fix(server): person birthdate timezone bug (#31906)

fix(server): person birthdate timezone bug (#31901)

(cherry picked from commit 4b1b1f8c2a)

Co-authored-by: Jason Rasmussen <jason@rasm.me>

server/src/utils/date.spec.ts

@@ -1,7 +1,11 @@
-import { describe, expect, it } from 'vitest';
+import { afterEach, describe, expect, it, vi } from 'vitest';
 import { asDateString, asDateTimeString, isLeapDayObserved } from 'src/utils/date.js';
 
 describe('asDateString', () => {
+  afterEach(() => {
+    vi.unstubAllEnvs();
+  });
+
   it('should return null for null input', () => {
     expect(asDateString(null)).toBeNull();
   });
@@ -10,13 +14,17 @@ describe('asDateString', () => {
     expect(asDateString('2000-01-15')).toBe('2000-01-15');
   });
 
-  it('should return the local calendar date, not the UTC date', () => {
-    const date = new Date(2000, 0, 15); // 15 Jan 2000, local midnight
-    expect(asDateString(date)).toBe('2000-01-15');
-  });
+  // a `date` column is parsed as `new Date('YYYY-MM-DD')`, which is UTC midnight regardless of the server time zone
+  it.each(['UTC', 'America/Los_Angeles', 'America/New_York', 'Europe/Istanbul', 'Pacific/Kiritimati'])(
+    'should return the UTC calendar date of a date column when the server time zone is %s',
+    (timeZone) => {
+      vi.stubEnv('TZ', timeZone);
+      expect(asDateString(new Date('2000-01-15'))).toBe('2000-01-15');
+    },
+  );
 
   it('should correctly pad years with a leading 0', () => {
-    expect(asDateString(new Date('280-12-12'))).toBe('0280-12-12');
+    expect(asDateString(new Date('0280-12-12'))).toBe('0280-12-12');
   });
 });
 

server/src/validation.ts

@@ -171,7 +171,7 @@ export const isoDateToDate = z
     z.date(),
     {
       decode: (isoString) => new Date(isoString),
-      encode: (date) => DateTime.fromJSDate(date).toFormat('yyyy-MM-dd'),
+      encode: (date) => DateTime.fromJSDate(date, { zone: 'utc' }).toFormat('yyyy-MM-dd'),
     },
   )
   .meta({ example: '2024-01-01' });