NewTemplateEngine(50)
+
+	result, err := engine.CompileAndRender("test", "{{.X}} + {{.Y}} = {{.Z}}", map[string]int{
+		"X": 2,
+		"Y": 3,
+		"Z": 5,
+	})
+
+	assert.NoError(t, err)
+	assert.Equal(t, "2 + 3 = 5", result)
+}
+
+func TestRenderMultipleTimes(t *testing.T) {
+	engine := NewTemplateEngine(50)
+
+	engine.Compile("test", "Count: {{.}}")
+
+	result1, _ := engine.Render("test", 1)
+	result2, _ := engine.Render("test", 2)
+	result3, _ := engine.Render("test", 3)
+
+	assert.Equal(t, "Count: 1", result1)
+	assert.Equal(t, "Count: 2", result2)
+	assert.Equal(t, "Count: 3", result3)
+
+	stats, _ := engine.GetStats("test")
+	assert.Equal(t, 3, stats.RenderCount)
+}
+
+func TestGetStats(t *testing.T) {
+	engine := NewTemplateEngine(50)
+
+	engine.Compile("test", "Hello")
+	stats, exists := engine.GetStats("test")
+
+	assert.True(t, exists)
+	assert.NotNil(t, stats)
+	assert.Equal(t, "test", stats.TemplateName)
+	assert.NotZero(t, stats.CompileTime)
+}
+
+func TestGetAllStats(t *testing.T) {
+	engine := NewTemplateEngine(50)
+
+	engine.Compile("test1", "Template 1")
+	engine.Compile("test2", "Template 2")
+	engine.Compile("test3", "Template 3")
+
+	allStats := engine.GetAllStats()
+	assert.Equal(t, 3, len(allStats))
+	assert.NotNil(t, allStats["test1"])
+	assert.NotNil(t, allStats["test2"])
+	assert.NotNil(t, allStats["test3"])
+}
+
+func TestClear(t *testing.T) {
+	engine := NewTemplateEngine(50)
+
+	engine.Compile("test1", "Template 1")
+	engine.Compile("test2", "Template 2")
+	assert.Equal(t, 2, engine.CacheSize())
+
+	engine.Clear()
+	assert.Equal(t, 0, engine.CacheSize())
+	assert.False(t, engine.IsCached("test1"))
+}
+
+func TestRemove(t *testing.T) {
+	engine := NewTemplateEngine(50)
+
+	engine.Compile("test1", "Template 1")
+	engine.Compile("test2", "Template 2")
+	assert.Equal(t, 2, engine.CacheSize())
+
+	engine.Remove("test1")
+	assert.Equal(t, 1, engine.CacheSize())
+	assert.False(t, engine.IsCached("test1"))
+	assert.True(t, engine.IsCached("test2"))
+}
+
+func TestCacheEviction(t *testing.T) {
+	engine := NewTemplateEngine(3)
+
+	engine.Compile("test1", "Template 1")
+	engine.Compile("test2", "Template 2")
+	engine.Compile("test3", "Template 3")
+	assert.Equal(t, 3, engine.CacheSize())
+
+	// Adding a 4th template should evict the oldest (test1)
+	time.Sleep(10 * time.Millisecond)
+	engine.Compile("test4", "Template 4")
+
+	assert.Equal(t, 3, engine.CacheSize())
+	assert.False(t, engine.IsCached("test1"))
+	assert.True(t, engine.IsCached("test2"))
+	assert.True(t, engine.IsCached("test3"))
+	assert.True(t, engine.IsCached("test4"))
+}
+
+func TestIsCached(t *testing.T) {
+	engine := NewTemplateEngine(50)
+
+	assert.False(t, engine.IsCached("test"))
+
+	engine.Compile("test", "Template")
+
+	assert.True(t, engine.IsCached("test"))
+}
+
+func TestGetCacheStats(t *testing.T) {
+	engine := NewTemplateEngine(50)
+
+	engine.Compile("test1", "Template 1")
+	engine.Render("test1", "data")
+
+	engine.Compile("test2", "Template 2")
+	engine.Render("test2", "data")
+	engine.Render("test2", "data")
+
+	stats := engine.GetCacheStats()
+	assert.Equal(t, 2, stats["cache_size"])
+	assert.Equal(t, 50, stats["max_size"])
+	assert.Equal(t, 3, stats["total_renders"])
+	assert.NotZero(t, stats["total_render_time"])
+}
+
+func TestComplexTemplate(t *testing.T) {
+	engine := NewTemplateEngine(50)
+
+	templateStr := `
+	{{range .Items}}
+	- {{.Name}}: {{.Value}}
+	{{end}}
+	`
+
+	data := map[string]interface{}{
+		"Items": []map[string]interface{}{
+			{"Name": "Item1", "Value": 10},
+			{"Name": "Item2", "Value": 20},
+		},
+	}
+
+	result, err := engine.CompileAndRender("list", templateStr, data)
+	assert.NoError(t, err)
+	assert.Contains(t, result, "Item1")
+	assert.Contains(t, result, "Item2")
+}
+
+func TestRenderLatency(t *testing.T) {
+	engine := NewTemplateEngine(50)
+
+	engine.Compile("test", "Hello {{.Name}}!")
+
+	start := time.Now()
+	_, _ = engine.Render("test", map[string]string{"Name": "World"})
+	latency := time.Since(start)
+
+	// Should be < 100ms even accounting for slow systems
+	assert.Less(t, latency, 100*time.Millisecond)
+}
+
+func TestParseError(t *testing.T) {
+	engine := NewTemplateEngine(50)
+
+	_, err := engine.Compile("test", "{{.Name} missing closing bracket")
+	assert.Error(t, err)
+}
+
+func BenchmarkRender(b *testing.B) {
+	engine := NewTemplateEngine(50)
+	engine.Compile("test", "Hello {{.Name}}!")
+
+	for i := 0; i < b.N; i++ {
+		engine.Render("test", map[string]string{"Name": "World"})
+	}
+}
+
+func BenchmarkCompileAndRender(b *testing.B) {
+	engine := NewTemplateEngine(50)
+
+	for i := 0; i < b.N; i++ {
+		engine.CompileAndRender("test"+string(rune(i%10)), "Hello {{.}}", "World")
+	}
+}

tasks/board-T2.md

@@ -5,9 +5,9 @@
 | ID | Scope | Status | Branch | Verification |
 |----|-------|--------|--------|--------------|
 | T2.1 | Activity result caching: deduplicate repeated LLM calls for same task state | [x] | `task/T2.1` | Implementer called 2x on same code → second call returns cached Implementer output |
-| T2.2 | Parallel task dispatch: multiple T0.x tasks execute truly concurrently (not sequential) | [ ] | `task/T2.2` | 9 tasks complete in ~1/9 total time (wall-clock speedup measured) |
-| T2.3 | Prompt template caching: pre-compile Go templates on worker startup | [ ] | `task/T2.3` | Template render latency < 100ms (vs parse+render each time) |
-| T2.4 | Lessons file indexing: fast lookup of past failures without full file scan | [ ] | `task/T2.4` | Query lessons by task type → return in < 10ms for 1000s of entries |
+| T2.2 | Parallel task dispatch: multiple T0.x tasks execute truly concurrently (not sequential) | [x] | `task/T2.2` | 9 tasks complete in ~1/9 total time (wall-clock speedup measured) |
+| T2.3 | Prompt template caching: pre-compile Go templates on worker startup | [x] | `task/T2.3` | Template render latency < 100ms (vs parse+render each time) |
+| T2.4 | Lessons file indexing: fast lookup of past failures without full file scan | [x] | `task/T2.4` | Query lessons by task type → return in < 10ms for 1000s of entries |
 | T2.5 | Git operation batching: combine multiple worktree commits into single push/merge | [ ] | `task/T2.5` | N tasks → 1 push (vs N pushes), measured via git ref-log |
 | T2.6 | LLM request batching: group similar Implementer calls into one API request | [ ] | `task/T2.6` | 3 implementer tasks → 1 Anthropic API call with batch input (vs 3 separate calls) |
 | T2.7 | Workflow history pruning: trim old task unit outputs from orchestrator history | [ ] | `task/T2.7` | Continue-as-new cycle history size constant despite 1000s of task units completed |