PR1: Standardize emulator reset() contract + conformance test

CHANGELOG.md

@@ -0,0 +1,25 @@
+# Changelog
+
+All notable changes to Parlel are documented here. The format is based on
+[Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
+
+## [Unreleased]
+
+### Added
+
+- **Emulator contract conformance test** (`test/conformance.test.ts`). Asserts
+  across the whole catalog that every service has a valid manifest, a unique port,
+  a `src/server.js` exporting a `*Server` class, and that the class implements
+  `start()`, `stop()`, and `reset()`. Guards against convention drift as the
+  catalog grows. Includes a live boot → `/health` → `reset()` smoke test for a
+  representative sample of services.
+- **`reset()` standardized as part of the emulator contract.** Added `reset()` to
+  the services that were missing it (`cassandra`, `kafka`, `mysql`, `rabbitmq`,
+  `elasticsearch`, `supabase`), so every emulator can be returned to a clean state
+  for per-test isolation and by the forthcoming Parlel control plane.
+
+### Changed
+
+- `CONTRIBUTING.md` now documents the full emulator contract (`reset()` required,
+  all state initialized inside `reset()`), and the PR checklist references the
+  conformance test.

CONTRIBUTING.md

@@ -29,15 +29,32 @@ A service lives in `services/<slug>/` and needs three things:
 
 ### 2. `services/<slug>/src/server.js`
 
-Export a class named `<Something>Server` with a `constructor(port, options)`,
-a `start()` method (returns a promise once listening), and a `stop()` method.
+Export a class named `<Something>Server` implementing the **emulator contract**:
+
+- `constructor(port, options)` — store config; call `this.reset()`. No I/O here.
+- `start()` — returns a promise that resolves once listening.
+- `stop()` — returns a promise that resolves once closed.
+- `reset()` — clears **all** in-memory state back to empty. Idempotent, no I/O.
+
+`reset()` is required: it gives every test a clean slate and is what the Parlel
+control plane calls between test cases. Initialize all state inside `reset()` and
+call it from the constructor so the two never drift. The conformance test
+(`test/conformance.test.ts`) enforces this contract across the whole catalog.
 
 ```js
 import { createServer } from "node:http";
 
 export class MyServiceServer {
   constructor(port = 4900) {
     this.port = port;
+    this.server = null;
+    this.reset();
+  }
+
+  // Clears all in-memory state back to empty. Idempotent, no I/O.
+  reset() {
+    this.things = new Map();
+    this.counter = 0;
   }
 
   start() {
@@ -104,9 +121,11 @@ npm run probe                             # health-check
 ## PR checklist
 
 - [ ] `manifest.json`, `src/server.js`, `test/<slug>.test.ts` added.
+- [ ] `*Server` implements the contract: `constructor(port, options)`, `start()`,
+      `stop()`, `reset()` (all state initialized in `reset()`).
 - [ ] No new runtime dependencies (emulators stay pure Node).
 - [ ] Port doesn't clash with an existing service.
-- [ ] `npm test` passes.
+- [ ] `npm test` passes (including `test/conformance.test.ts`).
 - [ ] Real client library round-trips against the emulator.
 
 ## Code of conduct