fix(fires): show a 47.6-hour-old detection as 2d, not 48h

formatAge and formatAgeLabel picked the hour unit on the raw value and
rounded afterwards, so a detection between 47.5 and 48 hours old read
48h, while one exactly 48 hours old read 2d. Round to whole hours first,
then choose the unit.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

docs/CURRENT-STATE.md

@@ -2221,6 +2221,7 @@ accessible name remains "Don't show this again". Control behavior is unchanged.
 ## FIRMS source status
 
 The FIRMS CSV parser rejects impossible acquisition calendar dates before the proxy filters records to the trailing 24 hours, while retaining valid UTC acquisition times.
+FIRMS ages round to whole hours before choosing a unit, so a 47.6-hour age reads "2d", not "48h".
 The `get_active_fires` tool reports acquisition times as UTC ISO timestamps,
 including zero-padded hours and minutes; missing or invalid dates and times
 remain `null`, including impossible calendar dates from a custom source.

src/layers/firms/model.js

@@ -526,7 +526,8 @@ export function createModel({
     if (!Number.isFinite(deltaMs) || deltaMs < 0) return '';
     const hours = deltaMs / 3600000;
     if (hours < 1) return '<1h';
-    if (hours < 48) return `${Math.round(hours)}h`;
+    const wholeHours = Math.round(hours);
+    if (wholeHours < 48) return `${wholeHours}h`;
     return `${Math.round(hours / 24)}d`;
   }
 
@@ -561,8 +562,9 @@ export function createModel({
     if (!Number.isFinite(deltaMs) || deltaMs < 0) return '';
     const hours = deltaMs / 3600000;
     if (hours < 1) return t('<1h', { context: 'age' });
-    if (hours < 48)
-      return t('{count}h', { context: 'age', count: Math.round(hours) });
+    const wholeHours = Math.round(hours);
+    if (wholeHours < 48)
+      return t('{count}h', { context: 'age', count: wholeHours });
     return t('{count}d', { context: 'age', count: Math.round(hours / 24) });
   }
 

src/layers/firms/model.test.mjs

@@ -0,0 +1,24 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { getLocale, setLocale } from '../../i18n/index.js';
+import { createModel } from './model.js';
+
+const HOUR_MS = 3600000;
+
+test('a fire age that rounds to 48 hours reads in days, as 48 hours does', () => {
+  const previousLocale = getLocale();
+  const { formatAge, formatAgeLabel } = createModel({
+    services: { anchors: {} },
+  });
+  try {
+    setLocale('en');
+    assert.equal(formatAge(47.4 * HOUR_MS), '47h');
+    assert.equal(formatAge(47.6 * HOUR_MS), '2d');
+    assert.equal(formatAge(48 * HOUR_MS), '2d');
+    assert.equal(formatAgeLabel(47.4 * HOUR_MS), '47h');
+    assert.equal(formatAgeLabel(47.6 * HOUR_MS), formatAgeLabel(48 * HOUR_MS));
+    assert.equal(formatAgeLabel(48 * HOUR_MS), '2d');
+  } finally {
+    setLocale(previousLocale);
+  }
+});