bugfix: appointment hours now use the client timezone on UTC servers.

Logical API errors throw stable codes so users see translated messages instead of a generic bad request.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/lib/api/account.ts

@@ -1,4 +1,5 @@
 import { apiClient } from './client';
+import { getClientTimeZone } from '@/lib/i18n/clientTimeZone';
 
 export type WorkingHoursPayload = {
   autoRepeatWeekly: boolean;
@@ -42,7 +43,10 @@ export const accountApi = {
   upsertMyWorkingHours: async (
     payload: WorkingHoursPayload,
   ): Promise<{ success: boolean; message: string }> => {
-    const response = await apiClient.put('/auth/profile/working-hours', payload);
+    const response = await apiClient.put('/auth/profile/working-hours', {
+      ...payload,
+      timeZone: getClientTimeZone(),
+    });
     return response.data;
   },
 };

frontend/src/lib/api/appointments.ts

@@ -1,5 +1,6 @@
 import { apiClient } from './client';
 import type { AppointmentColumnProvider, AppointmentRecord } from '@/types/appointment';
+import { getClientTimeZone } from '@/lib/i18n/clientTimeZone';
 import { toDateInputValue } from '@/components/appointments/appointmentTime';
 
 export interface CreateAppointmentBody {
@@ -27,7 +28,10 @@ export const appointmentsApi = {
   },
 
   create: async (body: CreateAppointmentBody): Promise<{ success: boolean; data: AppointmentRecord }> => {
-    const response = await apiClient.post('/appointments', body);
+    const response = await apiClient.post('/appointments', {
+      ...body,
+      timeZone: getClientTimeZone(),
+    });
     return response.data;
   },
 
@@ -35,7 +39,10 @@ export const appointmentsApi = {
     id: string,
     body: UpdateAppointmentBody,
   ): Promise<{ success: boolean; data: AppointmentRecord }> => {
-    const response = await apiClient.patch(`/appointments/${id}`, body);
+    const response = await apiClient.patch(`/appointments/${id}`, {
+      ...body,
+      timeZone: getClientTimeZone(),
+    });
     return response.data;
   },
 

frontend/src/lib/api/staff.ts

@@ -1,4 +1,5 @@
 import { apiClient } from './client';
+import { getClientTimeZone } from '@/lib/i18n/clientTimeZone';
 
 export interface StaffMemberDto {
   id: string;
@@ -142,7 +143,10 @@ export const staffApi = {
       blocks: { dayOfWeek: number; startMinute: number; endMinute: number; sortOrder?: number }[];
     },
   ): Promise<{ success: boolean; message: string }> => {
-    const response = await apiClient.put(`/staff/members/${membershipId}/working-hours`, body);
+    const response = await apiClient.put(`/staff/members/${membershipId}/working-hours`, {
+      ...body,
+      timeZone: getClientTimeZone(),
+    });
     return response.data;
   },
 };

frontend/src/lib/i18n/clientTimeZone.ts

@@ -0,0 +1,8 @@
+/** Browser IANA zone (e.g. Asia/Tehran). Used so the UTC server can interpret wall-clock hours. */
+export function getClientTimeZone(): string {
+  try {
+    return Intl.DateTimeFormat().resolvedOptions().timeZone || 'UTC';
+  } catch {
+    return 'UTC';
+  }
+}