# TypeScript Audit Report

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

---

## Summary

This branch refactors `handleTaskDelegated()` in DependencyHandler and `processNextTask()` in WorkerHandler into smaller, focused methods. The decomposition follows the invariants documented in `docs/architecture/HANDLER-DECOMPOSITION-INVARIANTS.md`.

**Changed Files:**
- `src/services/handlers/dependency-handler.ts` - handler method decomposition
- `src/services/handlers/worker-handler.ts` - handler method decomposition + spawn serialization
- `tests/fixtures/test-doubles.ts` - added `setEmitFailure()` helper
- `tests/unit/services/handlers/dependency-handler.test.ts` - characterization tests
- `tests/unit/services/handlers/worker-handler.test.ts` - characterization tests

---

## Issues in Your Changes (BLOCKING)

### 1. Non-null Assertion on Potentially Null Error (SHOULD FIX)

**File:** `/workspace/delegate/src/services/handlers/dependency-handler.ts`
**Lines:** 195, 207

```typescript
// Line 195
this.logger.error('Validation failed', failure.error!, context);

// Line 207
error: failure.error!
```

**Problem:** The `handleValidationFailure()` method receives a `failure` parameter with type `{ error: Error | null; type: 'ok' | 'cycle' | 'depth' | 'system' }`. The non-null assertion `!` is used on `failure.error`, but the type system shows it could be `null`.

**Analysis:** In practice, this method is only called when `failure.error !== null` (see line 309), but this invariant is not enforced by the type signature. If the calling code changes, this could cause a runtime error.

**Severity:** SHOULD FIX - The code is currently safe due to the calling convention, but the type design could be improved for better type safety.

**Recommended Fix:**
```typescript
// Option 1: Narrow the type at call site
type ValidationFailure = {
  depId: TaskId;
  error: Error;  // non-null when type !== 'ok'
  type: 'cycle' | 'depth' | 'system';
};

// Option 2: Add runtime guard
if (!failure.error) {
  this.logger.error('Unexpected null error in validation failure', undefined, context);
  return;
}
```

---

## Issues in Code You Touched (Should Fix)

### 2. Type Safety in `error as Error` Cast

**File:** `/workspace/delegate/src/services/handlers/worker-handler.ts`
**Line:** 431

```typescript
} catch (error) {
  this.logger.error('Error in task processing', error as Error);
}
```

**Problem:** The `catch` block catches `unknown` (in strict mode), but the code asserts it as `Error` without validation. If something other than an `Error` is thrown (e.g., a string, number, or custom object), this could cause unexpected behavior.

**Severity:** SHOULD FIX - This is a common pattern but does not fully adhere to strict type safety principles.

**Recommended Fix:**
```typescript
} catch (error) {
  const normalizedError = error instanceof Error ? error : new Error(String(error));
  this.logger.error('Error in task processing', normalizedError);
}
```

**Note:** This pattern also exists at lines 475 and 501, which are pre-existing (not in the diff).

---

## Pre-existing Issues (Not Blocking)

### 3. `any` Types in Test Doubles

**File:** `/workspace/delegate/tests/fixtures/test-doubles.ts`
**Lines:** 36-38, 88, 95, 132, 144, 148, 164-165, 184, 190, 350, 361, 376, 383, 468

The test doubles file contains numerous `any` types. These are pre-existing and not introduced by this branch.

```typescript
private handlers = new Map<string, Set<(event: any) => Promise<void>>>();
private requestHandlers = new Map<string, (event: any) => Promise<Result<any, Error>>>();
private emittedEvents: Array<{ type: string; payload: any; timestamp: number }> = [];
```

**Severity:** INFORMATIONAL - Test doubles often use `any` for flexibility. While not ideal, this is acceptable in test code where the focus is on behavior verification rather than strict typing.

### 4. `any` Types in MockWorkerPool

**File:** `/workspace/delegate/tests/unit/services/handlers/worker-handler.test.ts`
**Lines:** 24-30

```typescript
spawnCalls: any[] = [];
killCalls: any[] = [];
async spawn(task: any) {
```

**Severity:** INFORMATIONAL - Pre-existing issue. Mock implementations in tests commonly use `any` for simplicity.

### 5. `as any` Type Assertions in Tests

**File:** `/workspace/delegate/tests/unit/services/handlers/worker-handler.test.ts`
**Line:** 818 (NEW - in your changes)

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

**Severity:** INFORMATIONAL - This is in a characterization test that intentionally tests edge cases. Using `as any` here is pragmatic for testing empty/invalid inputs.

**File:** `/workspace/delegate/tests/unit/services/handlers/dependency-handler.test.ts`
**Line:** 719 (NEW - in your changes)

```typescript
const events = (eventBus as any).emittedEvents || [];
```

**Severity:** INFORMATIONAL - Accessing private test state. This pattern is common in tests but could be improved by exposing the property properly on the test double.

### 6. `error as Error` Patterns (Pre-existing)

**File:** `/workspace/delegate/src/services/handlers/worker-handler.ts`
**Lines:** 475, 501 (pre-existing, not in diff)

```typescript
this.logger.error('Error handling worker completion', error as Error, {...});
this.logger.error('Error handling worker timeout', err as Error, {...});
```

**Severity:** INFORMATIONAL - Same pattern as issue #2, but these are pre-existing.

---

## Code Quality Observations

### Positive Patterns Observed

1. **Strong Result Type Usage** - All handler methods properly use `Result<T, E>` types for error handling.

2. **Explicit Return Types** - All extracted methods have explicit return types:
   ```typescript
   private validateSingleDependency(...): { depId: TaskId; error: Error | null; type: ... }
   private getSpawnDelayRequired(): { shouldDelay: boolean; delayMs: number }
   private async handleValidationFailure(...): Promise<void>
   ```

3. **Generic Type Constraint** - The `withSpawnLock<T>` method properly uses generics:
   ```typescript
   private async withSpawnLock<T>(fn: () => Promise<T>): Promise<T>
   ```

4. **Readonly Arrays** - Parameter types use `readonly` modifier where appropriate:
   ```typescript
   requestedDependencies: readonly TaskId[]
   dependencies: readonly { taskId: TaskId; dependsOnTaskId: TaskId }[]
   ```

5. **Discriminated Union Types** - The validation result type uses a discriminated union:
   ```typescript
   type: 'ok' | 'cycle' | 'depth' | 'system'
   ```

---

## Summary Statistics

| Category | Count | Severity |
|----------|-------|----------|
| **Your Changes** | 1 | SHOULD FIX |
| **Code You Touched** | 1 | SHOULD FIX |
| **Pre-existing** | 6 | INFORMATIONAL |

**TypeScript Compiler:** Passes with no errors under `--strict` mode.

**TypeScript Score**: 8/10

**Deductions:**
- -1 for non-null assertion without proper type narrowing
- -1 for `error as Error` without runtime validation

---

## Merge Recommendation

**APPROVED WITH CONDITIONS**

The branch can be merged. The type safety issues identified are non-critical:

1. The non-null assertion issue (#1) is safe due to calling conventions but should be addressed in a follow-up to improve type safety.

2. The `error as Error` pattern (#2) is common in TypeScript codebases but could be hardened.

### Recommended Follow-up:
- Consider creating a type-safe validation result type that separates success/failure cases
- Normalize error handling in catch blocks project-wide

---

## Files Analyzed

| File | Status |
|------|--------|
| `/workspace/delegate/src/services/handlers/dependency-handler.ts` | MODIFIED |
| `/workspace/delegate/src/services/handlers/worker-handler.ts` | MODIFIED |
| `/workspace/delegate/tests/fixtures/test-doubles.ts` | MODIFIED |
| `/workspace/delegate/tests/unit/services/handlers/dependency-handler.test.ts` | MODIFIED |
| `/workspace/delegate/tests/unit/services/handlers/worker-handler.test.ts` | MODIFIED |
| `/workspace/delegate/docs/architecture/HANDLER-DECOMPOSITION-INVARIANTS.md` | ADDED |
