# Architecture Audit Report

**Branch**: feature/incremental-graph-updates
**Base**: main
**Date**: 2025-11-21 06:24:00
**Files Changed**: 9
**Lines**: +880, -286

---

## Executive Summary

This PR refactors dependency graph management from a cache-invalidation pattern to an incremental-update pattern. The key architectural change moves graph ownership from `DependencyRepository` (with cache invalidation) to `DependencyHandler` (with incremental updates).

**Overall Assessment**: APPROVED WITH CONDITIONS

The architectural change is sound and follows established patterns in the codebase. The separation of concerns is improved, with the repository becoming a pure data access layer. However, there are a few issues that should be addressed.

---

## 1. Issues in Your Changes (BLOCKING)

### 1.1 MEDIUM: Depth Validation Removed Without Replacement

**File**: `/workspace/delegate/src/implementations/dependency-repository.ts`
**Lines**: 219-221 (comment indicates removal)

**Issue**: The depth validation (`MAX_DEPENDENCY_CHAIN_DEPTH`) was removed from the repository but NOT moved to the handler. The constant still exists (line 18) but is now dead code.

**Before (main branch)**:
```typescript
// SECURITY: Check dependency chain depth to prevent stack overflow
const resultingDepth = 1 + maxDependencyDepth;
if (resultingDepth > SQLiteDependencyRepository.MAX_DEPENDENCY_CHAIN_DEPTH) {
  throw new DelegateError(
    ErrorCode.INVALID_OPERATION,
    `Cannot add dependencies: would create dependency chain depth of ${resultingDepth}...`
  );
}
```

**After (this branch)**:
```typescript
// NOTE: Cycle detection and depth checking removed
// ARCHITECTURE: Business logic (DAG validation) moved to DependencyHandler
// Repository is now pure data access layer
```

**Problem**: The handler performs cycle detection but does NOT perform depth checking. This is a security regression - deep dependency chains could cause stack overflow in cycle detection DFS.

**Evidence**: Searching the handler shows no `getMaxDepth` call or depth validation:
- Handler performs cycle detection (lines 104-136)
- Handler does NOT perform depth validation
- `DependencyGraph.getMaxDepth()` exists but is unused in the new flow

**Impact**: Security vulnerability - DoS via extremely deep dependency chains.

**Fix Required**: Add depth validation to `DependencyHandler.handleTaskDelegated()` before the cycle check loop:
```typescript
// Before cycle detection, check depth limits
const maxDepth = this.graph.getMaxDepth(depId);
if (maxDepth >= MAX_DEPENDENCY_CHAIN_DEPTH - 1) {
  // Reject - would exceed max depth
}
```

---

### 1.2 LOW: Dead Code - Unused Constants

**File**: `/workspace/delegate/src/implementations/dependency-repository.ts`
**Lines**: 17-18

```typescript
// SECURITY: Hard limits to prevent DoS attacks and stack overflow
private static readonly MAX_DEPENDENCIES_PER_TASK = 100;
private static readonly MAX_DEPENDENCY_CHAIN_DEPTH = 100;  // <-- DEAD CODE
```

**Issue**: `MAX_DEPENDENCY_CHAIN_DEPTH` is no longer used after removing depth validation. Either move it to the handler or delete it.

**Impact**: Code confusion, maintainability issue.

---

## 2. Issues in Code You Touched (SHOULD FIX)

### 2.1 MEDIUM: Graph Update Not Called on Dependency Deletion

**File**: `/workspace/delegate/src/implementations/dependency-repository.ts`
**Lines**: 531-545

```typescript
async deleteDependencies(taskId: TaskId): Promise<Result<void>> {
  return tryCatchAsync(
    async () => {
      // Delete from database (removes edges, NOT the task node itself)
      this.deleteDependenciesStmt.run(taskId, taskId);

      // NOTE: Graph updates removed
      // ARCHITECTURE: DependencyHandler now owns graph and handles updates via events
    },
    ...
  );
}
```

**Issue**: The repository deletes dependencies from the database, but there is no corresponding graph update mechanism. The handler subscribes to task lifecycle events (TaskCompleted, TaskFailed, etc.) but NOT to a "TaskDeleted" or "DependenciesDeleted" event.

**Analysis**:
1. When `deleteDependencies()` is called (e.g., during task cancellation), database is updated
2. The handler's in-memory graph is NOT updated
3. The `removeTask()` method exists in `DependencyGraph` but is never called

**Impact**: Graph-database desynchronization after task deletion.

**Current Event Flow**:
- TaskCancelled -> handler calls `resolveDependencies()` -> resolves dependencies (marks as cancelled)
- BUT: If task is DELETED (not just cancelled), graph becomes stale

**Recommendation**: Either:
1. Add a `TaskDeleted` event that handler listens to and calls `this.graph.removeTask()`
2. OR ensure `deleteDependencies()` is only called in contexts where the handler already updates graph

---

### 2.2 LOW: Inconsistent Error Handling Pattern

**File**: `/workspace/delegate/src/services/handlers/dependency-handler.ts`
**Lines**: 106-136

**Issue**: The handler performs cycle detection in a loop but returns on first failure. However, it emits `TaskDependencyFailed` event only for the failing dependency, not indicating that the entire batch was rejected.

```typescript
for (const depId of task.dependsOn) {
  const cycleCheck = this.graph.wouldCreateCycle(task.id, depId);
  // ...
  if (cycleCheck.value) {
    // Emits event for THIS dependency only
    await this.eventBus.emit('TaskDependencyFailed', {
      taskId: task.id,
      failedDependencyId: depId,  // Only this one
      error
    });
    return err(error);  // Entire batch rejected
  }
}
```

**Suggestion**: Consider emitting a batch-level failure event that includes all requested dependencies, making it clearer that the entire operation failed, not just one dependency.

---

### 2.3 LOW: Missing Logging for Removed Event Subscription

**File**: `/workspace/delegate/src/services/handlers/dependency-handler.ts`
**Line**: 66

```typescript
// NOTE: No longer subscribe to TaskDependencyAdded - we update graph directly
```

**Issue**: Good architecture decision, but the initialization log (line 76) should be updated to reflect this change. Currently it says "DAG validation and dependency tracking active" but doesn't indicate the new incremental update pattern.

**Suggestion**: Update log message to reflect the new architecture.

---

## 3. Pre-existing Issues (INFORMATIONAL)

### 3.1 INFO: Race Condition Window in Event-Driven Pattern

**File**: `/workspace/delegate/src/services/handlers/dependency-handler.ts`
**Lines**: 139-176

```typescript
// All cycle checks passed - persist to database
const addResult = await this.dependencyRepo.addDependencies(task.id, task.dependsOn);
// ... error handling ...

// CRITICAL: Update handler's graph AFTER successful database operation
for (const dependency of addResult.value) {
  this.graph.addEdge(dependency.taskId, dependency.dependsOnTaskId);
}
```

**Observation**: Between the database write and graph update, there's a small window where another event could query the (now stale) graph. This is an inherent limitation of eventual consistency in event-driven systems.

**Mitigation**: The codebase uses synchronous SQLite transactions which block the event loop, so this window is minimized. The comment "CRITICAL: Update handler's graph AFTER successful database operation" correctly documents this.

**Status**: Pre-existing architectural trade-off, properly documented.

---

### 3.2 INFO: Test Timing Dependencies

**File**: `/workspace/delegate/tests/unit/services/handlers/dependency-handler.test.ts`
**Multiple locations**: Uses `setTimeout(resolve, 50)` for event propagation.

```typescript
await new Promise(resolve => setTimeout(resolve, 50));
```

**Observation**: Tests use fixed delays for event propagation. This is a common pattern but can cause flaky tests on slow systems.

**Status**: Pre-existing, not introduced by this PR.

---

## 4. Architectural Analysis

### 4.1 Is Moving Graph Ownership to Handler the Right Design?

**VERDICT: YES** - This is the correct architectural decision.

**Rationale**:

1. **Separation of Concerns**: 
   - Repository: Pure data access (CRUD operations on SQLite)
   - Handler: Business logic (DAG validation, cycle detection, depth limits)
   - Graph: In-memory data structure with algorithms

2. **Single Responsibility**:
   - Repository no longer manages graph cache (was mixing data access with caching)
   - Handler owns the graph because it's the component that needs it for business logic

3. **Performance**:
   - Eliminates N+1 `findAll()` queries (70-80% latency improvement claimed)
   - One-time O(N) initialization, then O(1) incremental updates
   - Graph is kept hot in memory, not rebuilt from database on each operation

4. **Consistency with Event-Driven Architecture**:
   - Handler already owns the event-driven logic
   - Graph updates happen in same transaction context as business logic
   - Events flow through handler, so handler is natural owner

### 4.2 Is Repository Now Purely Data Layer?

**VERDICT: MOSTLY YES** - Minor cleanup needed.

**What's Good**:
- No more `DependencyGraph` import or usage
- No more cache management
- Pure SQL operations via prepared statements
- All validation is parameter validation, not business logic

**What Needs Cleanup**:
- `MAX_DEPENDENCY_CHAIN_DEPTH` constant is now dead code (see Issue 1.2)
- Depth validation logic was removed but not moved (see Issue 1.1)

### 4.3 Are Events Being Used Correctly?

**VERDICT: MOSTLY YES** - One gap identified.

**Correct Event Usage**:
- `TaskDelegated` -> Handler adds dependencies + updates graph
- `TaskCompleted/Failed/Cancelled/Timeout` -> Handler resolves dependencies
- `TaskDependencyAdded` -> Handler no longer subscribes (correct, updates graph directly)

**Gap**:
- No event for task deletion that would trigger `graph.removeTask()` (see Issue 2.1)

### 4.4 Consistency with Project's Established Patterns

**VERDICT: YES** - Follows established patterns.

**Result Pattern**: Used consistently throughout
```typescript
async setup(eventBus: EventBus): Promise<Result<void>> {
  // ...
  if (!allDepsResult.ok) {
    return err(allDepsResult.error);
  }
```

**Event-Driven Architecture**: Extended correctly
- Handler subscribes to events
- Handler emits events after operations
- No direct coupling between components

**Immutability**: Graph methods return new arrays, don't mutate inputs
```typescript
return ok(Array.from(deps) as TaskId[]);
```

**Dependency Injection**: Repository injected into handler
```typescript
constructor(
  private readonly dependencyRepo: DependencyRepository,
  private readonly taskRepo: TaskRepository,
  logger: Logger
)
```

---

## 5. Summary

### Your Changes (Lines Added/Modified):

| Severity | Count | Description |
|----------|-------|-------------|
| MEDIUM   | 1     | Depth validation removed but not moved to handler |
| LOW      | 1     | Dead code (unused constant) |

### Code You Touched (Functions/Modules Modified):

| Severity | Count | Description |
|----------|-------|-------------|
| MEDIUM   | 1     | Graph not updated on dependency deletion |
| LOW      | 2     | Inconsistent error handling, missing log update |

### Pre-existing (Files Reviewed But Not Modified):

| Severity | Count | Description |
|----------|-------|-------------|
| INFO     | 2     | Race condition window (documented), test timing |

### Architecture Score: 8/10

**Deductions**:
- -1: Missing depth validation (security regression)
- -1: Missing graph update on deletion (sync issue)

---

## 6. Merge Recommendation

**APPROVED WITH CONDITIONS**

The architectural changes are sound and well-implemented. The refactoring correctly separates concerns and improves performance.

**Before Merge**:
1. **MUST FIX**: Add depth validation to `DependencyHandler.handleTaskDelegated()` - this is a security regression
2. **SHOULD FIX**: Either add `TaskDeleted` event handling or document that `deleteDependencies()` usage context already handles graph updates
3. **OPTIONAL**: Remove dead `MAX_DEPENDENCY_CHAIN_DEPTH` constant from repository

**After These Fixes**: APPROVED for merge.

---

## 7. Test Coverage Assessment

The PR includes comprehensive tests for the new incremental update functionality:

**New Tests Added**:
- `dependency-graph.test.ts`: 18+ tests for `addEdge()`, `removeEdge()`, `removeTask()`
- Memory leak prevention tests
- Cycle detection integration tests
- `dependency-handler.test.ts`: Graph consistency tests

**Test Quality**: Good - tests verify behavior, not implementation details.

**Gap**: No test for the missing depth validation (because validation was removed without replacement).

---

*Generated by Architecture Audit Specialist*
*Report Location: `.docs/audits/feature-incremental-graph-updates/architecture-report.2025-11-21_0624.md`*
