# Complexity Audit Report

**Branch**: refactor/decompose-large-handlers
**Base**: main
**Date**: 2025-12-06 22:00

---

## Executive Summary

This branch decomposes two large handler methods (`handleTaskDelegated()` in DependencyHandler and `processNextTask()` in WorkerHandler) into smaller, focused methods. Additionally, it introduces spawn serialization to fix a TOCTOU race condition that could cause fork bombs.

**Overall Assessment**: This is a well-executed refactoring that **reduces** complexity by extracting single-responsibility methods from monolithic functions. The new `withSpawnLock()` mutex pattern adds essential thread safety.

---

## RED: Issues in Your Changes (BLOCKING)

**NONE FOUND**

The refactoring follows best practices for method extraction:
- Extracted methods are pure or have single responsibilities
- Ordering invariants are preserved
- Atomicity requirements are maintained
- No new complexity introduced - complexity is reduced through decomposition

---

## YELLOW: Issues in Code You Touched (Should Fix)

### 1. Synchronous validateSingleDependency() in Async Context

**File**: `/workspace/delegate/src/services/handlers/dependency-handler.ts`
**Lines**: 143-180
**Severity**: MEDIUM

The `validateSingleDependency()` method is synchronous but is called inside `Promise.all()` via `.map()`. While this works correctly (sync functions wrapped in Promise.all still execute), the pattern is misleading:

```typescript
// Line 303-305 - Current implementation
const validationResults = await Promise.all(
  task.dependsOn.map(depId => this.validateSingleDependency(task.id, depId))
);
```

**Issue**: The original code used `async` for each validation:
```typescript
// Original code had async (depId) => { ... }
```

The refactored version removed `async` which is fine, but the JSDoc says "PURE: Read-only operation" while the method accesses `this.graph` state.

**Recommendation**: Either:
1. Mark the method as `async` for consistency with Promise.all pattern, OR
2. Update the JSDoc to clarify it's synchronous but thread-safe for concurrent execution

**Impact**: Low - code works correctly, this is a documentation/clarity issue.

---

### 2. Potential Promise Chain Memory Leak in spawnLock

**File**: `/workspace/delegate/src/services/handlers/worker-handler.ts`
**Lines**: 225-248 (`withSpawnLock`)
**Severity**: LOW

The spawn lock uses promise chaining for mutex behavior. Each call creates a new promise:

```typescript
private spawnLock: Promise<void> = Promise.resolve();

private async withSpawnLock<T>(fn: () => Promise<T>): Promise<T> {
  const previousLock = this.spawnLock;
  let releaseLock!: () => void;
  const ourLock = new Promise<void>(resolve => {
    releaseLock = resolve;
  });
  this.spawnLock = ourLock;  // Chains grow indefinitely
  // ...
}
```

**Issue**: If many spawn attempts occur without the handler being recreated, the promise chain grows. Each resolved promise in the chain retains a small amount of memory.

**Mitigation**: This is acceptable because:
1. Worker handlers are recreated on server restart
2. Spawn rate is limited (10s minimum delay)
3. Memory per promise is minimal (~48 bytes)

**Recommendation**: No immediate action needed. Consider documenting this behavior in the handler lifecycle documentation.

---

### 3. Non-Null Assertion on failure.error

**File**: `/workspace/delegate/src/services/handlers/dependency-handler.ts`
**Lines**: 186-209
**Severity**: LOW

```typescript
private async handleValidationFailure(
  taskId: TaskId,
  requestedDependencies: readonly TaskId[],
  failure: { depId: TaskId; error: Error | null; type: 'ok' | 'cycle' | 'depth' | 'system' }
): Promise<void> {
  // ...
  this.logger.error('Validation failed', failure.error!, context);  // Line 195
  // ...
  error: failure.error!  // Line 207
```

**Issue**: The type allows `error: null` but the code uses `!` to assert non-null. While the call site in `handleTaskDelegated()` checks for `failure.error !== null` before calling, the method signature doesn't guarantee this.

**Recommendation**: Change the parameter type to exclude the 'ok' case:
```typescript
failure: { depId: TaskId; error: Error; type: 'cycle' | 'depth' | 'system' }
```

---

## INFO: Pre-existing Issues (Not Blocking)

### 1. resolveDependencies() Remains Complex (Pre-existing)

**File**: `/workspace/delegate/src/services/handlers/dependency-handler.ts`
**Lines**: 401-505
**Severity**: MEDIUM (Pre-existing)
**Cyclomatic Complexity**: ~8

This method was NOT refactored in this branch but has similar complexity to the refactored methods:
- Nested conditionals (lines 457-460, 476-481, 489-495)
- Multiple early returns
- Loop with multiple async operations

**Not blocking**: This is pre-existing complexity. Consider refactoring in a follow-up PR.

---

### 2. handleTaskCancellation() Has Deep Nesting (Pre-existing)

**File**: `/workspace/delegate/src/services/handlers/worker-handler.ts`  
**Lines**: 131-202
**Severity**: LOW (Pre-existing)
**Nesting Depth**: 4 levels

This method contains:
- 4 levels of nesting (if within if within handleEvent within method)
- Multiple early returns within nested blocks

**Not blocking**: Pre-existing, not touched by this refactor.

---

### 3. Test File Uses Type Coercion

**File**: `/workspace/delegate/tests/unit/services/handlers/worker-handler.test.ts`
**Lines**: 818
**Severity**: LOW

```typescript
await eventBus.emit('TaskQueued', { taskId: 'test' as any, task: {} as any });
```

**Issue**: Test uses `as any` to bypass type checking.

**Not blocking**: Test code, not production. Acceptable for testing edge cases.

---

## Positive Changes (Complexity Reduction)

### 1. handleTaskDelegated() Decomposition - EXCELLENT

**Before**: 130 lines, cyclomatic complexity ~12
**After**: 50 lines in orchestrator + 5 focused helper methods

Extracted methods with single responsibilities:
| Method | Lines | Purpose | Complexity |
|--------|-------|---------|------------|
| `validateSingleDependency()` | 38 | Pure validation | 4 |
| `handleValidationFailure()` | 24 | Logging + event | 3 |
| `handleDatabaseFailure()` | 16 | Error handling | 1 |
| `updateGraphAfterPersistence()` | 19 | Graph update | 2 |
| `emitDependencyAddedEvents()` | 11 | Event emission | 1 |
| `handleTaskDelegated()` | 50 | Orchestration | 4 |

**Net result**: Cyclomatic complexity reduced from ~12 to max 4 per method.

---

### 2. processNextTask() Decomposition - EXCELLENT

**Before**: 90 lines, cyclomatic complexity ~10
**After**: 58 lines in orchestrator + 6 focused helper methods

Extracted methods:
| Method | Lines | Purpose | Complexity |
|--------|-------|---------|------------|
| `withSpawnLock()` | 24 | Mutex pattern | 1 |
| `getSpawnDelayRequired()` | 13 | Pure calculation | 2 |
| `handleSpawnDelayRequired()` | 9 | Retry scheduling | 1 |
| `handleResourcesConstrained()` | 8 | Backoff handling | 1 |
| `handleTaskStartingFailure()` | 8 | Error handling | 1 |
| `handleSpawnFailure()` | 16 | Error + requeue | 1 |
| `recordSpawnSuccessAndEmitEvents()` | 26 | Success path | 1 |
| `processNextTask()` | 58 | Orchestration | 6 |

**Net result**: Cyclomatic complexity reduced from ~10 to max 6 per method.

---

### 3. Added Comprehensive Characterization Tests - EXCELLENT

**Files Modified**:
- `/workspace/delegate/tests/unit/services/handlers/dependency-handler.test.ts` (+232 lines)
- `/workspace/delegate/tests/unit/services/handlers/worker-handler.test.ts` (+331 lines)

New test categories:
- Ordering invariants (7 tests)
- State consistency invariants (2 tests)
- Spawn serialization (3 tests)
- Atomicity invariants (2 tests)
- Error type classification (2 tests)

These tests document critical invariants that must be preserved in future refactoring.

---

### 4. Added Architecture Documentation - EXCELLENT

**File**: `/workspace/delegate/docs/architecture/HANDLER-DECOMPOSITION-INVARIANTS.md` (+214 lines)

Documents:
- Spawn serialization rationale and mechanism
- Ordering invariants for both handlers
- Error handling requirements
- Safe vs dangerous extraction patterns
- Verification checklist for future work

---

## Summary

### Your Changes:

| Severity | Count | Details |
|----------|-------|---------|
| BLOCKING | 0 | None |
| SHOULD FIX | 3 | Type signature clarity, documentation |
| INFORMATIONAL | 0 | N/A |

### Pre-existing:

| Severity | Count | Details |
|----------|-------|---------|
| MEDIUM | 1 | resolveDependencies() complexity |
| LOW | 2 | Nesting depth, test type coercion |

### Complexity Metrics

| Metric | Before | After | Change |
|--------|--------|-------|--------|
| Max method length (DependencyHandler) | 130 lines | 50 lines | -62% |
| Max method length (WorkerHandler) | 90 lines | 58 lines | -36% |
| Max cyclomatic complexity | 12 | 6 | -50% |
| Number of methods with CC > 10 | 2 | 0 | -100% |
| Test coverage (estimated) | 80% | 85%+ | +5% |

---

## Complexity Score: 8/10

**Rationale**: 
- Started at 6/10 (monolithic handlers with high complexity)
- Now at 8/10 (decomposed, well-documented, thoroughly tested)
- Deductions: Minor type signature issues, pre-existing complexity in untouched methods

---

## Merge Recommendation: APPROVED

**Conditions**: None required. The SHOULD FIX items are minor and can be addressed in follow-up PRs.

**Justification**:
1. No blocking issues found
2. Complexity reduced significantly (50% reduction in max cyclomatic complexity)
3. New spawn serialization fixes a real race condition (TOCTOU)
4. Excellent test coverage with characterization tests
5. Comprehensive architecture documentation added
6. All existing tests must pass (verify in CI)

---

## Files Changed

| File | Lines Changed | Type |
|------|--------------|------|
| `src/services/handlers/dependency-handler.ts` | +147 / -98 | Refactor |
| `src/services/handlers/worker-handler.ts` | +189 / -82 | Refactor + Fix |
| `tests/fixtures/test-doubles.ts` | +15 | Test infrastructure |
| `tests/unit/services/handlers/dependency-handler.test.ts` | +232 | Tests |
| `tests/unit/services/handlers/worker-handler.test.ts` | +331 | Tests |
| `docs/architecture/HANDLER-DECOMPOSITION-INVARIANTS.md` | +214 | Documentation |

**Total**: +1128 / -180 lines (net +948 lines, primarily tests and documentation)
