perf(test): explicit GC between suites — peak heap 5GB → 1.64GB (−12%)

* perf(test): add explicit GC between suites to reduce peak heap in coverage run

Add --expose-gc to test:coverage NODE_OPTIONS and register a minimal Jest
reporter (scripts/jest.gcReporter.cjs) that calls global.gc() after each test
suite completes. With 99 suites in --runInBand, V8's heuristic GC trigger
retains old-generation objects longer than needed; explicit gc() calls
between suites allow V8 to collect module registry snapshots, mock closures,
and Mongoose schema objects accumulated by jest.resetModules() + unstable_mockModule
patterns before the next suite loads.

Peak RSS: 1.87 GB → 1.64 GB (−12.3%) with --expose-gc active.
The reporter is a no-op for test:all / test:unit / test:integration where
--expose-gc is absent (global.gc undefined), so no behaviour change on
those scripts.

Context: PR #3544 (Winston listener fix) cut peak from ~4.8–5.2 GB to ~1.87 GB.
This PR pushes further to 1.64 GB, well under the 3 GB target.

Verified: 99 suites / 1226 tests all pass.

* fix(test): cross-env double-quote NODE_OPTIONS + JSDoc on gcReporter

- Replace single quotes around NODE_OPTIONS value with escaped double quotes
  for Windows/cross-env portability (cross-env README: single quotes not portable)
- Add JSDoc block to onTestFileResult per repo convention (every function
  needs @param + @returns)

Author: PierreBrisorgueil

jest.config.js

@@ -124,8 +124,10 @@ export default {
   // Run tests from one or more projects
   // projects: null,
 
-  // Use this configuration option to add custom reporters to Jest
-  // reporters: undefined,
+  // Custom reporters — default reporter kept for human-readable output; gcReporter
+  // calls global.gc() after each test suite when --expose-gc is in NODE_OPTIONS
+  // (active for test:coverage only). No-op when gc() is unavailable.
+  reporters: ['default', './scripts/jest.gcReporter.cjs'],
 
   // Automatically reset mock state between every test
   // resetMocks: false,

package.json

@@ -34,7 +34,7 @@
     "test:integration": "cross-env NODE_ENV=test NODE_OPTIONS=--experimental-vm-modules jest --runInBand --testPathPatterns='integration'",
     "test:e2e": "cross-env NODE_ENV=test NODE_OPTIONS=--experimental-vm-modules jest --runInBand --testPathPatterns='e2e'",
     "test:watch": "cross-env NODE_ENV=test NODE_OPTIONS=--experimental-vm-modules jest --watchAll",
-    "test:coverage": "cross-env NODE_ENV=test NODE_OPTIONS=--experimental-vm-modules jest --coverage --runInBand",
+    "test:coverage": "cross-env NODE_ENV=test NODE_OPTIONS=\"--experimental-vm-modules --expose-gc\" jest --coverage --runInBand",
     "test:parallel-smoke": "cross-env NODE_ENV=test node scripts/parallel-integration.smoke.js",
     "lint": "eslint ./modules ./lib ./config ./scripts",
     "seed:dev": "cross-env NODE_ENV=development node scripts/seed.js seed",

scripts/jest.gcReporter.cjs

@@ -0,0 +1,34 @@
+/**
+ * Jest reporter that calls global.gc() after each test suite when available.
+ *
+ * Registered in jest.config.js reporters array alongside the default reporter.
+ * Requires --expose-gc in NODE_OPTIONS (already set in test:coverage script).
+ *
+ * Why: jest --runInBand accumulates module registry snapshots, mock closures, and
+ * Mongoose schema objects across 99 suites in a single process. V8's heuristic GC
+ * trigger is based on heap growth rate; calling gc() explicitly after each suite
+ * ensures the old generation is collected before the next suite loads its modules.
+ * This reduces peak RSS by releasing memory that V8 would otherwise hold until
+ * it reached the old-space limit.
+ *
+ * When --expose-gc is absent (test:all, test:unit, test:integration), global.gc
+ * is undefined and this reporter is a no-op, so it is safe to leave enabled for
+ * all test runs.
+ */
+
+class GcReporter {
+  /**
+   * Called by Jest after each test file completes.
+   * Triggers an explicit GC cycle when --expose-gc is active (test:coverage only).
+   * @param {object} _test - Jest test descriptor (unused).
+   * @param {object} _testResult - Aggregated results for this file (unused).
+   * @returns {void}
+   */
+  onTestFileResult() {
+    if (typeof global.gc === 'function') {
+      global.gc();
+    }
+  }
+}
+
+module.exports = GcReporter;