# Arbiter → Apophis Feedback Report

**Date:** 2026-04-27
**Reporter:** Arbiter Engineering Team
**Context:** Integration of Apophis v2.2 into Arbiter Platform for behavioral contract testing

---

## Executive Summary

Apophis provides genuinely valuable capabilities for behavioral contract testing that go beyond traditional unit/integration tests. The schema-to-contract inference, cross-operation verification, and chaos testing infrastructure are compelling. However, we encountered 3 bugs in core infrastructure and several design friction points that should be addressed for wider adoption.

**Overall Assessment:** Strong value proposition for teams willing to invest in schema-driven testing. Needs polish on edge cases and configurability.

---

## Part 1: How Chaos Injection Would Help Arbiter

### Current State
Arbiter is a multi-tenant SaaS platform with:
- 500+ API endpoints across 15 route families
- Billing, graph storage, auth, sessions, webhooks, etc.
- Mock Stripe integration for payment processing
- In-memory and persistent storage backends
- Complex middleware chain: auth → tenant boundary → permissions → preflight → handler

### Where Chaos Testing Adds Value

**1. Middleware Resilience Verification**

Our middleware chain has implicit dependencies:
```
Transport → AuthN → Scope → AuthZ → Challenge → Preflight → Handler
```

Chaos testing would verify:
- What happens when `preflight()` times out? Does the handler still execute?
- If auth middleware fails with 503, do we get proper retry headers?
- Does a slow tenant boundary check cascade to response timeouts?

**Concrete scenario:** If the billing preflight gate (budget check) is slow, does the subscription creation handler wait or fail? Our contracts say `response_time < 2000ms` — chaos would tell us if that's actually enforced.

**2. Mock Service Degradation**

We use `MockStripeService` for payment processing. In production, Stripe can:
- Return 429 (rate limit)
- Time out on `paymentIntents.create`
- Return network errors

Chaos testing would inject:
```
if chaos:stripe-timeout then response_code == 503
if chaos:stripe-rate-limit then retry-after header != null
```

This validates our fallback logic — currently untested because mocks always succeed.

**3. Resource Leak Detection**

Our `BillingApplicationService` uses in-memory Maps. Chaos scenarios:
- Create 1000 plans, delete 500, verify GET on deleted returns 404
- Cancel subscriptions mid-renewal cycle
- Concurrent PATCH operations on same plan

Cross-operation contracts catch this for single requests, but chaos tests concurrent state corruption.

**4. Entitlement Boundary Testing**

We have credit-based preflight gates. Chaos could:
- Exhaust credits mid-test
- Verify 402 (Payment Required) is returned
- Ensure no partial mutations occur when budget is depleted

This is business-critical: we cannot bill customers for operations that fail.

**5. Auth Token Expiry**

JWT tokens expire. Chaos could:
- Expire tokens between POST and follow-up GET
- Verify 401 with proper `WWW-Authenticate` header
- Test refresh token flow under load

### Proposed Chaos Scenarios for Arbiter

```yaml
billing_chaos:
  - name: stripe-timeout
    target: POST /billing/invoices/:id/pay
    inject: { stripe_delay_ms: 5000 }
    expected: { status: 503, retry_after: "> 0" }
  
  - name: storage-corruption
    target: DELETE /billing/plans/:id
    inject: { skip_deletion: true }
    expected: { status: 200, follow_up_get: 404 }
  
  - name: rate-limit
    target: POST /billing/plans
    inject: { rate_limit: 10 }
    expected: { status: 429, x_retry_after: "> 0" }
  
  - name: auth-expiry
    target: PATCH /billing/plans/:id
    inject: { expire_token_after_ms: 100 }
    expected: { status: 401, www_authenticate: "Bearer" }
```

---

## Part 2: Bugs Found

### Bug 1: Scope Registry Ignores Configured Default Scope

**Severity:** High (breaks auth in cross-operation tests)
**File:** `dist/infrastructure/scope-registry.js`
**Line:** 60, 76-77

**Problem:**
```javascript
const scope = scopeName !== null ? this.scopes.get(scopeName) : undefined;
const base = scope ?? this.defaultScope;  // Always uses empty DEFAULT_SCOPE
```

When `getHeaders(null)` is called, it uses `this.defaultScope` which is initialized to `{ headers: {}, metadata: {} }` on line 60, ignoring any "default" scope passed in the constructor.

**Impact:** Cross-operation requests (e.g., `response_code(GET /users/{id})`) don't inherit auth headers from the configured scope, causing 401 failures on protected routes.

**Fix:**
```javascript
const base = scope ?? this.scopes.get('default') ?? this.defaultScope;
```

**Reproduction:**
```javascript
await app.register(apophis, {
  scopes: {
    default: { headers: { 'authorization': 'Bearer token' } }
  }
});
// Cross-operation GET /users/123 gets 401 because auth header is not passed
```

### Bug 2: Contract Builder Drops Routes Option

**Severity:** High (route filtering doesn't work)
**File:** `dist/plugin/contract-builder.js`
**Line:** 8-15

**Problem:**
```javascript
const config = {
    depth: opts.depth ?? 'standard',
    scope: opts.scope,
    seed: opts.seed,
    timeout: opts.timeout,
    chaos: opts.chaos,
    // Missing: routes: opts.routes
};
```

The `routes` option is documented but never passed to `runPetitTests`, causing all routes to be tested regardless of the `routes` filter.

**Impact:** Tests run against all 500+ routes instead of the 4 specified, making debugging impossible and CI times explode.

**Fix:**
```javascript
const config = {
    depth: opts.depth ?? 'standard',
    scope: opts.scope,
    seed: opts.seed,
    timeout: opts.timeout,
    chaos: opts.chaos,
    routes: opts.routes,  // Add this
};
```

**Reproduction:**
```javascript
await app.apophis.contract({
  routes: ['POST /billing/plans']  // Tests ALL routes instead
});
```

### Bug 3: Invariant Checking Not Configurable

**Severity:** Medium (false failures for non-hierarchical APIs)
**File:** `dist/test/petit-runner.js`
**Line:** 386-398

**Problem:** Built-in invariants (`no-orphaned-resources`, `parent-reference-integrity`, `resource-integrity`) run unconditionally for all routes. These assume parent-child resource hierarchies (e.g., `/workspaces/:id/projects/:id`).

**Impact:** For flat resource models (like our billing plans), routes with `x-category: 'constructor'` trigger invariant failures because resources don't have `parentType`/`parentId`.

**Workaround:** We set `x-category: 'observer'` to avoid resource tracking, but this loses the semantic meaning of the route.

**Suggested Fix:**
```javascript
// In config
invariants: ['resource-integrity']  // Opt-in per test
// Or
invariants: false  // Disable all
// Or per-route
schema: {
  'x-invariants': ['custom-only']
}
```

---

## Part 3: Design Feedback

### 1. Schema Inference is Too Aggressive

**Issue:** `const` values in JSON Schema generate unconditional contracts.

Example:
```json
{
  "response": {
    "200": {
      "properties": {
        "fragment_type": { "const": "Action" }
      }
    }
  }
}
```

Generates: `response_body(this).fragment_type == "Action"` (checked for ALL responses)

This fails when the route returns 404 with `fragment_type: "Error"`.

**Suggestion:** Infer conditional contracts based on status code:
```
if status:200 then response_body(this).fragment_type == "Action" else true
```

Or add an option to disable inference: `inferContracts: false`.

### 2. Cross-Operation Headers Not Documented

The `scope.headers` behavior for cross-operation requests is not documented. We had to read source code to discover that:
- `createOperationResolver(fastify, request.headers)` passes request headers
- But `request.headers` comes from `scope.getHeaders(null)`
- Which had bug #1 above

**Suggestion:** Document that cross-operation requests inherit the scope headers of the original request.

### 3. Missing 400 Response Handling

When Fastify schema validation fails (e.g., enum mismatch), it returns 400 with a validation error object. Apophis treats this as a contract failure unless:
- The schema has a 400 response documented
- The contract explicitly accepts 400

Most developers won't document 400 responses. Apophis should either:
- Auto-generate 400 contracts from validation rules
- Or provide a global 400 handler pattern

### 4. HEAD Routes Cause Noise

Fastify auto-generates HEAD routes for every GET. These have no response body, causing `response_body(this).id != null` failures.

**Suggestion:** Auto-skip HEAD routes in contract tests, or provide `skipMethods: ['HEAD']` option.

### 5. Error Suggestions Need Context

When a contract fails, the error is:
```
Field 'fragment_type' does not match expected value 'Error'.
```

But it doesn't say:
- What the actual status code was
- What the actual response body was
- Which route generated the request

**Suggestion:** Include actual vs expected in violation objects.

---

## Part 4: What We Love

### 1. Cross-Operation Contracts

```
if status:201 then response_code(GET /billing/plans/{response_body(this).data.plan_id}) == 200 else true
```

This is genuinely hard to test manually. Apophis makes it declarative and automatic.

### 2. Property-Based Generation

Fast-check found edge cases we missed:
- Empty string `name` (schema allowed it, service rejected it)
- Invalid `billing_interval` values
- Missing required fields

### 3. Schema as Single Source of Truth

Once schemas are correct, contracts are free. The `x-ensures` array supplements rather than replaces schema validation.

### 4. Fast Feedback Loop

Contract tests run in ~1.5s for 4 routes. Much faster than spinning up a full test environment.

---

## Part 5: Feature Requests

### 1. Hypermedia Contract Support

Arbiter returns LDF (Linked Data Fragment) responses with `controls` and `actions`. We'd love to verify:

```
if status:200 then response_body(this).controls.self == request_url(this) else true
if status:200 then response_body(this).actions.create.method == "POST" else true
if status:200 then response_body(this).actions.update.target == "/billing/plans/{response_body(this).data.id}" else true
```

Currently we have to write these manually. Could Apophis infer hypermedia controls from route registration?

### 2. Conditional Schema Contracts

Instead of removing `const` from schemas, allow:

```json
{
  "response": {
    "200": {
      "properties": {
        "fragment_type": { "const": "Action", "x-apophis-conditional": "status:200" }
      }
    }
  }
}
```

This preserves schema expressiveness while generating correct contracts.

### 3. Middleware Contract Verification

Our middleware chain is critical. We'd like to verify:

```
if request_headers(this).authorization == null then status:401 else true
if request_headers(this).x-tenant-id == null then status:400 else true
```

Apophis already supports `request_headers` — making this a first-class feature (e.g., `x-requires`) would be powerful.

### 4. State Cleanup Hooks

After destructive tests (DELETE), we need to clean up:

```javascript
await app.apophis.contract({
  routes: ['DELETE /billing/plans/:id'],
  cleanup: async (state) => {
    // Remove created plans from database
    await db.plans.deleteMany({ id: { $in: state.createdPlans } });
  }
});
```

This would enable stateful testing without polluting the test environment.

### 5. Contract Coverage Report

After running tests, we'd like:
```
Contract Coverage:
  POST /billing/plans:
    - 201 response: ✓ tested (42 cases)
    - 400 response: ✓ tested (8 cases)
    - 503 response: ✗ not tested
    - Cross-op GET: ✓ tested (42 cases)
```

This helps identify gaps in contract coverage.

---

## Conclusion

Apophis is a powerful tool that fills a gap in API testing — behavioral contracts and chaos testing. The core concepts are solid, but the implementation needs hardening for production use:

**Must-fix:** Bugs #1 and #2 (scope registry, route filtering)
**Should-fix:** Bug #3 (configurable invariants), inference aggressiveness
**Nice-to-have:** Hypermedia support, middleware contracts, coverage reports

We're committed to using Apophis for Arbiter's contract testing and will contribute fixes upstream. The value of cross-operation verification alone justifies the investment.

---

**Contact:** Arbiter Engineering Team
**Repository:** https://github.com/anomalyco/apophis (we'll open issues for each bug)