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.

api/routes/preferences.py

@@ -58,7 +58,7 @@ def register(app):
         if not data:
             return flask.jsonify({"error": "missing body"}), 400
 
-        allowed = ["sound_enabled", "haptic_enabled", "show_launch_screen", "celebration_style", "timezone_offset"]
+        allowed = ["sound_enabled", "haptic_enabled", "show_launch_screen", "celebration_style", "timezone_offset", "timezone_name"]
         updates = {k: v for k, v in data.items() if k in allowed}
         if not updates:
             return flask.jsonify({"error": "no valid fields"}), 400

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);

core/tz.py

@@ -1,12 +1,36 @@
 """
 core/tz.py - Timezone-aware date/time helpers
 
-The frontend sends X-Timezone-Offset (minutes from UTC, same sign as
-JavaScript's getTimezoneOffset — positive means behind UTC).
-These helpers convert server UTC to the user's local date/time.
+The frontend sends:
+  X-Timezone-Name   – IANA timezone (e.g. "America/Chicago"), preferred
+  X-Timezone-Offset – minutes from UTC (JS getTimezoneOffset sign), fallback
+
+For background tasks (no request context) the scheduler reads the stored
+timezone_name / timezone_offset from user_preferences.
 """
 
 from datetime import datetime, date, timezone, timedelta
+from zoneinfo import ZoneInfo
+
+import core.postgres as postgres
+
+# ── Request-context helpers (used by Flask route handlers) ────────────
+
+def _get_request_tz():
+    """Return a tzinfo from the current Flask request headers.
+    Prefers X-Timezone-Name (IANA), falls back to X-Timezone-Offset."""
+    try:
+        import flask
+        name = flask.request.headers.get("X-Timezone-Name")
+        if name:
+            try:
+                return ZoneInfo(name)
+            except (KeyError, Exception):
+                pass
+        offset = int(flask.request.headers.get("X-Timezone-Offset", 0))
+        return timezone(timedelta(minutes=-offset))
+    except (ValueError, TypeError, RuntimeError):
+        return timezone.utc
 
 
 def _get_offset_minutes():
@@ -16,7 +40,6 @@ def _get_offset_minutes():
         import flask
         return int(flask.request.headers.get("X-Timezone-Offset", 0))
     except (ValueError, TypeError, RuntimeError):
-        # RuntimeError: outside of request context
         return 0
 
 
@@ -26,14 +49,45 @@ def _offset_to_tz(offset_minutes):
 
 
 def user_now(offset_minutes=None):
-    """Current datetime in the user's timezone.
-    If offset_minutes is provided, uses that instead of the request header."""
-    if offset_minutes is None:
-        offset_minutes = _get_offset_minutes()
-    tz = _offset_to_tz(offset_minutes)
+    """Current datetime in the user's timezone (request-context).
+    If offset_minutes is provided, uses that directly.
+    Otherwise reads request headers (prefers IANA name over offset)."""
+    if offset_minutes is not None:
+        tz = _offset_to_tz(offset_minutes)
+    else:
+        tz = _get_request_tz()
     return datetime.now(tz)
 
 
 def user_today(offset_minutes=None):
     """Current date in the user's timezone."""
     return user_now(offset_minutes).date()
+
+
+# ── Stored-preference helpers (used by scheduler / background jobs) ───
+
+def tz_for_user(user_uuid):
+    """Return a tzinfo for *user_uuid* from stored preferences.
+    Priority: timezone_name (IANA) > timezone_offset (minutes) > UTC."""
+    prefs = postgres.select_one("user_preferences", {"user_uuid": user_uuid})
+    if prefs:
+        name = prefs.get("timezone_name")
+        if name:
+            try:
+                return ZoneInfo(name)
+            except (KeyError, Exception):
+                pass
+        offset = prefs.get("timezone_offset")
+        if offset is not None:
+            return timezone(timedelta(minutes=-offset))
+    return timezone.utc
+
+
+def user_now_for(user_uuid):
+    """Current datetime in a user's timezone using their stored preferences."""
+    return datetime.now(tz_for_user(user_uuid))
+
+
+def user_today_for(user_uuid):
+    """Current date in a user's timezone using their stored preferences."""
+    return user_now_for(user_uuid).date()

scheduler/daemon.py

@@ -13,6 +13,7 @@ import core.postgres as postgres
 import core.notifications as notifications
 import core.adaptive_meds as adaptive_meds
 import core.snitch as snitch
+import core.tz as tz
 
 logging.basicConfig(level=logging.INFO)
 logger = logging.getLogger(__name__)
@@ -21,14 +22,8 @@ POLL_INTERVAL = int(os.environ.get("POLL_INTERVAL", 60))
 
 
 def _user_now_for(user_uuid):
-    """Get current datetime in a user's timezone using their stored offset."""
-    prefs = postgres.select_one("user_preferences", {"user_uuid": user_uuid})
-    offset_minutes = 0
-    if prefs and prefs.get("timezone_offset") is not None:
-        offset_minutes = prefs["timezone_offset"]
-    # JS getTimezoneOffset: positive = behind UTC, so negate
-    tz_obj = timezone(timedelta(minutes=-offset_minutes))
-    return datetime.now(tz_obj)
+    """Get current datetime in a user's timezone using their stored preferences."""
+    return tz.user_now_for(user_uuid)
 
 
 def check_medication_reminders():
@@ -158,7 +153,8 @@ def check_refills():
 
 
 def create_daily_adaptive_schedules():
-    """Create today's medication schedules with adaptive timing."""
+    """Create today's medication schedules with adaptive timing.
+    Called per-user when it's midnight in their timezone."""
     try:
         from datetime import date as date_type
 
@@ -312,7 +308,7 @@ def check_nagging():
                 logger.debug(f"Nagging disabled for user {user_uuid}")
                 continue
 
-            now = datetime.utcnow()
+            now = _user_now_for(user_uuid)
             today = now.date()
 
             # Get today's schedules
@@ -428,18 +424,55 @@ def check_nagging():
         logger.error(f"Error checking nags: {e}")
 
 
-def poll_callback():
-    """Called every POLL_INTERVAL seconds."""
-    # Create daily schedules at midnight
-    now = datetime.utcnow()
-    if now.hour == 0 and now.minute < POLL_INTERVAL / 60:
+def _get_distinct_user_uuids():
+    """Return a set of user UUIDs that have active medications or routines."""
+    uuids = set()
+    try:
+        meds = postgres.select("medications", where={"active": True})
+        for m in meds:
+            uid = m.get("user_uuid")
+            if uid:
+                uuids.add(uid)
+    except Exception:
+        pass
+    try:
+        routines = postgres.select("routines")
+        for r in routines:
+            uid = r.get("user_uuid")
+            if uid:
+                uuids.add(uid)
+    except Exception:
+        pass
+    return uuids
+
+
+def _check_per_user_midnight_schedules():
+    """Create daily adaptive schedules for each user when it's midnight in
+    their timezone (within the poll window)."""
+    for user_uuid in _get_distinct_user_uuids():
         try:
-            create_daily_adaptive_schedules()
+            now = _user_now_for(user_uuid)
+            if now.hour == 0 and now.minute < POLL_INTERVAL / 60:
+                user_meds = postgres.select(
+                    "medications", where={"user_uuid": user_uuid, "active": True}
+                )
+                for med in user_meds:
+                    times = med.get("times", [])
+                    if times:
+                        adaptive_meds.create_daily_schedule(
+                            user_uuid, med["id"], times
+                        )
         except Exception as e:
             logger.warning(
-                f"Could not create adaptive schedules (tables may not exist): {e}"
+                f"Could not create adaptive schedules for user {user_uuid}: {e}"
             )
 
+
+def poll_callback():
+    """Called every POLL_INTERVAL seconds."""
+    # Create daily schedules per-user at their local midnight
+    _check_per_user_midnight_schedules()
+
     # Check reminders - use both original and adaptive checks
     logger.info("Checking medication reminders")
     check_medication_reminders()

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',