fix(cockpit): read a rounded-north destination heading as 000

359.6 degrees was shown as 360 degrees on the destination bearing while the compass tape uses 000.

src/cockpitMath.js

@@ -6,6 +6,15 @@ export function normalizeHeading(value) {
   return ((value % 360) + 360) % 360;
 }
 
+/**
+ * Three-digit heading readout, 000–359.
+ * Rounding 359.5° and above lands on north (000), not 360.
+ */
+export function formatHeadingReadout(degrees) {
+  if (!Number.isFinite(degrees)) return '---';
+  return String(Math.round(normalizeHeading(degrees)) % 360).padStart(3, '0');
+}
+
 /** Advance a displayed heading along the shortest arc without exceeding a slew rate. */
 export function slewHeading(current, target, maxStepDeg) {
   const from = normalizeHeading(current);

src/cockpitMath.test.mjs

@@ -15,6 +15,7 @@ import {
   formatCockpitContextScope,
   formatCockpitEmergency,
   formatCompassDivision,
+  formatHeadingReadout,
   formatSpeedRulerTick,
   normalizeHeading,
   relativeBearing,
@@ -155,6 +156,14 @@ test('compass labels use cardinals where exact and degrees elsewhere', () => {
   assert.equal(formatCompassDivision(30), '030');
 });
 
+test('a heading that rounds to north reads 000, not 360', () => {
+  assert.equal(formatHeadingReadout(359.6), '000');
+  assert.equal(formatHeadingReadout(359.4), '359');
+  assert.equal(formatHeadingReadout(0), '000');
+  assert.equal(formatHeadingReadout(10.2), '010');
+  assert.equal(formatHeadingReadout(Number.NaN), '---');
+});
+
 test('great-circle bearing resolves cardinal directions', () => {
   assert.ok(Math.abs(bearingBetweenCoordinates(0, 0, 1, 0) - 0) < 0.001);
   assert.ok(Math.abs(bearingBetweenCoordinates(0, 0, 0, 1) - 90) < 0.001);

src/ui/cockpitInstruments.js

@@ -14,6 +14,7 @@ import {
   formatAltitudeRulerTick,
   formatCompassDivision,
   formatCockpitEmergency,
+  formatHeadingReadout,
   formatSpeedRulerTick,
   normalizeHeading,
   relativeBearing,
@@ -238,7 +239,7 @@ export function updateRoute(info) {
   }
   if (this.routeDirectionLabel) {
     this.routeDirectionLabel.textContent = t('DEST {bearing}', {
-      bearing: `${String(Math.round(destinationBearing)).padStart(3, '0')}°`,
+      bearing: `${formatHeadingReadout(destinationBearing)}°`,
     });
   }
 }