perf: bound runtime memory and storage usage

test/back/metrics.test.cjs

@@ -0,0 +1,34 @@
+const assert = require('node:assert/strict');
+const test = require('node:test');
+
+const {
+  MAX_METRIC_SAMPLES,
+  metricsService,
+} = require('../../back/services/metrics');
+
+test('metrics keep only the newest bounded samples', () => {
+  const sampleCount = MAX_METRIC_SAMPLES * 50;
+  for (let index = 0; index < sampleCount; index++) {
+    metricsService.record('http_request', index, {
+      path: `/health/${index}`,
+    });
+  }
+
+  const result = metricsService.getMetrics('http_request');
+  assert.equal(result.count, MAX_METRIC_SAMPLES);
+  assert.equal(result.metrics[0].value, sampleCount - MAX_METRIC_SAMPLES);
+  assert.equal(result.metrics.at(-1).value, sampleCount - 1);
+});
+
+test('empty metric queries return finite aggregates', () => {
+  const result = metricsService.getMetrics('missing_metric');
+  assert.deepEqual(
+    {
+      count: result.count,
+      average: result.average,
+      min: result.min,
+      max: result.max,
+    },
+    { count: 0, average: 0, min: 0, max: 0 },
+  );
+});