fix: close REPL servers after each test to prevent Jest worker from hanging

Agent-Logs-Url: https://github.com/counterfact/api-simulator/sessions/6ff99a5b-2b06-4f18-b2a7-2b880122ff00

Author: Copilot

.changeset/fix-jest-open-handles.md

@@ -0,0 +1,5 @@
+---
+"counterfact": patch
+---
+
+Fix Jest worker process failing to exit gracefully by closing REPL servers after each test in the repl test suite.

test/repl/repl.test.ts

@@ -1,6 +1,6 @@
 import type { REPLServer } from "node:repl";
 
-import { jest } from "@jest/globals";
+import { afterEach, jest } from "@jest/globals";
 
 import { createCompleter, startRepl } from "../../src/repl/repl.js";
 import type { CompleterCallback } from "../../src/repl/repl.js";
@@ -101,9 +101,21 @@ function createHarness(scenarioRegistry?: ScenarioRegistry) {
     scenarioRegistry,
   );
 
+  openServers.push(harness.server);
+
   return { config, contextRegistry, harness, registry };
 }
 
+const openServers: REPLServer[] = [];
+
+afterEach(() => {
+  for (const server of openServers) {
+    server.close();
+  }
+
+  openServers.length = 0;
+});
+
 describe("REPL", () => {
   it("turns on the proxy globally", () => {
     const { config, harness } = createHarness();