Keep holidays/Hebrew-date overlays when changing year

src/components/LinearCalendar.tsx

@@ -491,6 +491,11 @@ export default function LinearCalendar({ events: initialEventsProp, startDate, e
         params.delete('start');
         params.delete('end');
         params.set('year', String(year));
+        // Rebuild `calendars` from component state (the source of truth) rather
+        // than trusting the URL, which may not have committed the most recent
+        // toggle yet — otherwise the holidays/Hebrew-date overlays get dropped
+        // on the first year change after enabling them.
+        applyCalendarsParam(params, { regularIds: visibleCalendarIds, showJewishCalendar, showHebrewDate });
         router.push(`/?${params.toString()}`);
     };
 
@@ -515,7 +520,8 @@ export default function LinearCalendar({ events: initialEventsProp, startDate, e
         params.delete('year');
         params.set('start', format(newStart, 'yyyy-MM'));
         params.set('end', format(newEnd, 'yyyy-MM'));
-
+        // Preserve the overlays/visible calendars from state (see changeYear).
+        applyCalendarsParam(params, { regularIds: visibleCalendarIds, showJewishCalendar, showHebrewDate });
         router.push(`/?${params.toString()}`);
     };
 

src/lib/calendar-params.test.ts

@@ -91,4 +91,21 @@ describe('applyCalendarsParam', () => {
         expect(ids).toContain('work');
         expect(ids).toContain(JEWISH_CALENDAR_ID);
     });
+
+    // Regression: changing the year must keep the overlays even when the URL
+    // hasn't committed the most recent toggle yet — by rebuilding `calendars`
+    // from component state, not from the (stale) URL.
+    it('year navigation rebuilds overlays from state over a stale URL', () => {
+        const params = new URLSearchParams('calendars=primary&year=2026'); // URL missing overlays
+        params.set('year', '2027');
+        applyCalendarsParam(params, {
+            regularIds: ['primary'],
+            showJewishCalendar: true, // state says they ARE on
+            showHebrewDate: true,
+        });
+        const ids = params.get('calendars')!.split(',');
+        expect(ids).toContain(JEWISH_CALENDAR_ID);
+        expect(ids).toContain(HEBREW_DATE_ID);
+        expect(params.get('year')).toBe('2027');
+    });
 });