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

[Copilot]

Summary

Each test in test/repl/repl.test.ts called startRepl() → repl.start(), creating a Node.js REPLServer that holds process.stdin open. Nothing ever closed them, so Jest workers couldn't exit, producing the "worker process has failed to exit gracefully" error.

Changes:

• test/repl/repl.test.ts: track every REPLServer created by createHarness() in a module-level array; drain and close all of them in afterEach

const openServers: REPLServer[] = [];

afterEach(() => {
  for (const server of openServers) {
    server.close();
  }
  openServers.length = 0;
});

function createHarness(scenarioRegistry?: ScenarioRegistry) {
  // ...
  openServers.push(harness.server);
  return { config, contextRegistry, harness, registry };
}

Original Prompt

Jest is reporting open handles. Fix the issue so Jest can exit gracefully.

Manual acceptance tests

• yarn test completes without "A worker process has failed to exit gracefully" in the output
• All 47 test suites pass after the change
• Running the repl test suite in isolation (yarn node --experimental-vm-modules ./node_modules/jest-cli/bin/jest --testPathPatterns=repl.test --coverageThreshold='{}') finishes in under 5 seconds instead of hanging

Tasks

• Confirmed repl.test.ts hangs indefinitely when run in isolation (timed out after 20 s)
• Added openServers tracking array and afterEach cleanup to test/repl/repl.test.ts
• Modified createHarness to register each new server for cleanup
• Verified repl test now completes in ~0.6 s; full suite (47 suites, 573 tests) passes clean