Changes Made

1. config/schema.sql — Added timezone_name VARCHAR(100) to user_preferences table + an ALTER TABLE migration at the bottom for existing DBs.
  2. core/tz.py — Rewrote with dual-path timezone support:
  - Request context: _get_request_tz() now checks X-Timezone-Name header (IANA) first, falls back to X-Timezone-Offset
  - Background jobs: New tz_for_user(user_uuid) and user_now_for(user_uuid) read stored timezone_name from prefs, fall back to numeric offset, then UTC
  - All existing function signatures (user_now(), user_today()) preserved for backward compat

  3. scheduler/daemon.py — Fixed 3 bugs:
  - _user_now_for() now delegates to tz.user_now_for() which uses IANA timezone names (DST-safe)
  - check_nagging() — replaced datetime.utcnow() with _user_now_for(user_uuid) so nags evaluate in user's timezone
  - poll_callback() — replaced single UTC midnight check with _check_per_user_midnight_schedules() that iterates users and creates daily schedules at their local midnight

  4. api/routes/preferences.py — Added "timezone_name" to allowed PUT fields.

  5. synculous-client/src/lib/api.ts — Added X-Timezone-Name header to every request + added timezone_name to preferences update type.

  6. synculous-client/src/app/dashboard/layout.tsx — Now syncs both timezone_offset and timezone_name (via Intl.DateTimeFormat().resolvedOptions().timeZone) on session start.

synculous-client/src/app/dashboard/layout.tsx

@@ -49,12 +49,13 @@ export default function DashboardLayout({
     }
   }, [isAuthenticated, isLoading, router]);
 
-  // Sync timezone offset to backend once per session
+  // Sync timezone to backend once per session
   useEffect(() => {
     if (isAuthenticated && !tzSynced.current) {
       tzSynced.current = true;
       const offset = new Date().getTimezoneOffset();
-      api.preferences.update({ timezone_offset: offset }).catch(() => {});
+      const tzName = Intl.DateTimeFormat().resolvedOptions().timeZone;
+      api.preferences.update({ timezone_offset: offset, timezone_name: tzName }).catch(() => {});
     }
   }, [isAuthenticated]);
 

synculous-client/src/lib/api.ts

@@ -21,6 +21,7 @@ async function request<T>(
   const headers: HeadersInit = {
     'Content-Type': 'application/json',
     'X-Timezone-Offset': String(new Date().getTimezoneOffset()),
+    'X-Timezone-Name': Intl.DateTimeFormat().resolvedOptions().timeZone,
     ...(token ? { Authorization: `Bearer ${token}` } : {}),
     ...options.headers,
   };
@@ -636,6 +637,7 @@ export const api = {
       show_launch_screen?: boolean;
       celebration_style?: string;
       timezone_offset?: number;
+      timezone_name?: string;
     }) => {
       return request<Record<string, unknown>>('/api/preferences', {
         method: 'PUT',