fix(voice): leave out an unreported altitude instead of saying 0 feet

select_nearest_aircraft passes altitudeM: null for an airborne contact
without a barometric altitude (military rows from adsb.lol can lack
alt_baro). The speech builder coerced it with Number(), and Number(null)
is 0, so the reply said "..., 0 feet." and the voice card showed
"Altitude 0 feet". Read the altitude only when it is a finite number,
so an unknown one is left out as the builder already intends.

docs/CURRENT-STATE.md

@@ -5115,6 +5115,8 @@ and unreachable upstream (502/504) separately from road geometry.
   cannot race the nearest-aircraft query ahead of layer enablement. A healthy fallback feed is
   queried normally and its source is returned with the selection; fallback with
   no airborne records remains an honest no-data result, not an enable failure.
+  The spoken reply and the card leave out an altitude the feed did not report
+  rather than reading it as 0 feet.
 - Voice treats the parent Context panel and Contacts as separate intents. An
   explicit request to open Context expands only `global-context-panel`; it does
   not choose a mode. An explicit request to open Contacts expands that parent

src/voice/speech.js

@@ -74,9 +74,9 @@ function listPhrase(items) {
 }
 
 function feetRounded(meters) {
-  const value = Number(meters);
+  // A missing altitude is unknown, not sea level: Number(null) is 0.
-  return Number.isFinite(value)
+  return Number.isFinite(meters)
-    ? Math.round((value * 3.28084) / 100) * 100
+    ? Math.round((meters * 3.28084) / 100) * 100
     : null;
 }
 

src/voice/speech.test.mjs

@@ -217,6 +217,20 @@ test('nearest-aircraft results name the aircraft, distance and altitude briefly'
   assert.equal(stale.say, 'Selected AAL1, 3.3 km from Austin, stale.');
 });
 
+test('nearest-aircraft results leave out an altitude the feed did not report', () => {
+  // gevActions sends `altitudeM: null` for an airborne military contact
+  // without a barometric altitude; that is unknown, not sea level.
+  const unknown = envelope('select_nearest_aircraft', {
+    ok: true,
+    location: 'Ramstein',
+    layerId: 'military',
+    feed: { state: 'nominal' },
+    aircraft: { callsign: 'RCH123', altitudeM: null, distanceKm: 8.2 },
+  });
+  assert.equal(unknown.say, 'Selected RCH123, 8.2 km from Ramstein.');
+  assert.deepEqual(unknown.display.lines, ['8.2\u00a0km from Ramstein']);
+});
+
 test('frame_overhead keeps the essential scope audible and lists referents', () => {
   const framed = envelope('frame_overhead', {
     ok: true,