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.

config/schema.sql

@@ -154,6 +154,7 @@ CREATE TABLE IF NOT EXISTS user_preferences (
     show_launch_screen BOOLEAN DEFAULT TRUE,
     celebration_style VARCHAR(50) DEFAULT 'standard',
     timezone_offset INTEGER DEFAULT 0,
+    timezone_name VARCHAR(100),
     created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
 );
 
@@ -293,3 +294,7 @@ CREATE TABLE IF NOT EXISTS snitch_log (
 
 CREATE INDEX IF NOT EXISTS idx_snitch_log_user_date ON snitch_log(user_uuid, DATE(sent_at));
 CREATE INDEX IF NOT EXISTS idx_snitch_contacts_user ON snitch_contacts(user_uuid, is_active);
+
+-- ── Migrations ──────────────────────────────────────────────
+-- Add IANA timezone name to user preferences (run once on existing DBs)
+ALTER TABLE user_preferences ADD COLUMN IF NOT EXISTS timezone_name VARCHAR(100);