# Architecture Audit Report

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

---

## Executive Summary

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

**Overall Assessment**: The refactoring is well-executed and follows sound architectural principles. The changes are behavior-preserving, with comprehensive characterization tests ensuring safety.

---

## Changed Files Analysis

| File | Lines Changed | Purpose |
|------|---------------|---------|
| `src/services/handlers/worker-handler.ts` | +193 / -66 | Decompose processNextTask(), add spawn lock |
| `src/services/handlers/dependency-handler.ts` | +107 / -89 | Decompose handleTaskDelegated() |
| `tests/unit/services/handlers/worker-handler.test.ts` | +97 | Characterization tests for spawn serialization |
| `tests/unit/services/handlers/dependency-handler.test.ts` | +220 | Characterization tests for ordering invariants |
| `tests/fixtures/test-doubles.ts` | +9 | Add setEmitFailure() helper |
| `docs/architecture/HANDLER-DECOMPOSITION-INVARIANTS.md` | +214 | New documentation |

---

## Issues in Your Changes (BLOCKING)

**No blocking issues found.**

The refactoring maintains all behavioral invariants and the code quality is high.

---

## Issues in Code You Touched (Should Fix)

### Issue 1: Mutable State Access Across Async Boundary

**Severity**: MEDIUM  
**File**: `/workspace/delegate/src/services/handlers/worker-handler.ts`  
**Lines**: 259-270 (getSpawnDelayRequired method)

**Description**: The `getSpawnDelayRequired()` method accesses `this.lastSpawnTime` and computes `Date.now()` independently. While currently safe due to the spawn lock, this creates an implicit dependency on external synchronization that is not enforced by the type system.

**Current Code**:
```typescript
private getSpawnDelayRequired(): { shouldDelay: boolean; delayMs: number } {
  const now = Date.now();
  const timeSinceLastSpawn = now - this.lastSpawnTime;
  // ...
}
```

**Recommendation**: Consider documenting this method's precondition that it MUST be called within `withSpawnLock()`. Alternatively, make `lastSpawnTime` a parameter:
```typescript
private getSpawnDelayRequired(lastSpawnTime: number): { ... }
```

**Risk if Not Fixed**: Future developers might call this method outside the lock, reintroducing the race condition.

---

### Issue 2: setTimeout Callbacks Create Scheduling Queue

**Severity**: LOW  
**File**: `/workspace/delegate/src/services/handlers/worker-handler.ts`  
**Lines**: 284, 296

**Description**: The `handleSpawnDelayRequired()` and `handleResourcesConstrained()` methods schedule retries via `setTimeout(() => this.processNextTask(), delay)`. These scheduled callbacks accumulate outside the lock, potentially creating bursts of concurrent lock acquisitions.

**Current Code**:
```typescript
private handleSpawnDelayRequired(delayMs: number, timeSinceLastSpawn: number): void {
  // ...
  setTimeout(() => this.processNextTask(), delayMs);
}
```

**Recommendation**: This is likely acceptable for the expected load, but consider tracking pending retry timers and clearing them on teardown to prevent orphan callbacks.

---

### Issue 3: Missing JSDoc on Private Helper Methods

**Severity**: LOW  
**File**: `/workspace/delegate/src/services/handlers/dependency-handler.ts`  
**Lines**: 143-179, 186-209, 215-229

**Description**: The extracted methods have documentation comments but could benefit from explicit `@param` and `@returns` JSDoc annotations for consistency with the rest of the codebase.

**Recommendation**: Add full JSDoc with `@param` and `@returns` for IDE support:
```typescript
/**
 * Validate a single dependency - check for cycles and depth limits
 * @param taskId - The task to add the dependency to
 * @param depId - The task to depend on
 * @returns Validation result with type indicating: ok, cycle, depth, or system error
 */
```

---

## Pre-existing Issues (Not Blocking)

### Pre-existing Issue 1: No Integration Test for Spawn Lock Under Contention

**Severity**: INFORMATIONAL  
**File**: N/A (test gap)

**Description**: The characterization tests verify the lock semantics in unit tests with mocks, but there is no integration test that exercises the lock under real concurrent load with actual process spawning.

**Recommendation**: Consider adding an integration test in a future PR that:
1. Submits multiple tasks simultaneously
2. Verifies that spawns are serialized (measured by spawn timestamps)
3. Verifies no fork bomb occurs even with rapid task submission

---

### Pre-existing Issue 2: resourceMonitor.recordSpawn() is NO-OP in TestResourceMonitor

**Severity**: INFORMATIONAL  
**File**: `/workspace/delegate/tests/fixtures/test-doubles.ts`  
**Lines**: 542-547

**Description**: The test double explicitly documents this as intentional, but it means tests cannot verify that settling worker tracking works correctly.

**Current Code**:
```typescript
recordSpawn(): void {
  // INTENTIONAL NO-OP: Test double doesn't track settling workers
}
```

**Recommendation**: This is acceptable for current tests, but consider adding a separate test that verifies recordSpawn() integration with the real ResourceMonitor.

---

### Pre-existing Issue 3: Redundant EventBus Field in DependencyHandler

**Severity**: INFORMATIONAL  
**File**: `/workspace/delegate/src/services/handlers/dependency-handler.ts`  
**Lines**: 28, 43

**Description**: The `eventBus` is stored as both a private field (`this.eventBus`) and available via the parent class `BaseEventHandler`. This is pre-existing but creates potential confusion.

---

## Architecture Analysis

### SOLID Principles

| Principle | Assessment | Notes |
|-----------|------------|-------|
| **S**ingle Responsibility | GOOD | Extracted methods have clear, focused responsibilities |
| **O**pen/Closed | GOOD | Decomposition enables extension without modification |
| **L**iskov Substitution | N/A | No inheritance hierarchies affected |
| **I**nterface Segregation | GOOD | No changes to interfaces |
| **D**ependency Inversion | GOOD | Dependencies remain injected |

### Design Pattern Usage

1. **Method Extraction (Refactoring Pattern)**: Correctly applied. Each extracted method handles one concern:
   - `getSpawnDelayRequired()` - Pure calculation
   - `handleSpawnDelayRequired()` - Side effect (scheduling)
   - `validateSingleDependency()` - Pure validation
   - `handleValidationFailure()` - Side effect (logging + events)

2. **Mutex Pattern (Spawn Lock)**: Well-implemented promise-chain mutex:
   ```typescript
   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;
     await previousLock;
     try {
       return await fn();
     } finally {
       releaseLock();
     }
   }
   ```
   This is a lightweight, correct implementation that avoids external dependencies.

3. **Orchestration Pattern**: The main methods (`processNextTask`, `handleTaskDelegated`) now act as orchestrators that delegate to specialized helpers.

### Separation of Concerns

| Layer | Responsibility | Maintained? |
|-------|----------------|-------------|
| Handler | Orchestration, event handling | YES |
| Extracted Methods | Specific operations | YES |
| Repository | Data persistence | YES |
| EventBus | Communication | YES |

### Dependency Analysis

**No circular dependencies detected.** Import graph remains acyclic:
- `worker-handler.ts` imports from `core/` only
- `dependency-handler.ts` imports from `core/` only
- No handlers import from each other

### Invariant Preservation

The refactoring correctly preserves all documented invariants:

1. **Spawn delay check FIRST** - Line 381-387 in `processNextTask()`
2. **Resource check SECOND** - Line 389-394 in `processNextTask()`
3. **All validations run in PARALLEL** - Line 303-305 via `Promise.all()`
4. **Database write AFTER all validations** - Line 315
5. **Graph update AFTER successful database write** - Line 328
6. **Events emitted AFTER graph update** - Line 331

---

## Test Coverage Analysis

### Characterization Tests Added

| Test | Purpose | File |
|------|---------|------|
| Spawn serialization prevents overlap | Verify mutex | worker-handler.test.ts:880 |
| TOCTOU race prevented by lock | Verify delay check inside lock | worker-handler.test.ts:926 |
| TaskStarting failure requeues without TaskFailed | Invariant preservation | worker-handler.test.ts:694 |
| Validation failure prevents database writes | Atomicity | dependency-handler.test.ts:752 |
| Graph update AFTER DB write | Ordering invariant | dependency-handler.test.ts:780 |

### Test Results

```
Test Files  2 passed (2)
     Tests  43 passed (43)
```

All handler tests pass, including the new characterization tests.

---

## Summary

### Your Changes

| Severity | Count |
|----------|-------|
| BLOCKING | 0 |
| MEDIUM | 1 |
| LOW | 2 |

### Code You Touched

| Severity | Count |
|----------|-------|
| MEDIUM | 1 (mutable state access pattern) |
| LOW | 2 (setTimeout queue, JSDoc) |

### Pre-existing

| Severity | Count |
|----------|-------|
| INFORMATIONAL | 3 (test gap, test double NO-OP, redundant field) |

---

## Architecture Score: 9/10

**Positive Factors**:
- Clean decomposition following Single Responsibility
- Correct mutex implementation for TOCTOU fix
- Comprehensive characterization tests
- Excellent documentation of invariants
- No new coupling or circular dependencies
- Behavior-preserving refactoring

**Deduction (-1)**:
- Minor documentation gaps in extracted methods
- Implicit precondition on spawn lock not type-enforced

---

## Merge Recommendation

### APPROVED

This refactoring is well-executed and safe to merge. The spawn serialization fix addresses a real race condition, and the decomposition improves code maintainability without changing behavior.

**Pre-merge Checklist**:
- [x] All existing tests pass
- [x] New characterization tests provide safety net
- [x] Ordering invariants documented and preserved
- [x] Atomicity invariants preserved
- [x] Error handling paths unchanged
- [x] No new circular dependencies
- [x] No blocking architecture issues

**Optional Improvements (can be done post-merge)**:
- Add full JSDoc to extracted methods
- Consider tracking pending setTimeout callbacks for clean teardown
