refactor(fires): read both age formatters' unit from one helper

formatAge and formatAgeLabel repeated the validity guard, the <1h case,
the rounding and the 48-hour switch, which is why the rounding fix had to
land twice. Both now read { unit, count } from a private ageParts, so
they cannot pick different units again. Output is unchanged.

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

src/layers/firms/model.js

@@ -535,15 +535,26 @@ export function createModel({
     return `${isolate(latPart)} ${isolate(lonPart)}`;
   }
 
+  /**
+   * Millisecond delta → `{ unit: '<1h' | 'h' | 'd', count }`, or null for
+   * invalid input. Both age formatters read it, so they pick the same unit.
+   */
+
+  function ageParts(deltaMs) {
+    if (!Number.isFinite(deltaMs) || deltaMs < 0) return null;
+    const hours = deltaMs / 3600000;
+    if (hours < 1) return { unit: '<1h', count: 0 };
+    const wholeHours = Math.round(hours);
+    if (wholeHours < 48) return { unit: 'h', count: wholeHours };
+    return { unit: 'd', count: Math.round(hours / 24) };
+  }
+
   /** Millisecond delta → "<1h" / "Xh" / "Xd", or '' for invalid input. */
 
   function formatAge(deltaMs) {
-    if (!Number.isFinite(deltaMs) || deltaMs < 0) return '';
-    const hours = deltaMs / 3600000;
-    if (hours < 1) return '<1h';
-    const wholeHours = Math.round(hours);
-    if (wholeHours < 48) return `${wholeHours}h`;
-    return `${Math.round(hours / 24)}d`;
+    const age = ageParts(deltaMs);
+    if (!age) return '';
+    return age.unit === '<1h' ? '<1h' : `${age.count}${age.unit}`;
   }
 
   /** Millisecond delta → "<1m ago" / "Xm ago" / "Xh ago" (fresh-feed readout). */
@@ -574,13 +585,12 @@ export function createModel({
   /** formatAge for a card: "<1h", "24h", "3d" in the UI language ("24 ч"). */
 
   function formatAgeLabel(deltaMs) {
-    if (!Number.isFinite(deltaMs) || deltaMs < 0) return '';
-    const hours = deltaMs / 3600000;
-    if (hours < 1) return t('<1h', { context: 'age' });
-    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) });
+    const age = ageParts(deltaMs);
+    if (!age) return '';
+    if (age.unit === '<1h') return t('<1h', { context: 'age' });
+    return age.unit === 'h'
+      ? t('{count}h', { context: 'age', count: age.count })
+      : t('{count}d', { context: 'age', count: age.count });
   }
 
   /** Normalized 0..1 confidence → low/nominal/high display bucket. */

src/layers/firms/model.test.mjs

@@ -24,3 +24,22 @@ test('a fire age that rounds to 48 hours reads in days, as 48 hours does', () =>
     setLocale(previousLocale);
   }
 });
+
+test('both fire age formatters agree on invalid, sub-hour and multi-day ages', () => {
+  const previousLocale = getLocale();
+  const { formatAge, formatAgeLabel } = createModel({
+    services: { anchors: {} },
+  });
+  try {
+    setLocale('en');
+    for (const format of [formatAge, formatAgeLabel]) {
+      assert.equal(format(-1), '');
+      assert.equal(format(Number.NaN), '');
+      assert.equal(format(0.5 * HOUR_MS), '<1h');
+      assert.equal(format(1 * HOUR_MS), '1h');
+      assert.equal(format(72 * HOUR_MS), '3d');
+    }
+  } finally {
+    setLocale(previousLocale);
+  }
+});