refactor: stabilize cumulative mileage metrics

src/server/routes/analytics/index.test.ts

@@ -7,7 +7,7 @@ test('returns the published mileage metric contract', async () => {
   const payload = await response.json();
 
   assert.equal(response.status, 200);
-  assert.equal(payload.catalogVersion, 5);
+  assert.equal(payload.catalogVersion, 6);
   assert.deepEqual(payload.domains, ['mileage']);
   assert.ok(payload.metrics.some((metric: { id: string }) => metric.id === 'mileage.assessment_completion_rate'));
 });
@@ -27,7 +27,7 @@ test('returns the published electric metric contract', async () => {
   const payload = await response.json();
 
   assert.equal(response.status, 200);
-  assert.equal(payload.catalogVersion, 5);
+  assert.equal(payload.catalogVersion, 6);
   assert.deepEqual(payload.domains, ['electric']);
   assert.ok(payload.metrics.some((metric: { id: string }) => metric.id === 'electric.charge_total_fee'));
   assert.ok(payload.metrics.some((metric: { id: string }) => metric.id === 'electric.blended_cost_intensity'));
@@ -39,7 +39,7 @@ test('returns the published ETC metric contract', async () => {
   const payload = await response.json();
 
   assert.equal(response.status, 200);
-  assert.equal(payload.catalogVersion, 5);
+  assert.equal(payload.catalogVersion, 6);
   assert.deepEqual(payload.domains, ['etc']);
   assert.ok(payload.metrics.some((metric: { id: string }) => metric.id === 'etc.total_amount'));
   assert.ok(payload.metrics.some((metric: { id: string }) => metric.id === 'etc.bill_receivable'));

src/server/routes/mileage/monitoring.ts

@@ -17,6 +17,7 @@ import {
   getManualMonitoringSnapshot,
   storeManualMonitoringSnapshot,
 } from './manual-snapshot.js';
+import { sumMileageKm } from './precision.js';
 
 const app = new Hono();
 
@@ -245,9 +246,9 @@ app.get('/', async (c) => {
 
   const stats = {
     totalToday: Math.round(filtered.reduce((sum, v) => sum + v.dailyKm, 0)),
-    totalAll: filtered.reduce((sum, v) => sum + (v.totalKm || 0), 0),
+    totalAll: sumMileageKm(filtered.map(v => v.totalKm || 0)),
     vehicleCount: filtered.length,
-    yesterdayTotal: filtered.reduce((sum, v) => sum + v.yesterdayKm, 0),
+    yesterdayTotal: sumMileageKm(filtered.map(v => v.yesterdayKm)),
   };
 
   const sorted = [...filtered].sort((a, b) => {

src/server/routes/mileage/precision.test.ts

@@ -0,0 +1,13 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { roundMileageKm, sumMileageKm } from './precision.js';
+
+test('removes binary floating point tails at the published precision', () => {
+  assert.equal(sumMileageKm([0.1, 0.2]), 0.3);
+  assert.equal(roundMileageKm(44_488_200.300000004), 44_488_200.3);
+});
+
+test('rounds after aggregation and ignores invalid values', () => {
+  assert.equal(sumMileageKm([0.04, 0.04]), 0.1);
+  assert.equal(sumMileageKm([1, Number.NaN, Number.POSITIVE_INFINITY]), 1);
+});

src/server/routes/mileage/precision.ts

@@ -0,0 +1,13 @@
+export function roundMileageKm(value: number, decimals = 1): number {
+  if (!Number.isFinite(value)) return 0;
+  const scale = 10 ** decimals;
+  return Math.round((value + Number.EPSILON) * scale) / scale;
+}
+
+export function sumMileageKm(values: Iterable<number>, decimals = 1): number {
+  let total = 0;
+  for (const value of values) {
+    if (Number.isFinite(value)) total += value;
+  }
+  return roundMileageKm(total, decimals);
+}