feat: implement admin panel functionality in Mini App

- Added new API endpoints for admin features: `GET /api/admin/me`, `GET /api/admin/users`, and `PATCH /api/admin/duties/:id` to manage user duties. - Introduced `UserForAdmin` and `AdminDutyReassignBody` schemas for handling admin-related data. - Updated documentation to include Mini App design guidelines and admin panel functionalities. - Enhanced tests for admin API to ensure proper access control and functionality. - Improved error handling and localization for admin actions.
2026-03-06 09:57:26 +03:00
parent 68b1884b73
commit c390a4dd6e
28 changed files with 2045 additions and 15 deletions
--- a/.cursor/rules/frontend.mdc
+++ b/.cursor/rules/frontend.mdc
@@ -50,4 +50,15 @@ The Mini App lives in `webapp-next/`. It is built as a static export and served
 - **Run:** `cd webapp-next && npm test` (or `npm run test`). Build: `npm run build`.
 - **Coverage:** Unit tests for lib (api, date-utils, calendar-data, i18n, etc.) and component tests for calendar, duty list, day detail, current duty, states.

+## Design guideline
+
+When adding or changing UI in the Mini App, **follow the [Mini App design guideline](../../docs/miniapp-design.md)**:
+
+- Use only design tokens from `globals.css` and Tailwind/shadcn aliases (no hardcoded colours).
+- Page wrappers: `content-safe`, `max-w-[var(--max-width-app)]`, viewport height; respect safe area for sheets/modals.
+- Reuse component patterns (buttons, cards, calendar grid, timeline list) and left-stripe semantics (`border-l-duty`, `border-l-today`, etc.).
+- Add ARIA labels and roles for interactive elements and grids; respect `prefers-reduced-motion` and `data-perf="low"` for animations.
+
+Use the checklist in the design doc when introducing new screens or components.
+
 Consider these rules when changing the Mini App or adding frontend features.
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -24,6 +24,7 @@ Duty Teller is a Telegram bot plus Mini App for team duty shift calendar and gro
 | Duty-schedule parser | `duty_teller/importers/` |
 | Config (env vars) | `duty_teller/config.py` |
 | Miniapp frontend | `webapp-next/` (Next.js, Tailwind, shadcn/ui; static export in `webapp-next/out/`) |
+| Admin panel (Mini App) | `webapp-next/src/app/admin/page.tsx`; API: `GET /api/admin/me`, `GET /api/admin/users`, `PATCH /api/admin/duties/:id` |
 | Migrations | `alembic/` (config in `pyproject.toml` under `[tool.alembic]`) |

 ## Running and testing
@@ -35,6 +36,7 @@ Duty Teller is a Telegram bot plus Mini App for team duty shift calendar and gro
 ## Documentation

 - User and architecture docs: [docs/](docs/), [docs/architecture.md](docs/architecture.md).
+- [Mini App design guideline](docs/miniapp-design.md) — Theme, layout, safe areas, component patterns, accessibility for webapp-next.
 - Configuration reference: [docs/configuration.md](docs/configuration.md).
 - Build docs: `pip install -e ".[docs]"`, then `mkdocs build` / `mkdocs serve`.

@@ -48,4 +50,5 @@ Docstrings and code comments must be in English (Google-style docstrings). UI st
 - **Config:** Environment variables (e.g. `.env`); no hardcoded secrets.
 - **Database:** One logical transaction per `session_scope` — a single `commit` at the end of the business operation (e.g. in `run_import`). Repository helpers used inside such a flow (e.g. `get_or_create_user_by_full_name`) accept `commit=False` and let the caller commit once.
 - **Error handling:** Do not send `str(exception)` from parsers or DB to the user. Use generic i18n keys (e.g. `import.parse_error_generic`, `import.import_error_generic`) and log the full exception server-side.
+- **Mini App (webapp-next):** When adding or changing UI in `webapp-next/`, follow the [Mini App design guideline](docs/miniapp-design.md): use only design tokens and Tailwind aliases from it, apply layout/safe-area/accessibility rules, and use the checklist for new screens or components.
 - **Cursor:** The project does not version `.cursor/`. You can mirror this file in `.cursor/rules/` locally; [AGENTS.md](AGENTS.md) is the single versioned reference for AI and maintainers.
--- a/docs/architecture.md
+++ b/docs/architecture.md
@@ -18,6 +18,9 @@ High-level architecture of Duty Teller: components, data flow, and package relat
 - **Miniapp → API**  
  Browser opens `/app`; frontend calls `GET /api/duties` and `GET /api/calendar-events` with date range. FastAPI dependencies: DB session, Telegram initData validation (`require_miniapp_username`), date validation. Data is read via `duty_teller.db.repository`.

+- **Admin panel (Mini App)**  
+  Admins see an "Admin" link on the calendar (when `GET /api/admin/me` returns `is_admin: true`). The admin page at `/app/admin` lists duties for the current month and allows reassigning a duty to another user. It uses `GET /api/admin/users` (admin-only) for the user dropdown and `PATCH /api/admin/duties/:id` with `{ user_id }` to reassign. All admin endpoints require valid initData; `/users` and PATCH `/duties` additionally require the user to have the admin role (`require_admin_telegram_id`). PATCH error messages (e.g. duty not found, user not found) use the request `Accept-Language` header for i18n. The reassign dropdown shows only users with role `user` or `admin` (role_id 1 or 2 per migration 007).
+
 - **Import**  
  Admin sends JSON file via `/import_duty_schedule`. Handler reads file → `duty_teller.importers.duty_schedule.parse_duty_schedule()` → `DutyScheduleResult` → `duty_teller.services.import_service.run_import()` → repository (`get_or_create_user_by_full_name`, `delete_duties_in_range`, `insert_duty`).

--- a/docs/index.md
+++ b/docs/index.md
@@ -6,6 +6,7 @@ Telegram bot for team duty shift calendar and group reminder. The bot and web UI

 - [Configuration](configuration.md) — Environment variables (types, defaults, examples).
 - [Architecture](architecture.md) — Components, data flow, package relationships.
+- [Mini App design](miniapp-design.md) — Design guideline for the Telegram Mini App (webapp-next): theme, layout, components, accessibility.
 - [Import format](import-format.md) — Duty-schedule JSON format and example.
 - [Runbook](runbook.md) — Running the app, logs, common errors, DB and migrations.
 - [API Reference](api-reference.md) — Generated from code (api, db, services, handlers, importers, config).
--- a/docs/miniapp-design.md
+++ b/docs/miniapp-design.md
@@ -0,0 +1,217 @@
+# Mini App Design Guideline
+
+This document defines the design rules for the Duty Teller Mini App (Next.js frontend in `webapp-next/`). It aligns with [Telegram’s official Mini App design guidelines](https://core.telegram.org/bots/webapps#designing-mini-apps) (Color Schemes and Design Guidelines) and codifies the current implementation (calendar, duty list, admin) as the reference for new screens and components.
+
+---
+
+## 1. Telegram design principles
+
+Telegram’s guidelines state:
+
+- **Mobile-first:** All elements must be responsive and designed for mobile first.
+- **Consistency:** Interactive elements should match the style, behaviour, and intent of existing Telegram UI components.
+- **Performance:** Animations should be smooth, ideally 60fps.
+- **Accessibility:** Inputs and images must have labels.
+- **Theme:** The app must use the dynamic theme-based colors provided by the API (Day/Night and custom themes).
+- **Safe areas:** The interface must respect the **safe area** and **content safe area** so content does not overlap system or Telegram UI, especially in fullscreen.
+- **Android:** On Android, use the extra User-Agent data (e.g. performance class) and reduce animations and effects on low-performance devices for smooth operation.
+
+**Color schemes:** Mini Apps receive the user’s current **theme** in real time. Use the `ThemeParams` object and the CSS variables Telegram exposes (e.g. `--tg-theme-bg-color`, `--tg-theme-text-color`) so the UI adapts when the user switches Day/Night or custom themes.
+
+---
+
+## 2. Theme and colors
+
+### 2.1 Sources
+
+Theme is resolved in this order:
+
+1. Hash parameters: `tgWebAppColorScheme`, `tgWebAppThemeParams` (parsed in the inline script in `webapp-next/src/app/layout.tsx`).
+2. At runtime: `Telegram.WebApp.colorScheme` and `Telegram.WebApp.themeParams` via `use-telegram-theme.ts` and `TelegramProvider`.
+
+The inline script in the layout maps all Telegram theme keys to `--tg-theme-*` CSS variables on the document root. The hook sets `data-theme` (`light` / `dark`) and applies Mini App background/header colors.
+
+### 2.2 Mapping (ThemeParams → app tokens)
+
+In `webapp-next/src/app/globals.css`, `:root` and `[data-theme="light"]` / `[data-theme="dark"]` map Telegram’s ThemeParams to internal design tokens:
+
+| Telegram ThemeParam (CSS var)        | App token / usage |
+|--------------------------------------|-------------------|
+| `--tg-theme-bg-color`                | `--bg` (background) |
+| `--tg-theme-secondary-bg-color`      | `--surface` (cards, panels) |
+| `--tg-theme-text-color`              | `--text` (primary text) |
+| `--tg-theme-hint-color`, `--tg-theme-subtitle-text-color` | `--muted` (secondary text) |
+| `--tg-theme-link-color`              | `--accent` (links, secondary actions) |
+| `--tg-theme-header-bg-color`          | `--header-bg` |
+| `--tg-theme-section-bg-color`        | `--card` (sections) |
+| `--tg-theme-section-header-text-color` | `--section-header` |
+| `--tg-theme-section-separator-color` | `--border` |
+| `--tg-theme-button-color`            | `--primary` |
+| `--tg-theme-button-text-color`       | `--primary-foreground` |
+| `--tg-theme-destructive-text-color` | `--error` |
+| `--tg-theme-accent-text-color`      | `--accent-text` |
+
+Tailwind/shadcn semantic tokens are wired to these: `--background` → `--bg`, `--foreground` → `--text`, `--primary`, `--secondary` → `--surface`, etc.
+
+### 2.3 Domain colors
+
+Duty-specific semantics (fixed per theme, not from ThemeParams):
+
+- `--duty` — duty shift (e.g. green).
+- `--unavailable` — unavailable (e.g. amber).
+- `--vacation` — vacation (e.g. blue).
+- `--today` — “today” highlight; tied to `--tg-theme-accent-text-color` / `--tg-theme-link-color`.
+
+Use Tailwind classes such as `bg-duty`, `border-l-unavailable`, `text-today`, `bg-today`, etc.
+
+### 2.4 Derived tokens (color-mix)
+
+Prefer these instead of ad-hoc color mixes:
+
+- `--surface-hover`, `--surface-hover-10` — hover states for surfaces.
+- `--surface-today-tint`, `--surface-muted-tint` — subtle tints.
+- `--today-hover`, `--today-border`, `--today-border-selected`, `--today-gradient-end` — today state.
+- `--muted-fade`, `--shadow-card`, etc.
+
+Defined in `globals.css`; use via `var(--surface-hover)` in classes (e.g. `hover:bg-[var(--surface-hover)]`).
+
+### 2.5 Rule for new work
+
+Use **only** these tokens and Tailwind/shadcn aliases (`bg-background`, `text-muted`, `bg-surface`, `text-accent`, `border-l-duty`, `bg-today`, etc.). Do not hardcode hex or RGB in new components or screens.
+
+---
+
+## 3. Layout and safe areas
+
+### 3.1 Width
+
+- **Token:** `--max-width-app: 420px` (in `@theme` in `globals.css`).
+- **Usage:** Page wrapper uses `max-w-[var(--max-width-app)]` (e.g. in `page.tsx`, `CalendarPage.tsx`, `admin/page.tsx`). Content is centred with `mx-auto`.
+
+### 3.2 Height
+
+- **Viewport:** Prefer `min-h-[var(--tg-viewport-stable-height,100vh)]` for the main content area so the Mini App fills the visible height correctly when expanded/collapsed. Fallback `100vh` when not in Telegram.
+- **Body:** In `globals.css`, `body` already has `min-height: var(--tg-viewport-stable-height, 100vh)` and `background: var(--bg)`.
+
+### 3.3 Safe area and content safe area
+
+- **Class `.content-safe`** (in `globals.css`): Applies:
+  - `padding-top: var(--tg-viewport-content-safe-area-inset-top, env(safe-area-inset-top, 0))`
+  - `padding-bottom: var(--tg-viewport-content-safe-area-inset-bottom, env(safe-area-inset-bottom, 0))`
+- Use `.content-safe` on the **root container of each page** so content is not covered by the Telegram header or bottom bar (Bot API 8.0+).
+- Lists that extend to the bottom should also account for bottom inset (e.g. `padding-bottom: var(--tg-viewport-content-safe-area-inset-bottom, 12px)` in `.container-app`).
+
+### 3.4 Sheets and modals
+
+Bottom sheets and modals that sit at the bottom of the screen must add safe area to their padding, e.g.:
+
+`pb-[calc(24px+env(safe-area-inset-bottom,0px))]`
+
+See `webapp-next/src/components/day-detail/DayDetail.tsx` for the Sheet content.
+
+---
+
+## 4. Typography and spacing
+
+### 4.1 Font
+
+- **Family:** `system-ui, -apple-system, sans-serif` (set in `globals.css` and Tailwind theme).
+
+### 4.2 Patterns from the calendar and duty list
+
+| Element | Classes / tokens |
+|--------|-------------------|
+| Month title | `text-[1.1rem]` / `sm:text-[1.25rem]`, `font-semibold` |
+| Year (above month) | `text-xs`, `text-muted` |
+| Nav buttons (prev/next month) | `size-10`, `rounded-[10px]` |
+| Calendar day cell | `text-[0.85rem]`, `rounded-lg`, `p-1` |
+| Duty timeline card | `px-2.5 py-2`, `rounded-lg` |
+
+### 4.3 Page and block spacing
+
+- Page container: `px-3 pb-6` in addition to `.content-safe`.
+- Between sections: `mb-3`, `mb-4` as appropriate.
+- Grids: `gap-1` for tight layouts (e.g. calendar grid), larger gaps where needed.
+
+---
+
+## 5. Component patterns
+
+### 5.1 Buttons
+
+- **Primary:** Use the default Button variant: `bg-primary text-primary-foreground` (from `webapp-next/src/components/ui/button.tsx`).
+- **Secondary icon buttons** (e.g. calendar nav):  
+  `bg-surface text-accent hover:bg-[var(--surface-hover)] focus-visible:outline-accent active:scale-95`  
+  with `size-10` and `rounded-[10px]`.
+- Keep focus visible (e.g. `focus-visible:outline-accent` or ring); do not remove outline without a visible replacement.
+
+### 5.2 Cards
+
+- **Background:** `bg-surface` or `bg-card` (both resolve to theme tokens).
+- **Borders:** `border`, `--border` (section separator color).
+- **Emphasis:** `var(--shadow-card)` for highlighted cards (e.g. current duty).
+- **Left stripe by type:** `border-l-[3px]` with:
+  - `border-l-duty`, `border-l-unavailable`, `border-l-vacation` for event types;
+  - `border-l-today` for “current duty” (see `.border-l-today` in `globals.css`).
+
+### 5.3 Calendar grid
+
+- **Structure:** 7 columns × 6 rows; use `role="grid"` on the container and `role="gridcell"` on each cell.
+- **Layout:** `min-h-[var(--calendar-grid-min-height)]`, cells `aspect-square` with `min-h-8`, `rounded-lg`, `gap-1`.
+- **Today:** `bg-today text-[var(--bg)]`; hover `hover:bg-[var(--today-hover)]`.
+- **Other month:** `opacity-40`, `pointer-events-none`, `bg-[var(--surface-muted-tint)]`.
+
+### 5.4 Timeline list (duties)
+
+- **Dates:** Horizontal line and vertical tick from shared CSS in `globals.css`:  
+  `.duty-timeline-date`, `.duty-timeline-date--today` (with `::before` / `::after`).
+- **Cards:** Same card rules as above; `border-l-[3px]` + type class; optional flip card for contacts (see `DutyTimelineCard.tsx`).
+
+---
+
+## 6. Motion and performance
+
+### 6.1 Timing
+
+- **Tokens:** `--transition-fast: 0.15s`, `--transition-normal: 0.25s`, `--ease-out: cubic-bezier(0.32, 0.72, 0, 1)`.
+- Use these for transitions and short animations so behaviour is consistent and predictable.
+
+### 6.2 Reduced motion
+
+- **Rule:** `@media (prefers-reduced-motion: reduce)` in `globals.css` shortens animation and transition durations globally. New animations should remain optional or short so they degrade gracefully when reduced.
+
+### 6.3 Android low-performance devices
+
+- **Detection:** `webapp-next/src/lib/telegram-android-perf.ts` reads Telegram’s User-Agent and sets `data-perf="low"` on the document root when the device performance class is LOW.
+- **CSS:** `[data-perf="low"] *` in `globals.css` minimizes animation/transition duration. Avoid adding heavy or long animations without considering this; prefer simple or no animation on low-end devices.
+
+---
+
+## 7. Accessibility
+
+- **Focus:** Use `focus-visible:outline-accent` (or equivalent ring) on interactive elements; do not remove focus outline without a visible alternative.
+- **Calendar:** Use `role="grid"` and `role="gridcell"`, `aria-label` on nav buttons (e.g. “Previous month”), and a composite `aria-label` on each day cell (date + event types). See `webapp-next/src/components/calendar/CalendarDay.tsx`.
+- **Images and inputs:** Always provide labels (per Telegram’s guidelines and WCAG).
+
+---
+
+## 8. Telegram integration
+
+- **Header and background:** On init (layout script and `use-telegram-theme.ts`), call:
+  - `setBackgroundColor('bg_color')`
+  - `setHeaderColor('bg_color')`
+  - `setBottomBarColor('bottom_bar_bg_color')` when available (Bot API 7.10+).
+- **Surface contrast:** When `--surface` equals `--bg` (e.g. some iOS OLED themes), `fixSurfaceContrast()` in `use-telegram-theme.ts` adjusts `--surface` using ThemeParams or a light color-mix so cards and panels remain visible.
+
+---
+
+## 9. Checklist for new screens and components
+
+Use this for review when adding or changing UI:
+
+- [ ] Use only design tokens from `globals.css` and Tailwind/shadcn aliases; no hardcoded colours.
+- [ ] Page wrapper has `.content-safe`, `max-w-[var(--max-width-app)]`, and appropriate min-height (viewport-stable-height or `min-h-screen` with fallback).
+- [ ] Buttons and cards follow the patterns above (variants, surfaces, border-l by type).
+- [ ] Safe area is respected for bottom padding and for sheets/modals.
+- [ ] Interactive elements and grids/lists have appropriate `aria-label`s and roles.
+- [ ] New animations respect `prefers-reduced-motion` and `data-perf="low"` (short or minimal on low-end Android).
--- a/duty_teller/api/app.py
+++ b/duty_teller/api/app.py
@@ -6,7 +6,7 @@ from datetime import date, timedelta

 import duty_teller.config as config

-from fastapi import Depends, FastAPI, Request
+from fastapi import Depends, FastAPI, HTTPException, Request
 from fastapi.middleware.cors import CORSMiddleware
 from fastapi.responses import JSONResponse, Response
 from fastapi.staticfiles import StaticFiles
@@ -14,19 +14,34 @@ from sqlalchemy.orm import Session

 from duty_teller.api.calendar_ics import get_calendar_events
 from duty_teller.api.dependencies import (
+    _lang_from_accept_language,
    fetch_duties_response,
+    get_authenticated_telegram_id_dep,
    get_db_session,
    get_validated_dates,
+    require_admin_telegram_id,
    require_miniapp_username,
 )
 from duty_teller.api.personal_calendar_ics import build_personal_ics, build_team_ics
-from duty_teller.cache import ics_calendar_cache
+from duty_teller.cache import invalidate_duty_related_caches, ics_calendar_cache
 from duty_teller.db.repository import (
    get_duties,
    get_duties_for_user,
+    get_duty_by_id,
    get_user_by_calendar_token,
+    get_users_for_admin,
+    is_admin_for_telegram_user,
+    update_duty_user,
 )
-from duty_teller.db.schemas import CalendarEvent, DutyWithUser
+from duty_teller.db.models import User
+from duty_teller.db.schemas import (
+    AdminDutyReassignBody,
+    CalendarEvent,
+    DutyInDb,
+    DutyWithUser,
+    UserForAdmin,
+)
+from duty_teller.i18n import t

 log = logging.getLogger(__name__)

@@ -283,6 +298,98 @@ def get_personal_calendar_ical(
    )


+# --- Admin API (initData + admin role required for GET /users and PATCH /duties) ---
+
+
+@app.get(
+    "/api/admin/me",
+    summary="Check admin status",
+    description=(
+        "Returns is_admin for the authenticated Mini App user. "
+        "Requires valid initData (same as /api/duties)."
+    ),
+)
+def admin_me(
+    _username: str = Depends(require_miniapp_username),
+    telegram_id: int = Depends(get_authenticated_telegram_id_dep),
+    session: Session = Depends(get_db_session),
+) -> dict:
+    """Return { is_admin: true } or { is_admin: false } for the current user."""
+    is_admin = is_admin_for_telegram_user(session, telegram_id)
+    return {"is_admin": is_admin}
+
+
+@app.get(
+    "/api/admin/users",
+    response_model=list[UserForAdmin],
+    summary="List users for admin dropdown",
+    description="Returns id, full_name, username for all users. Admin only.",
+)
+def admin_list_users(
+    _admin_telegram_id: int = Depends(require_admin_telegram_id),
+    session: Session = Depends(get_db_session),
+) -> list[UserForAdmin]:
+    """Return all users ordered by full_name for admin reassign dropdown."""
+    users = get_users_for_admin(session)
+    return [
+        UserForAdmin(
+            id=u.id,
+            full_name=u.full_name,
+            username=u.username,
+            role_id=u.role_id,
+        )
+        for u in users
+    ]
+
+
+@app.patch(
+    "/api/admin/duties/{duty_id}",
+    response_model=DutyInDb,
+    summary="Reassign duty to another user",
+    description="Update duty's user_id. Admin only. Invalidates ICS and pin caches.",
+)
+def admin_reassign_duty(
+    duty_id: int,
+    body: AdminDutyReassignBody,
+    request: Request,
+    _admin_telegram_id: int = Depends(require_admin_telegram_id),
+    session: Session = Depends(get_db_session),
+) -> DutyInDb:
+    """Reassign duty to another user; return updated duty or 404/400 with i18n detail."""
+    lang = _lang_from_accept_language(request.headers.get("Accept-Language"))
+    if duty_id <= 0 or body.user_id <= 0:
+        raise HTTPException(
+            status_code=400,
+            detail=t(lang, "api.bad_request"),
+        )
+    duty = get_duty_by_id(session, duty_id)
+    if duty is None:
+        raise HTTPException(
+            status_code=404,
+            detail=t(lang, "admin.duty_not_found"),
+        )
+    if session.get(User, body.user_id) is None:
+        raise HTTPException(
+            status_code=400,
+            detail=t(lang, "admin.user_not_found"),
+        )
+    updated = update_duty_user(
+        session, duty_id, body.user_id, commit=True
+    )
+    if updated is None:
+        raise HTTPException(
+            status_code=404,
+            detail=t(lang, "admin.duty_not_found"),
+        )
+    invalidate_duty_related_caches()
+    return DutyInDb(
+        id=updated.id,
+        user_id=updated.user_id,
+        start_at=updated.start_at,
+        end_at=updated.end_at,
+    )
+
+
 webapp_path = config.PROJECT_ROOT / "webapp-next" / "out"
 if webapp_path.is_dir():
    app.mount("/app", StaticFiles(directory=str(webapp_path), html=True), name="webapp")
--- a/duty_teller/api/dependencies.py
+++ b/duty_teller/api/dependencies.py
@@ -12,6 +12,7 @@ from duty_teller.db.repository import (
    get_duties,
    get_user_by_telegram_id,
    can_access_miniapp_for_telegram_user,
+    is_admin_for_telegram_user,
 )
 from duty_teller.db.schemas import DUTY_EVENT_TYPES, DutyWithUser
 from duty_teller.db.session import session_scope
@@ -159,6 +160,103 @@ def get_authenticated_username(
    return username or (user.full_name or "") or f"id:{telegram_user_id}"


+def get_authenticated_telegram_id(
+    request: Request,
+    x_telegram_init_data: str | None,
+    session: Session,
+) -> int:
+    """Return Telegram user id for the authenticated miniapp user; 0 if skip-auth.
+
+    Same validation as get_authenticated_username. Used to check is_admin.
+
+    Args:
+        request: FastAPI request (for Accept-Language in error messages).
+        x_telegram_init_data: Raw X-Telegram-Init-Data header value.
+        session: DB session.
+
+    Returns:
+        telegram_user_id (int). When MINI_APP_SKIP_AUTH, returns 0 (no real user).
+
+    Raises:
+        HTTPException: 403 if initData missing/invalid or user not in allowlist.
+    """
+    if config.MINI_APP_SKIP_AUTH:
+        return 0
+    init_data = (x_telegram_init_data or "").strip()
+    if not init_data:
+        log.warning("no X-Telegram-Init-Data header")
+        lang = _lang_from_accept_language(request.headers.get("Accept-Language"))
+        raise HTTPException(status_code=403, detail=t(lang, "api.open_from_telegram"))
+    max_age = config.INIT_DATA_MAX_AGE_SECONDS or None
+    telegram_user_id, username, auth_reason, lang = validate_init_data_with_reason(
+        init_data, config.BOT_TOKEN, max_age_seconds=max_age
+    )
+    if auth_reason != "ok":
+        log.warning("initData validation failed: %s", auth_reason)
+        raise HTTPException(
+            status_code=403, detail=_auth_error_detail(auth_reason, lang)
+        )
+    if telegram_user_id is None:
+        log.warning("initData valid but telegram_user_id missing")
+        raise HTTPException(status_code=403, detail=t(lang, "api.access_denied"))
+    user = get_user_by_telegram_id(session, telegram_user_id)
+    if not user:
+        log.warning(
+            "user not in DB (username=%s, telegram_id=%s)",
+            username,
+            telegram_user_id,
+        )
+        raise HTTPException(status_code=403, detail=t(lang, "api.access_denied"))
+    if not can_access_miniapp_for_telegram_user(session, telegram_user_id):
+        failed_phone = config.normalize_phone(user.phone) if user.phone else None
+        log.warning(
+            "access denied (username=%s, telegram_id=%s, phone=%s)",
+            username,
+            telegram_user_id,
+            failed_phone or "—",
+        )
+        raise HTTPException(status_code=403, detail=t(lang, "api.access_denied"))
+    return telegram_user_id
+
+
+def get_authenticated_telegram_id_dep(
+    request: Request,
+    x_telegram_init_data: Annotated[
+        str | None, Header(alias="X-Telegram-Init-Data")
+    ] = None,
+    session: Session = Depends(get_db_session),
+) -> int:
+    """FastAPI dependency: return telegram_user_id for authenticated miniapp user (0 if skip-auth)."""
+    return get_authenticated_telegram_id(request, x_telegram_init_data, session)
+
+
+def require_admin_telegram_id(
+    request: Request,
+    x_telegram_init_data: Annotated[
+        str | None, Header(alias="X-Telegram-Init-Data")
+    ] = None,
+    session: Session = Depends(get_db_session),
+) -> int:
+    """FastAPI dependency: require valid miniapp auth and admin role; return telegram_user_id.
+
+    When MINI_APP_SKIP_AUTH is True, admin routes are disabled (403).
+
+    Raises:
+        HTTPException: 403 if initData missing/invalid, user not in allowlist, or not admin.
+    """
+    if config.MINI_APP_SKIP_AUTH:
+        log.warning("Admin routes disabled when MINI_APP_SKIP_AUTH is set")
+        lang = _lang_from_accept_language(request.headers.get("Accept-Language"))
+        raise HTTPException(status_code=403, detail=t(lang, "import.admin_only"))
+    telegram_user_id = get_authenticated_telegram_id(
+        request, x_telegram_init_data, session
+    )
+    if not is_admin_for_telegram_user(session, telegram_user_id):
+        lang = _lang_from_accept_language(request.headers.get("Accept-Language"))
+        raise HTTPException(status_code=403, detail=t(lang, "import.admin_only"))
+    return telegram_user_id
+
+
 def fetch_duties_response(
    session: Session, from_date: str, to_date: str
 ) -> list[DutyWithUser]:
--- a/duty_teller/db/init.py
+++ b/duty_teller/db/init.py
@@ -4,6 +4,7 @@ from duty_teller.db.models import Base, User, Duty, Role
 from duty_teller.db.schemas import (
    UserCreate,
    UserInDb,
+    UserForAdmin,
    DutyCreate,
    DutyInDb,
    DutyWithUser,
@@ -16,11 +17,14 @@ from duty_teller.db.session import (
 )
 from duty_teller.db.repository import (
    delete_duties_in_range,
+    get_duties,
+    get_duty_by_id,
    get_or_create_user,
    get_or_create_user_by_full_name,
-    get_duties,
+    get_users_for_admin,
    insert_duty,
    set_user_phone,
+    update_duty_user,
    update_user_display_name,
 )

@@ -31,6 +35,7 @@ __all__ = [
    "Role",
    "UserCreate",
    "UserInDb",
+    "UserForAdmin",
    "DutyCreate",
    "DutyInDb",
    "DutyWithUser",
@@ -39,11 +44,14 @@ __all__ = [
    "get_session",
    "session_scope",
    "delete_duties_in_range",
+    "get_duties",
+    "get_duty_by_id",
    "get_or_create_user",
    "get_or_create_user_by_full_name",
-    "get_duties",
+    "get_users_for_admin",
    "insert_duty",
    "set_user_phone",
+    "update_duty_user",
    "update_user_display_name",
    "init_db",
 ]
--- a/duty_teller/db/repository.py
+++ b/duty_teller/db/repository.py
@@ -322,6 +322,61 @@ def delete_duties_in_range(
    return count


+def get_duty_by_id(session: Session, duty_id: int) -> Duty | None:
+    """Return duty by primary key.
+
+    Args:
+        session: DB session.
+        duty_id: Duty id (duties.id).
+
+    Returns:
+        Duty or None if not found.
+    """
+    return session.get(Duty, duty_id)
+
+
+def update_duty_user(
+    session: Session,
+    duty_id: int,
+    new_user_id: int,
+    *,
+    commit: bool = True,
+) -> Duty | None:
+    """Update the assigned user of a duty.
+
+    Args:
+        session: DB session.
+        duty_id: Duty id (duties.id).
+        new_user_id: New user id (users.id).
+        commit: If True, commit immediately. If False, caller commits.
+
+    Returns:
+        Updated Duty or None if duty not found.
+    """
+    duty = session.get(Duty, duty_id)
+    if duty is None:
+        return None
+    duty.user_id = new_user_id
+    if commit:
+        session.commit()
+        session.refresh(duty)
+    else:
+        session.flush()
+    return duty
+
+
+def get_users_for_admin(session: Session) -> list[User]:
+    """Return all users ordered by full_name for admin dropdown (id, full_name, username).
+
+    Args:
+        session: DB session.
+
+    Returns:
+        List of User instances ordered by full_name.
+    """
+    return session.query(User).order_by(User.full_name).all()
+
+
 def get_duties(
    session: Session,
    from_date: str,
--- a/duty_teller/db/schemas.py
+++ b/duty_teller/db/schemas.py
@@ -69,6 +69,21 @@ class DutyWithUser(DutyInDb):
    model_config = ConfigDict(from_attributes=True)


+class UserForAdmin(BaseModel):
+    """User summary for admin dropdown: id, full_name, username, role_id."""
+
+    id: int
+    full_name: str
+    username: str | None = None
+    role_id: int | None = None
+
+
+class AdminDutyReassignBody(BaseModel):
+    """Request body for PATCH /api/admin/duties/:id — reassign duty to another user."""
+
+    user_id: int
+
+
 class CalendarEvent(BaseModel):
    """External calendar event (e.g. holiday) for a single day."""

--- a/duty_teller/i18n/messages.py
+++ b/duty_teller/i18n/messages.py
@@ -88,6 +88,7 @@ MESSAGES: dict[str, dict[str, str]] = {
        ),
        "api.auth_invalid": "Invalid auth data",
        "api.access_denied": "Access denied",
+        "api.bad_request": "Bad request",
        "dates.bad_format": "Parameters from and to must be in YYYY-MM-DD format",
        "dates.from_after_to": "from date must not be after to",
        "dates.range_too_large": "Date range is too large. Request a shorter period.",
@@ -98,6 +99,9 @@ MESSAGES: dict[str, dict[str, str]] = {
        "current_duty.shift": "Shift",
        "current_duty.remaining": "Remaining: {hours}h {minutes}min",
        "current_duty.back": "Back to calendar",
+        "admin.duty_not_found": "Duty not found",
+        "admin.user_not_found": "User not found",
+        "admin.reassign_success": "Duty reassigned successfully",
    },
    "ru": {
        "start.greeting": "Привет! Я бот календаря дежурств. Используй /help для списка команд.",
@@ -174,6 +178,7 @@ MESSAGES: dict[str, dict[str, str]] = {
        "из которого открыт календарь (тот же бот, что в меню).",
        "api.auth_invalid": "Неверные данные авторизации",
        "api.access_denied": "Доступ запрещён",
+        "api.bad_request": "Неверный запрос",
        "dates.bad_format": "Параметры from и to должны быть в формате YYYY-MM-DD",
        "dates.from_after_to": "Дата from не должна быть позже to",
        "dates.range_too_large": "Диапазон дат слишком большой. Запросите более короткий период.",
@@ -184,5 +189,8 @@ MESSAGES: dict[str, dict[str, str]] = {
        "current_duty.shift": "Смена",
        "current_duty.remaining": "Осталось: {hours}ч {minutes}мин",
        "current_duty.back": "Назад к календарю",
+        "admin.duty_not_found": "Дежурство не найдено",
+        "admin.user_not_found": "Пользователь не найден",
+        "admin.reassign_success": "Дежурство успешно переназначено",
    },
 }
--- a/tests/test_admin_api.py
+++ b/tests/test_admin_api.py
@@ -0,0 +1,360 @@
+"""Tests for admin API: GET /api/admin/me, GET /api/admin/users, PATCH /api/admin/duties/:id."""
+
+from unittest.mock import ANY, MagicMock, patch
+
+import pytest
+from fastapi.testclient import TestClient
+
+from duty_teller.api.app import app
+
+
+@pytest.fixture
+def client():
+    return TestClient(app)
+
+
+# --- GET /api/admin/me ---
+
+
+@patch("duty_teller.api.dependencies.config.MINI_APP_SKIP_AUTH", True)
+def test_admin_me_skip_auth_returns_is_admin_false(client):
+    """With MINI_APP_SKIP_AUTH, GET /api/admin/me returns is_admin: false (no real user)."""
+    r = client.get("/api/admin/me")
+    assert r.status_code == 200
+    assert r.json() == {"is_admin": False}
+
+
+@patch("duty_teller.api.app.is_admin_for_telegram_user")
+@patch("duty_teller.api.dependencies.can_access_miniapp_for_telegram_user")
+@patch("duty_teller.api.dependencies.get_user_by_telegram_id")
+@patch("duty_teller.api.dependencies.validate_init_data_with_reason")
+@patch("duty_teller.api.dependencies.config.MINI_APP_SKIP_AUTH", False)
+def test_admin_me_returns_is_admin_true_when_admin(
+    mock_validate, mock_get_user, mock_can_access, mock_is_admin, client
+):
+    """When user is admin, GET /api/admin/me returns is_admin: true."""
+    from types import SimpleNamespace
+
+    mock_validate.return_value = (100, "user", "ok", "en")
+    mock_get_user.return_value = SimpleNamespace(full_name="Admin", username="admin")
+    mock_can_access.return_value = True
+    mock_is_admin.return_value = True
+    r = client.get("/api/admin/me", headers={"X-Telegram-Init-Data": "auth_date=1&user=%7B%22id%22%3A100%7D&hash=x"})
+    assert r.status_code == 200
+    assert r.json() == {"is_admin": True}
+
+
+@patch("duty_teller.api.app.is_admin_for_telegram_user")
+@patch("duty_teller.api.dependencies.can_access_miniapp_for_telegram_user")
+@patch("duty_teller.api.dependencies.get_user_by_telegram_id")
+@patch("duty_teller.api.dependencies.validate_init_data_with_reason")
+@patch("duty_teller.api.dependencies.config.MINI_APP_SKIP_AUTH", False)
+def test_admin_me_returns_is_admin_false_when_not_admin(
+    mock_validate, mock_get_user, mock_can_access, mock_is_admin, client
+):
+    """When user is not admin, GET /api/admin/me returns is_admin: false."""
+    from types import SimpleNamespace
+
+    mock_validate.return_value = (200, "user", "ok", "en")
+    mock_get_user.return_value = SimpleNamespace(full_name="User", username="user")
+    mock_can_access.return_value = True
+    mock_is_admin.return_value = False
+    r = client.get("/api/admin/me", headers={"X-Telegram-Init-Data": "auth_date=1&user=%7B%22id%22%3A200%7D&hash=x"})
+    assert r.status_code == 200
+    assert r.json() == {"is_admin": False}
+
+
+# --- GET /api/admin/users ---
+
+
+@patch("duty_teller.api.dependencies.config.MINI_APP_SKIP_AUTH", False)
+def test_admin_users_403_without_init_data(client):
+    """GET /api/admin/users without initData returns 403."""
+    r = client.get("/api/admin/users")
+    assert r.status_code == 403
+
+
+@patch("duty_teller.api.dependencies.is_admin_for_telegram_user")
+@patch("duty_teller.api.dependencies.can_access_miniapp_for_telegram_user")
+@patch("duty_teller.api.dependencies.get_user_by_telegram_id")
+@patch("duty_teller.api.dependencies.validate_init_data_with_reason")
+@patch("duty_teller.api.dependencies.config.MINI_APP_SKIP_AUTH", False)
+def test_admin_users_403_when_not_admin(
+    mock_validate, mock_get_user, mock_can_access, mock_is_admin, client
+):
+    """GET /api/admin/users when not admin returns 403 with admin_only message."""
+    from types import SimpleNamespace
+
+    mock_validate.return_value = (100, "u", "ok", "en")
+    mock_get_user.return_value = SimpleNamespace(full_name="U", username="u")
+    mock_can_access.return_value = True
+    mock_is_admin.return_value = False  # not admin
+    r = client.get(
+        "/api/admin/users",
+        headers={"X-Telegram-Init-Data": "auth_date=1&user=%7B%22id%22%3A100%7D&hash=x"},
+    )
+    assert r.status_code == 403
+    detail = r.json()["detail"]
+    assert "admin" in detail.lower() or "администратор" in detail or "only" in detail
+
+
+@patch("duty_teller.api.app.get_users_for_admin")
+@patch("duty_teller.api.dependencies.is_admin_for_telegram_user")
+@patch("duty_teller.api.dependencies.can_access_miniapp_for_telegram_user")
+@patch("duty_teller.api.dependencies.get_user_by_telegram_id")
+@patch("duty_teller.api.dependencies.validate_init_data_with_reason")
+@patch("duty_teller.api.dependencies.config.MINI_APP_SKIP_AUTH", False)
+def test_admin_users_200_returns_list(
+    mock_validate, mock_get_user, mock_can_access, mock_is_admin, mock_get_users, client
+):
+    """GET /api/admin/users returns list of id, full_name, username, role_id."""
+    from types import SimpleNamespace
+
+    mock_validate.return_value = (1, "admin", "ok", "en")
+    mock_get_user.return_value = SimpleNamespace(full_name="Admin", username="admin")
+    mock_can_access.return_value = True
+    mock_is_admin.return_value = True
+    mock_get_users.return_value = [
+        SimpleNamespace(id=1, full_name="Alice", username="alice", role_id=1),
+        SimpleNamespace(id=2, full_name="Bob", username=None, role_id=2),
+    ]
+    r = client.get(
+        "/api/admin/users",
+        headers={"X-Telegram-Init-Data": "auth_date=1&user=%7B%22id%22%3A1%7D&hash=x"},
+    )
+    assert r.status_code == 200
+    data = r.json()
+    assert len(data) == 2
+    assert data[0]["id"] == 1
+    assert data[0]["full_name"] == "Alice"
+    assert data[0]["username"] == "alice"
+    assert data[0]["role_id"] == 1
+    assert data[1]["id"] == 2
+    assert data[1]["full_name"] == "Bob"
+    assert data[1]["username"] is None
+    assert data[1]["role_id"] == 2
+
+
+# --- PATCH /api/admin/duties/:id ---
+
+
+@patch("duty_teller.api.dependencies.config.MINI_APP_SKIP_AUTH", False)
+def test_admin_reassign_403_without_auth(client):
+    """PATCH /api/admin/duties/1 without auth returns 403."""
+    r = client.patch(
+        "/api/admin/duties/1",
+        json={"user_id": 2},
+    )
+    assert r.status_code == 403
+
+
+@patch("duty_teller.api.app.require_admin_telegram_id")
+@patch("duty_teller.api.dependencies.config.MINI_APP_SKIP_AUTH", False)
+def test_admin_reassign_403_when_not_admin(mock_require_admin, client):
+    """PATCH /api/admin/duties/1 when not admin returns 403."""
+    from fastapi import HTTPException
+
+    from duty_teller.i18n import t
+
+    mock_require_admin.side_effect = HTTPException(
+        status_code=403, detail=t("en", "import.admin_only")
+    )
+    r = client.patch(
+        "/api/admin/duties/1",
+        json={"user_id": 2},
+        headers={"X-Telegram-Init-Data": "x"},
+    )
+    assert r.status_code == 403
+
+
+@patch("duty_teller.api.app.invalidate_duty_related_caches")
+@patch("duty_teller.api.app.update_duty_user")
+@patch("duty_teller.api.app.get_duty_by_id")
+@patch("duty_teller.api.dependencies.is_admin_for_telegram_user")
+@patch("duty_teller.api.dependencies.can_access_miniapp_for_telegram_user")
+@patch("duty_teller.api.dependencies.get_user_by_telegram_id")
+@patch("duty_teller.api.dependencies.validate_init_data_with_reason")
+@patch("duty_teller.api.dependencies.config.MINI_APP_SKIP_AUTH", False)
+def test_admin_reassign_404_when_duty_missing(
+    mock_validate,
+    mock_get_user,
+    mock_can_access,
+    mock_is_admin,
+    mock_get_duty,
+    mock_update,
+    mock_invalidate,
+    client,
+):
+    """PATCH /api/admin/duties/999 returns 404 when duty not found."""
+    from types import SimpleNamespace
+
+    mock_validate.return_value = (1, "admin", "ok", "en")
+    mock_get_user.return_value = SimpleNamespace(full_name="Admin", username="admin")
+    mock_can_access.return_value = True
+    mock_is_admin.return_value = True
+    mock_get_duty.return_value = None
+    r = client.patch(
+        "/api/admin/duties/999",
+        json={"user_id": 2},
+        headers={"X-Telegram-Init-Data": "auth_date=1&user=%7B%22id%22%3A1%7D&hash=x"},
+    )
+    assert r.status_code == 404
+    mock_update.assert_not_called()
+    mock_invalidate.assert_not_called()
+
+
+@patch("duty_teller.api.app.invalidate_duty_related_caches")
+@patch("duty_teller.api.app.update_duty_user")
+@patch("duty_teller.api.app.get_duty_by_id")
+@patch("duty_teller.api.dependencies.is_admin_for_telegram_user")
+@patch("duty_teller.api.dependencies.can_access_miniapp_for_telegram_user")
+@patch("duty_teller.api.dependencies.get_user_by_telegram_id")
+@patch("duty_teller.api.dependencies.validate_init_data_with_reason")
+@patch("duty_teller.api.dependencies.config.MINI_APP_SKIP_AUTH", False)
+def test_admin_reassign_400_when_user_not_found(
+    mock_validate,
+    mock_get_user,
+    mock_can_access,
+    mock_is_admin,
+    mock_get_duty,
+    mock_update,
+    mock_invalidate,
+    client,
+):
+    """PATCH /api/admin/duties/1 returns 400 when user_id does not exist."""
+    from types import SimpleNamespace
+
+    mock_validate.return_value = (1, "admin", "ok", "en")
+    mock_get_user.return_value = SimpleNamespace(full_name="Admin", username="admin")
+    mock_can_access.return_value = True
+    mock_is_admin.return_value = True
+    mock_get_duty.return_value = SimpleNamespace(
+        id=1, user_id=10, start_at="2026-01-15T09:00:00Z", end_at="2026-01-15T18:00:00Z"
+    )
+    mock_session = MagicMock()
+    mock_session.get.return_value = None  # User not found
+    with patch("duty_teller.api.app.get_db_session") as mock_db:
+        mock_db.return_value.__enter__.return_value = mock_session
+        mock_db.return_value.__exit__.return_value = None
+        r = client.patch(
+            "/api/admin/duties/1",
+            json={"user_id": 999},
+            headers={"X-Telegram-Init-Data": "auth_date=1&user=%7B%22id%22%3A1%7D&hash=x"},
+        )
+    assert r.status_code == 400
+    mock_update.assert_not_called()
+    mock_invalidate.assert_not_called()
+
+
+@patch("duty_teller.api.app.invalidate_duty_related_caches")
+@patch("duty_teller.api.app.update_duty_user")
+@patch("duty_teller.api.app.get_duty_by_id")
+@patch("duty_teller.api.dependencies.is_admin_for_telegram_user")
+@patch("duty_teller.api.dependencies.can_access_miniapp_for_telegram_user")
+@patch("duty_teller.api.dependencies.get_user_by_telegram_id")
+@patch("duty_teller.api.dependencies.validate_init_data_with_reason")
+@patch("duty_teller.api.dependencies.config.MINI_APP_SKIP_AUTH", False)
+def test_admin_reassign_200_updates_and_invalidates(
+    mock_validate,
+    mock_get_user,
+    mock_can_access,
+    mock_is_admin,
+    mock_get_duty,
+    mock_update_duty_user,
+    mock_invalidate,
+    client,
+):
+    """PATCH /api/admin/duties/1 with valid body returns 200 and invalidates caches."""
+    from types import SimpleNamespace
+
+    mock_validate.return_value = (1, "admin", "ok", "en")
+    mock_get_user.return_value = SimpleNamespace(full_name="Admin", username="admin")
+    mock_can_access.return_value = True
+    mock_is_admin.return_value = True
+    duty = SimpleNamespace(
+        id=1,
+        user_id=10,
+        start_at="2026-01-15T09:00:00Z",
+        end_at="2026-01-15T18:00:00Z",
+    )
+    updated_duty = SimpleNamespace(
+        id=1,
+        user_id=2,
+        start_at="2026-01-15T09:00:00Z",
+        end_at="2026-01-15T18:00:00Z",
+    )
+    mock_get_duty.return_value = duty
+    mock_update_duty_user.return_value = updated_duty
+    mock_session = MagicMock()
+    mock_session.get.return_value = SimpleNamespace(id=2)  # User exists
+    with patch("duty_teller.api.app.get_db_session") as mock_db:
+        mock_db.return_value.__enter__.return_value = mock_session
+        mock_db.return_value.__exit__.return_value = None
+        r = client.patch(
+            "/api/admin/duties/1",
+            json={"user_id": 2},
+            headers={"X-Telegram-Init-Data": "auth_date=1&user=%7B%22id%22%3A1%7D&hash=x"},
+        )
+    assert r.status_code == 200
+    data = r.json()
+    assert data["id"] == 1
+    assert data["user_id"] == 2
+    assert data["start_at"] == "2026-01-15T09:00:00Z"
+    assert data["end_at"] == "2026-01-15T18:00:00Z"
+    mock_update_duty_user.assert_called_once_with(ANY, 1, 2, commit=True)
+    mock_invalidate.assert_called_once()
+
+
+@patch("duty_teller.api.dependencies.config.MINI_APP_SKIP_AUTH", True)
+def test_admin_users_403_when_skip_auth(client):
+    """GET /api/admin/users with MINI_APP_SKIP_AUTH returns 403 (admin routes disabled)."""
+    r = client.get("/api/admin/users")
+    assert r.status_code == 403
+    detail = r.json()["detail"]
+    assert "admin" in detail.lower() or "администратор" in detail
+
+
+@patch("duty_teller.api.dependencies.config.MINI_APP_SKIP_AUTH", True)
+def test_admin_reassign_403_when_skip_auth(client):
+    """PATCH /api/admin/duties/1 with MINI_APP_SKIP_AUTH returns 403."""
+    r = client.patch(
+        "/api/admin/duties/1",
+        json={"user_id": 2},
+    )
+    assert r.status_code == 403
+
+
+@patch("duty_teller.api.app.get_duty_by_id")
+@patch("duty_teller.api.dependencies.is_admin_for_telegram_user")
+@patch("duty_teller.api.dependencies.can_access_miniapp_for_telegram_user")
+@patch("duty_teller.api.dependencies.get_user_by_telegram_id")
+@patch("duty_teller.api.dependencies.validate_init_data_with_reason")
+@patch("duty_teller.api.dependencies.config.MINI_APP_SKIP_AUTH", False)
+def test_admin_reassign_404_uses_accept_language_for_detail(
+    mock_validate,
+    mock_get_user,
+    mock_can_access,
+    mock_is_admin,
+    mock_get_duty,
+    client,
+):
+    """PATCH with Accept-Language: ru returns 404 detail in Russian."""
+    from types import SimpleNamespace
+
+    mock_validate.return_value = (1, "admin", "ok", "en")
+    mock_get_user.return_value = SimpleNamespace(full_name="Admin", username="admin")
+    mock_can_access.return_value = True
+    mock_is_admin.return_value = True
+    mock_get_duty.return_value = None
+    with patch("duty_teller.api.app._lang_from_accept_language") as mock_lang:
+        mock_lang.return_value = "ru"
+        r = client.patch(
+            "/api/admin/duties/999",
+            json={"user_id": 2},
+            headers={
+                "X-Telegram-Init-Data": "auth_date=1&user=%7B%22id%22%3A1%7D&hash=x",
+                "Accept-Language": "ru",
+            },
+        )
+    assert r.status_code == 404
+    assert r.json()["detail"] == "Дежурство не найдено"
--- a/tests/test_repository_duty_range.py
+++ b/tests/test_repository_duty_range.py
@@ -9,9 +9,12 @@ from duty_teller.db.repository import (
    delete_duties_in_range,
    get_duties,
    get_duties_for_user,
+    get_duty_by_id,
    get_or_create_user,
    get_or_create_user_by_full_name,
+    get_users_for_admin,
    insert_duty,
+    update_duty_user,
    update_user_display_name,
 )

@@ -217,6 +220,52 @@ def test_get_or_create_user_keeps_name_when_flag_true_updates_username(session):
    assert u2.username == "new_username"


+def test_get_duty_by_id_returns_duty(session, user_a):
+    """get_duty_by_id returns the duty when it exists."""
+    duty = insert_duty(
+        session, user_a.id, "2026-02-01T09:00:00Z", "2026-02-01T18:00:00Z"
+    )
+    found = get_duty_by_id(session, duty.id)
+    assert found is not None
+    assert found.id == duty.id
+    assert found.user_id == user_a.id
+    assert found.start_at == "2026-02-01T09:00:00Z"
+
+
+def test_get_duty_by_id_returns_none_when_missing(session):
+    """get_duty_by_id returns None for non-existent id."""
+    assert get_duty_by_id(session, 99999) is None
+
+
+def test_update_duty_user_changes_user(session, user_a):
+    """update_duty_user updates user_id and returns the duty."""
+    user_b = get_or_create_user_by_full_name(session, "User B")
+    duty = insert_duty(
+        session, user_a.id, "2026-02-01T09:00:00Z", "2026-02-01T18:00:00Z"
+    )
+    updated = update_duty_user(session, duty.id, user_b.id, commit=True)
+    assert updated is not None
+    assert updated.id == duty.id
+    assert updated.user_id == user_b.id
+    session.refresh(duty)
+    assert duty.user_id == user_b.id
+
+
+def test_update_duty_user_returns_none_when_duty_missing(session, user_a):
+    """update_duty_user returns None when duty does not exist."""
+    assert update_duty_user(session, 99999, user_a.id, commit=True) is None
+
+
+def test_get_users_for_admin_returns_all_ordered_by_full_name(session, user_a):
+    """get_users_for_admin returns all users ordered by full_name."""
+    get_or_create_user_by_full_name(session, "Alice")
+    get_or_create_user_by_full_name(session, "Борис")
+    users = get_users_for_admin(session)
+    assert len(users) >= 3
+    full_names = [u.full_name for u in users]
+    assert full_names == sorted(full_names)
+
+
 def test_update_user_display_name_sets_flag_then_get_or_create_user_keeps_name(session):
    """update_user_display_name sets name and flag; get_or_create_user then does not overwrite name."""
    get_or_create_user(
--- a/webapp-next/src/app/admin/page.test.tsx
+++ b/webapp-next/src/app/admin/page.test.tsx
@@ -0,0 +1,246 @@
+/**
+ * Component tests for admin page: render, access denied, duty list, reassign sheet.
+ */
+
+import { describe, it, expect, beforeEach, vi } from "vitest";
+import { render, screen, waitFor, fireEvent } from "@testing-library/react";
+import AdminPage from "./page";
+import { resetAppStore } from "@/test/test-utils";
+import { useAppStore } from "@/store/app-store";
+
+vi.mock("@/hooks/use-telegram-auth", () => ({
+  useTelegramAuth: vi.fn(),
+}));
+
+vi.mock("next/navigation", () => ({
+  useRouter: vi.fn(() => ({ push: vi.fn() })),
+}));
+
+const mockUseTelegramAuth = vi.mocked(
+  await import("@/hooks/use-telegram-auth").then((m) => m.useTelegramAuth)
+);
+
+const sampleUsers = [
+  { id: 1, full_name: "Alice", username: "alice", role_id: 1 },
+  { id: 2, full_name: "Bob", username: null, role_id: 2 },
+];
+
+const sampleDuties: Array<{
+  id: number;
+  user_id: number;
+  start_at: string;
+  end_at: string;
+  full_name: string;
+  event_type: string;
+  phone: string | null;
+  username: string | null;
+}> = [
+  {
+    id: 10,
+    user_id: 1,
+    start_at: "2030-01-15T09:00:00Z",
+    end_at: "2030-01-15T18:00:00Z",
+    full_name: "Alice",
+    event_type: "duty",
+    phone: null,
+    username: "alice",
+  },
+];
+
+function mockFetchForAdmin(
+  users: Array<{ id: number; full_name: string; username: string | null; role_id?: number }> = sampleUsers,
+  duties = sampleDuties,
+  options?: { adminMe?: { is_admin: boolean } }
+) {
+  const adminMe = options?.adminMe ?? { is_admin: true };
+  vi.stubGlobal(
+    "fetch",
+    vi.fn((url: string, init?: RequestInit) => {
+      if (url.includes("/api/admin/me")) {
+        return Promise.resolve({
+          ok: true,
+          status: 200,
+          json: () => Promise.resolve(adminMe),
+        } as Response);
+      }
+      if (url.includes("/api/admin/users")) {
+        return Promise.resolve({
+          ok: true,
+          status: 200,
+          json: () => Promise.resolve(users),
+        } as Response);
+      }
+      if (url.includes("/api/duties")) {
+        return Promise.resolve({
+          ok: true,
+          status: 200,
+          json: () => Promise.resolve(duties),
+        } as Response);
+      }
+      return Promise.reject(new Error(`Unexpected URL: ${url}`));
+    })
+  );
+}
+
+describe("AdminPage", () => {
+  beforeEach(() => {
+    resetAppStore();
+    useAppStore.getState().setCurrentMonth(new Date(2025, 0, 1));
+    mockUseTelegramAuth.mockReturnValue({
+      initDataRaw: "test-init",
+      startParam: undefined,
+      isLocalhost: true,
+    });
+  });
+
+  it("shows admin title and back link when allowed and data loaded", async () => {
+    mockFetchForAdmin();
+    render(<AdminPage />);
+    await waitFor(() => {
+      expect(screen.getByRole("heading", { name: /admin|админка/i })).toBeInTheDocument();
+    });
+    expect(screen.getByRole("link", { name: /back to calendar|назад к календарю/i })).toBeInTheDocument();
+  });
+
+  it("shows access denied when fetchAdminMe returns is_admin false", async () => {
+    mockFetchForAdmin(sampleUsers, [], { adminMe: { is_admin: false } });
+    render(<AdminPage />);
+    await waitFor(
+      () => {
+        expect(
+          screen.getByText(/Access only for administrators|Доступ только для администраторов/i)
+        ).toBeInTheDocument();
+      },
+      { timeout: 2000 }
+    );
+  });
+
+  it("shows access denied message when GET /api/admin/users returns 403", async () => {
+    vi.stubGlobal(
+      "fetch",
+      vi.fn((url: string) => {
+        if (url.includes("/api/admin/me")) {
+          return Promise.resolve({
+            ok: true,
+            status: 200,
+            json: () => Promise.resolve({ is_admin: true }),
+          } as Response);
+        }
+        if (url.includes("/api/admin/users")) {
+          return Promise.resolve({
+            ok: false,
+            status: 403,
+            json: () => Promise.resolve({ detail: "Admin only" }),
+          } as Response);
+        }
+        if (url.includes("/api/duties")) {
+          return Promise.resolve({
+            ok: true,
+            status: 200,
+            json: () => Promise.resolve([]),
+          } as Response);
+        }
+        return Promise.reject(new Error(`Unexpected: ${url}`));
+      })
+    );
+    render(<AdminPage />);
+    await waitFor(
+      () => {
+        expect(
+          screen.getByText(/Admin only|Access only for administrators|Доступ только для администраторов/i)
+        ).toBeInTheDocument();
+      },
+      { timeout: 2000 }
+    );
+  });
+
+  it("shows duty row and opens reassign sheet on click", async () => {
+    mockFetchForAdmin();
+    render(<AdminPage />);
+    await waitFor(() => {
+      expect(screen.getByText("Alice")).toBeInTheDocument();
+    });
+    const dutyButton = screen.getByRole("button", { name: /Alice/ });
+    fireEvent.click(dutyButton);
+    await waitFor(() => {
+      expect(
+        screen.getByLabelText(/select user|выберите пользователя/i)
+      ).toBeInTheDocument();
+    });
+    expect(screen.getByRole("button", { name: /save|сохранить/i })).toBeInTheDocument();
+  });
+
+  it("shows no users message in sheet when usersForSelect is empty", async () => {
+    mockFetchForAdmin([], sampleDuties);
+    render(<AdminPage />);
+    await waitFor(() => {
+      expect(screen.getByText("Alice")).toBeInTheDocument();
+    });
+    fireEvent.click(screen.getByRole("button", { name: /Alice/ }));
+    await waitFor(() => {
+      expect(
+        screen.getByText(/No users available for assignment|Нет пользователей для назначения/i)
+      ).toBeInTheDocument();
+    });
+  });
+
+  it("shows success message after successful reassign", async () => {
+    mockFetchForAdmin();
+    vi.stubGlobal(
+      "fetch",
+      vi.fn((url: string, init?: RequestInit) => {
+        if (url.includes("/api/admin/me")) {
+          return Promise.resolve({
+            ok: true,
+            status: 200,
+            json: () => Promise.resolve({ is_admin: true }),
+          } as Response);
+        }
+        if (url.includes("/api/admin/users")) {
+          return Promise.resolve({
+            ok: true,
+            status: 200,
+            json: () => Promise.resolve(sampleUsers),
+          } as Response);
+        }
+        if (url.includes("/api/duties")) {
+          return Promise.resolve({
+            ok: true,
+            status: 200,
+            json: () => Promise.resolve(sampleDuties),
+          } as Response);
+        }
+        if (url.includes("/api/admin/duties/") && init?.method === "PATCH") {
+          return Promise.resolve({
+            ok: true,
+            status: 200,
+            json: () =>
+              Promise.resolve({
+                id: 10,
+                user_id: 2,
+                start_at: "2030-01-15T09:00:00Z",
+                end_at: "2030-01-15T18:00:00Z",
+              }),
+          } as Response);
+        }
+        return Promise.reject(new Error(`Unexpected URL: ${url}`));
+      })
+    );
+    render(<AdminPage />);
+    await waitFor(() => {
+      expect(screen.getByText("Alice")).toBeInTheDocument();
+    });
+    fireEvent.click(screen.getByRole("button", { name: /Alice/ }));
+    await waitFor(() => {
+      expect(screen.getByLabelText(/select user|выберите пользователя/i)).toBeInTheDocument();
+    });
+    const select = screen.getByLabelText(/select user|выберите пользователя/i);
+    fireEvent.change(select, { target: { value: "2" } });
+    fireEvent.click(screen.getByRole("button", { name: /save|сохранить/i }));
+    await waitFor(() => {
+      expect(
+        screen.getByText(/Duty reassigned|Дежурство переназначено/i)
+      ).toBeInTheDocument();
+    });
+  });
+});
--- a/webapp-next/src/app/admin/page.tsx
+++ b/webapp-next/src/app/admin/page.tsx
@@ -0,0 +1,450 @@
+/**
+ * Admin page: list duties for the month and reassign duty to another user.
+ * Visible only to admins (link shown on calendar when GET /api/admin/me returns is_admin).
+ * Requires GET /api/admin/users and PATCH /api/admin/duties/:id (admin-only).
+ */
+
+"use client";
+
+import { useEffect, useState, useCallback, useRef } from "react";
+import Link from "next/link";
+import { useRouter } from "next/navigation";
+import { backButton } from "@telegram-apps/sdk-react";
+import { useAppStore } from "@/store/app-store";
+import { useShallow } from "zustand/react/shallow";
+import { useTelegramAuth } from "@/hooks/use-telegram-auth";
+import { useTranslation } from "@/i18n/use-translation";
+import {
+  fetchDuties,
+  fetchAdminMe,
+  fetchAdminUsers,
+  patchAdminDuty,
+  AccessDeniedError,
+  type UserForAdmin,
+} from "@/lib/api";
+import type { DutyWithUser } from "@/types";
+import {
+  firstDayOfMonth,
+  lastDayOfMonth,
+  localDateString,
+  formatHHMM,
+} from "@/lib/date-utils";
+import { Button } from "@/components/ui/button";
+import {
+  Sheet,
+  SheetContent,
+  SheetHeader,
+  SheetTitle,
+  SheetDescription,
+  SheetFooter,
+} from "@/components/ui/sheet";
+import { AccessDeniedScreen } from "@/components/states/AccessDeniedScreen";
+import { LoadingState } from "@/components/states/LoadingState";
+import { ErrorState } from "@/components/states/ErrorState";
+
+const PAGE_SIZE = 20;
+
+export default function AdminPage() {
+  const router = useRouter();
+  const { initDataRaw, isLocalhost } = useTelegramAuth();
+  const isAllowed = isLocalhost || !!initDataRaw;
+
+  const { lang } = useAppStore(useShallow((s) => ({ lang: s.lang })));
+  const { t, monthName } = useTranslation();
+
+  // Telegram BackButton: show on mount when in Mini App, navigate to calendar on click.
+  useEffect(() => {
+    if (isLocalhost) return;
+    let offClick: (() => void) | undefined;
+    try {
+      if (backButton.mount.isAvailable()) {
+        backButton.mount();
+      }
+      if (backButton.show.isAvailable()) {
+        backButton.show();
+      }
+      if (backButton.onClick.isAvailable()) {
+        offClick = backButton.onClick(() => router.push("/"));
+      }
+    } catch {
+      // Non-Telegram environment; BackButton not available.
+    }
+    return () => {
+      try {
+        if (typeof offClick === "function") offClick();
+        if (backButton.hide.isAvailable()) {
+          backButton.hide();
+        }
+      } catch {
+        // Ignore cleanup errors in non-Telegram environment.
+      }
+    };
+  }, [isLocalhost, router]);
+
+  const [users, setUsers] = useState<UserForAdmin[]>([]);
+  const [duties, setDuties] = useState<DutyWithUser[]>([]);
+  const [loadingUsers, setLoadingUsers] = useState(true);
+  const [loadingDuties, setLoadingDuties] = useState(true);
+  /** null = not yet checked, true = is admin, false = not admin (then adminAccessDenied is set). */
+  const [adminCheckComplete, setAdminCheckComplete] = useState<boolean | null>(null);
+  const [adminAccessDenied, setAdminAccessDenied] = useState(false);
+  const [adminAccessDeniedDetail, setAdminAccessDeniedDetail] = useState<string | null>(null);
+  const [error, setError] = useState<string | null>(null);
+  const [selectedDuty, setSelectedDuty] = useState<DutyWithUser | null>(null);
+  const [selectedUserId, setSelectedUserId] = useState<number | "">("");
+  const [saving, setSaving] = useState(false);
+  const [reassignError, setReassignError] = useState<string | null>(null);
+  const [successMessage, setSuccessMessage] = useState<string | null>(null);
+  const [visibleCount, setVisibleCount] = useState(PAGE_SIZE);
+  const sentinelRef = useRef<HTMLLIElement | null>(null);
+
+  const currentMonth = useAppStore((s) => s.currentMonth);
+  const from = localDateString(firstDayOfMonth(currentMonth));
+  const to = localDateString(lastDayOfMonth(currentMonth));
+
+  // Check admin status first; only then load users and duties (avoids extra 403 for non-admins).
+  useEffect(() => {
+    if (!isAllowed || !initDataRaw) return;
+    setAdminCheckComplete(null);
+    setAdminAccessDenied(false);
+    fetchAdminMe(initDataRaw, lang)
+      .then(({ is_admin }) => {
+        if (!is_admin) {
+          setAdminAccessDenied(true);
+          setAdminAccessDeniedDetail(null);
+          setAdminCheckComplete(false);
+        } else {
+          setAdminCheckComplete(true);
+        }
+      })
+      .catch(() => {
+        setAdminAccessDenied(true);
+        setAdminAccessDeniedDetail(null);
+        setAdminCheckComplete(false);
+      });
+  }, [isAllowed, initDataRaw, lang]);
+
+  useEffect(() => {
+    if (!isAllowed || !initDataRaw || adminCheckComplete !== true) return;
+
+    const controller = new AbortController();
+    setLoadingUsers(true);
+    fetchAdminUsers(initDataRaw, lang, controller.signal)
+      .then((list) => {
+        setUsers(list);
+      })
+      .catch((e) => {
+        if ((e as Error)?.name === "AbortError") return;
+        if (e instanceof AccessDeniedError) {
+          setAdminAccessDenied(true);
+          setAdminAccessDeniedDetail(e.serverDetail ?? null);
+        } else {
+          setError(e instanceof Error ? e.message : String(e));
+        }
+      })
+      .finally(() => setLoadingUsers(false));
+    return () => controller.abort();
+  }, [isAllowed, initDataRaw, lang, adminCheckComplete]);
+
+  useEffect(() => {
+    if (!isAllowed || !initDataRaw || adminCheckComplete !== true) return;
+
+    const controller = new AbortController();
+    setLoadingDuties(true);
+    setError(null);
+    fetchDuties(from, to, initDataRaw, lang, controller.signal)
+      .then((list) => setDuties(list))
+      .catch((e) => {
+        if ((e as Error)?.name === "AbortError") return;
+        setError(e instanceof Error ? e.message : String(e));
+      })
+      .finally(() => setLoadingDuties(false));
+    return () => controller.abort();
+  }, [isAllowed, initDataRaw, lang, from, to, adminCheckComplete]);
+
+  useEffect(() => {
+    setVisibleCount(PAGE_SIZE);
+  }, [from, to]);
+
+  const openReassign = useCallback((duty: DutyWithUser) => {
+    setSelectedDuty(duty);
+    setSelectedUserId(duty.user_id);
+    setReassignError(null);
+  }, []);
+
+  const closeReassign = useCallback(() => {
+    setSelectedDuty(null);
+    setSelectedUserId("");
+    setReassignError(null);
+  }, []);
+
+  const handleReassign = useCallback(() => {
+    if (!selectedDuty || selectedUserId === "" || !initDataRaw) return;
+    if (selectedUserId === selectedDuty.user_id) {
+      closeReassign();
+      return;
+    }
+    setSaving(true);
+    setReassignError(null);
+    patchAdminDuty(selectedDuty.id, selectedUserId, initDataRaw, lang)
+      .then((updated) => {
+        setDuties((prev) =>
+          prev.map((d) =>
+            d.id === updated.id
+              ? {
+                  ...d,
+                  user_id: updated.user_id,
+                  full_name:
+                    users.find((u) => u.id === updated.user_id)?.full_name ?? d.full_name,
+                }
+              : d
+          )
+        );
+        setSuccessMessage(t("admin.reassign_success"));
+        closeReassign();
+        setTimeout(() => setSuccessMessage(null), 3000);
+      })
+      .catch((e) => {
+        setReassignError(e instanceof Error ? e.message : String(e));
+      })
+      .finally(() => setSaving(false));
+  }, [selectedDuty, selectedUserId, initDataRaw, lang, users, closeReassign]);
+
+  const now = new Date();
+  const dutyOnly = duties
+    .filter(
+      (d) =>
+        d.event_type === "duty" && new Date(d.end_at) > now
+    )
+    .sort(
+      (a, b) =>
+        new Date(a.start_at).getTime() - new Date(b.start_at).getTime()
+    );
+
+  /** Users with role_id 1 (user) or 2 (admin) shown in reassign dropdown. */
+  const usersForSelect = users.filter(
+    (u) => u.role_id === 1 || u.role_id === 2
+  );
+
+  const visibleDuties = dutyOnly.slice(0, visibleCount);
+  const hasMore = visibleCount < dutyOnly.length;
+
+  useEffect(() => {
+    if (!hasMore || !sentinelRef.current) return;
+    const el = sentinelRef.current;
+    const observer = new IntersectionObserver(
+      (entries) => {
+        if (entries[0]?.isIntersecting) {
+          setVisibleCount((prev) =>
+            Math.min(prev + PAGE_SIZE, dutyOnly.length)
+          );
+        }
+      },
+      { root: null, rootMargin: "200px", threshold: 0 }
+    );
+    observer.observe(el);
+    return () => observer.disconnect();
+  }, [hasMore, dutyOnly.length]);
+
+  const loading = loadingUsers || loadingDuties;
+
+  if (!isAllowed) {
+    return (
+      <div className="content-safe mx-auto flex min-h-[var(--tg-viewport-stable-height,100vh)] w-full max-w-[var(--max-width-app)] flex-col bg-background px-3 pb-6">
+        <AccessDeniedScreen primaryAction="reload" />
+      </div>
+    );
+  }
+
+  if (isAllowed && initDataRaw && adminCheckComplete === null) {
+    return (
+      <div className="content-safe mx-auto flex min-h-[var(--tg-viewport-stable-height,100vh)] w-full max-w-[var(--max-width-app)] flex-col bg-background px-3 pb-6">
+        <div className="py-4 flex flex-col items-center gap-2">
+          <LoadingState />
+          <p className="text-sm text-muted-foreground">{t("admin.loading_users")}</p>
+        </div>
+      </div>
+    );
+  }
+
+  if (adminAccessDenied) {
+    return (
+      <div className="content-safe mx-auto flex min-h-[var(--tg-viewport-stable-height,100vh)] w-full max-w-[var(--max-width-app)] flex-col bg-background px-3 pb-6">
+        <div className="flex flex-col gap-4 py-6">
+          <p className="text-muted-foreground">{adminAccessDeniedDetail ?? t("admin.access_denied")}</p>
+          <Button asChild variant="outline">
+            <Link href="/">{t("admin.back_to_calendar")}</Link>
+          </Button>
+        </div>
+      </div>
+    );
+  }
+
+  return (
+    <div className="content-safe mx-auto flex min-h-[var(--tg-viewport-stable-height,100vh)] w-full max-w-[var(--max-width-app)] flex-col bg-background px-3 pb-6">
+      <header className="sticky top-0 z-10 flex items-center justify-between border-b bg-[var(--header-bg)] py-3">
+        <h1 className="text-lg font-semibold">
+          {t("admin.title")} — {monthName(currentMonth.getMonth())} {currentMonth.getFullYear()}
+        </h1>
+        <Button asChild variant="ghost" size="sm">
+          <Link href="/">{t("admin.back_to_calendar")}</Link>
+        </Button>
+      </header>
+
+      {successMessage && (
+        <p className="mt-3 text-sm text-[var(--duty)]" role="status">
+          {successMessage}
+        </p>
+      )}
+
+      {loading && (
+        <div className="py-4 flex flex-col items-center gap-2">
+          <LoadingState />
+          <p className="text-sm text-muted-foreground">{t("admin.loading_users")}</p>
+        </div>
+      )}
+
+      {error && !loading && (
+        <ErrorState message={error} onRetry={() => window.location.reload()} className="my-3" />
+      )}
+
+      {!loading && !error && (
+        <div className="mt-3 flex flex-col gap-2">
+          <p className="text-sm text-muted-foreground">
+            {t("admin.reassign_duty")}: {t("admin.select_user")}
+          </p>
+          {dutyOnly.length === 0 ? (
+            <p className="text-muted-foreground py-4">{t("admin.no_duties")}</p>
+          ) : (
+            <ul className="flex flex-col gap-1.5" aria-label={t("admin.list_aria")}>
+              {visibleDuties.map((duty) => {
+                const start = new Date(duty.start_at);
+                const end = new Date(duty.end_at);
+                const dateStr = localDateString(start);
+                const timeStr = `${formatHHMM(duty.start_at)} – ${formatHHMM(duty.end_at)}`;
+                return (
+                  <li key={duty.id}>
+                    <button
+                      type="button"
+                      onClick={() => openReassign(duty)}
+                      aria-label={t("admin.reassign_aria", {
+                        date: dateStr,
+                        time: timeStr,
+                        name: duty.full_name,
+                      })}
+                      className="w-full rounded-lg border border-l-[3px] border-l-duty bg-surface px-3 py-2.5 text-left text-sm transition-colors hover:bg-[var(--surface-hover)] focus-visible:outline-accent"
+                    >
+                      <span className="font-medium">{dateStr}</span>
+                      <span className="mx-2 text-muted-foreground">·</span>
+                      <span className="text-muted-foreground">{timeStr}</span>
+                      <span className="mx-2 text-muted-foreground">·</span>
+                      <span>{duty.full_name}</span>
+                    </button>
+                  </li>
+                );
+              })}
+              {hasMore && (
+                <li ref={sentinelRef} className="h-2" data-sentinel aria-hidden="true" />
+              )}
+            </ul>
+          )}
+        </div>
+      )}
+
+      {selectedDuty !== null && (
+        <Sheet open onOpenChange={(open) => !open && closeReassign()}>
+          <SheetContent
+            side="bottom"
+            className="rounded-t-2xl pt-3 max-h-[70vh] bg-[var(--surface)]"
+            overlayClassName="backdrop-blur-md"
+            showCloseButton={false}
+          >
+            <div className="relative px-4">
+              <Button
+                type="button"
+                variant="ghost"
+                size="icon"
+                className="absolute top-2 right-2 h-8 w-8 text-muted hover:text-[var(--text)] rounded-lg"
+                onClick={closeReassign}
+                aria-label={t("day_detail.close")}
+              >
+                <svg
+                  xmlns="http://www.w3.org/2000/svg"
+                  width="18"
+                  height="18"
+                  viewBox="0 0 24 24"
+                  fill="none"
+                  stroke="currentColor"
+                  strokeWidth="2"
+                  strokeLinecap="round"
+                  strokeLinejoin="round"
+                  aria-hidden
+                >
+                  <line x1="18" y1="6" x2="6" y2="18" />
+                  <line x1="6" y1="6" x2="18" y2="18" />
+                </svg>
+              </Button>
+              <div
+                className="w-10 h-1 rounded-full bg-[var(--handle-bg)] mx-auto mb-2"
+                aria-hidden
+              />
+              <SheetHeader className="p-0">
+                <SheetTitle>{t("admin.reassign_duty")}</SheetTitle>
+                <SheetDescription>{t("admin.select_user")}</SheetDescription>
+              </SheetHeader>
+              {selectedDuty && (
+                <div className="flex flex-col gap-4 pt-2 pb-4">
+                  <p className="text-sm text-muted-foreground">
+                    {localDateString(new Date(selectedDuty.start_at))}{" "}
+                    {formatHHMM(selectedDuty.start_at)} – {formatHHMM(selectedDuty.end_at)}
+                  </p>
+                  {usersForSelect.length === 0 ? (
+                    <p className="text-sm text-muted-foreground">{t("admin.no_users_for_assign")}</p>
+                  ) : (
+                    <div className="flex flex-col gap-2">
+                      <label htmlFor="admin-user-select" className="text-sm font-medium">
+                        {t("admin.select_user")}
+                      </label>
+                      <select
+                        id="admin-user-select"
+                        value={selectedUserId === "" ? "" : String(selectedUserId)}
+                        onChange={(e) => setSelectedUserId(e.target.value === "" ? "" : Number(e.target.value))}
+                        className="rounded-md border bg-background px-3 py-2 text-sm focus-visible:outline-accent"
+                        disabled={saving}
+                      >
+                        {usersForSelect.map((u) => (
+                          <option key={u.id} value={u.id}>
+                            {u.full_name}
+                            {u.username ? ` (@${u.username})` : ""}
+                          </option>
+                        ))}
+                      </select>
+                    </div>
+                  )}
+                  {reassignError && (
+                    <p className="text-sm text-destructive" role="alert">
+                      {reassignError}
+                    </p>
+                  )}
+                </div>
+              )}
+            </div>
+            <SheetFooter className="flex-row justify-end gap-2">
+              <Button
+                onClick={handleReassign}
+                disabled={
+                  saving ||
+                  selectedUserId === "" ||
+                  selectedUserId === selectedDuty?.user_id ||
+                  usersForSelect.length === 0
+                }
+              >
+                {saving ? t("loading") : t("admin.save")}
+              </Button>
+            </SheetFooter>
+          </SheetContent>
+        </Sheet>
+      )}
+    </div>
+  );
+}
--- a/webapp-next/src/app/global-error.tsx
+++ b/webapp-next/src/app/global-error.tsx
@@ -31,7 +31,7 @@ export default function GlobalError({
        />
      </head>
      <body className="antialiased">
-        <div className="flex min-h-screen flex-col items-center justify-center gap-4 bg-background px-4 text-foreground">
+        <div className="flex min-h-[var(--tg-viewport-stable-height,100vh)] flex-col items-center justify-center gap-4 bg-background px-4 text-foreground">
          <h1 className="text-xl font-semibold">
            {translate(lang, "error_boundary.message")}
          </h1>
--- a/webapp-next/src/app/not-found.tsx
+++ b/webapp-next/src/app/not-found.tsx
@@ -11,7 +11,7 @@ import { useTranslation } from "@/i18n/use-translation";
 export default function NotFound() {
  const { t } = useTranslation();
  return (
-    <div className="flex min-h-screen flex-col items-center justify-center gap-4 bg-background px-4 text-foreground">
+    <div className="flex min-h-[var(--tg-viewport-stable-height,100vh)] flex-col items-center justify-center gap-4 bg-background px-4 text-foreground">
      <h1 className="text-xl font-semibold">{t("not_found.title")}</h1>
      <p className="text-muted-foreground">{t("not_found.description")}</p>
      <Link
--- a/webapp-next/src/app/page.tsx
+++ b/webapp-next/src/app/page.tsx
@@ -12,6 +12,8 @@ import { useTelegramTheme } from "@/hooks/use-telegram-theme";
 import { useTelegramAuth } from "@/hooks/use-telegram-auth";
 import { useAppInit } from "@/hooks/use-app-init";
 import { callMiniAppReadyOnce } from "@/lib/telegram-ready";
+import { fetchAdminMe } from "@/lib/api";
+import { getLang } from "@/i18n/messages";
 import { AccessDeniedScreen } from "@/components/states/AccessDeniedScreen";
 import { CurrentDutyView } from "@/components/current-duty/CurrentDutyView";
 import { CalendarPage } from "@/components/CalendarPage";
@@ -24,6 +26,15 @@ export default function Home() {

  useAppInit({ isAllowed, startParam });

+  const setIsAdmin = useAppStore((s) => s.setIsAdmin);
+  useEffect(() => {
+    if (!isAllowed || !initDataRaw) {
+      setIsAdmin(false);
+      return;
+    }
+    fetchAdminMe(initDataRaw, getLang()).then(({ is_admin }) => setIsAdmin(is_admin));
+  }, [isAllowed, initDataRaw, setIsAdmin]);
+
  const { accessDenied, currentView, setCurrentView, setSelectedDay, appContentReady } =
    useAppStore(
      useShallow((s: AppState) => ({
@@ -50,7 +61,7 @@ export default function Home() {
  const content = accessDenied ? (
    <AccessDeniedScreen primaryAction="reload" />
  ) : currentView === "currentDuty" ? (
-    <div className="content-safe mx-auto flex min-h-screen w-full max-w-[var(--max-width-app)] flex-col bg-background px-3 pb-6">
+    <div className="content-safe mx-auto flex min-h-[var(--tg-viewport-stable-height,100vh)] w-full max-w-[var(--max-width-app)] flex-col bg-background px-3 pb-6">
      <CurrentDutyView
        onBack={handleBackFromCurrentDuty}
        openedFromPin={startParam === "duty"}
--- a/webapp-next/src/components/CalendarPage.tsx
+++ b/webapp-next/src/components/CalendarPage.tsx
@@ -6,12 +6,14 @@
 "use client";

 import { useRef, useState, useEffect, useCallback } from "react";
+import Link from "next/link";
 import { useAppStore } from "@/store/app-store";
 import { useShallow } from "zustand/react/shallow";
 import { useMonthData } from "@/hooks/use-month-data";
 import { useSwipe } from "@/hooks/use-swipe";
 import { useStickyScroll } from "@/hooks/use-sticky-scroll";
 import { useAutoRefresh } from "@/hooks/use-auto-refresh";
+import { useTranslation } from "@/i18n/use-translation";
 import { CalendarHeader } from "@/components/calendar/CalendarHeader";
 import { CalendarGrid } from "@/components/calendar/CalendarGrid";
 import { DutyList } from "@/components/duty/DutyList";
@@ -53,6 +55,7 @@ export function CalendarPage({ isAllowed, initDataRaw }: CalendarPageProps) {
    duties,
    calendarEvents,
    selectedDay,
+    isAdmin,
    nextMonth,
    prevMonth,
    setCurrentMonth,
@@ -68,6 +71,7 @@ export function CalendarPage({ isAllowed, initDataRaw }: CalendarPageProps) {
      duties: s.duties,
      calendarEvents: s.calendarEvents,
      selectedDay: s.selectedDay,
+      isAdmin: s.isAdmin,
      nextMonth: s.nextMonth,
      prevMonth: s.prevMonth,
      setCurrentMonth: s.setCurrentMonth,
@@ -76,6 +80,8 @@ export function CalendarPage({ isAllowed, initDataRaw }: CalendarPageProps) {
    }))
  );

+  const { t } = useTranslation();
+
  const { retry } = useMonthData({
    initDataRaw,
    enabled: isAllowed,
@@ -133,7 +139,7 @@ export function CalendarPage({ isAllowed, initDataRaw }: CalendarPageProps) {
  }, [loading, accessDenied, setAppContentReady]);

  return (
-    <div className="content-safe mx-auto flex min-h-screen w-full max-w-[var(--max-width-app)] flex-col bg-background px-3 pb-6">
+    <div className="content-safe mx-auto flex min-h-[var(--tg-viewport-stable-height,100vh)] w-full max-w-[var(--max-width-app)] flex-col bg-background px-3 pb-6">
      <div
        ref={calendarStickyRef}
        className="sticky top-0 z-10 min-h-[var(--calendar-block-min-height)] bg-background pb-2"
@@ -143,6 +149,16 @@ export function CalendarPage({ isAllowed, initDataRaw }: CalendarPageProps) {
          disabled={navDisabled}
          onPrevMonth={handlePrevMonth}
          onNextMonth={handleNextMonth}
+          trailingContent={
+            isAdmin ? (
+              <Link
+                href="/admin"
+                className="text-sm text-accent hover:underline focus-visible:outline-accent rounded"
+              >
+                {t("admin.link")}
+              </Link>
+            ) : undefined
+          }
        />
        <CalendarGrid
          currentMonth={currentMonth}
--- a/webapp-next/src/components/calendar/CalendarHeader.tsx
+++ b/webapp-next/src/components/calendar/CalendarHeader.tsx
@@ -5,6 +5,7 @@

 "use client";

+import type { ReactNode } from "react";
 import { Button } from "@/components/ui/button";
 import { useTranslation } from "@/i18n/use-translation";
 import { cn } from "@/lib/utils";
@@ -20,6 +21,8 @@ export interface CalendarHeaderProps {
  disabled?: boolean;
  onPrevMonth: () => void;
  onNextMonth: () => void;
+  /** Optional content shown above the nav row (e.g. Admin link). */
+  trailingContent?: ReactNode;
  className?: string;
 }

@@ -28,6 +31,7 @@ export function CalendarHeader({
  disabled = false,
  onPrevMonth,
  onNextMonth,
+  trailingContent,
  className,
 }: CalendarHeaderProps) {
  const { t, monthName, weekdayLabels } = useTranslation();
@@ -37,6 +41,9 @@ export function CalendarHeader({

  return (
    <header className={cn("flex flex-col", className)}>
+      {trailingContent != null && (
+        <div className="flex justify-end mb-1 min-h-[1.5rem]">{trailingContent}</div>
+      )}
      <div className="flex items-center justify-between mb-3">
        <Button
          type="button"
--- a/webapp-next/src/components/day-detail/DayDetail.tsx
+++ b/webapp-next/src/components/day-detail/DayDetail.tsx
@@ -204,7 +204,7 @@ export const DayDetail = React.forwardRef<DayDetailHandle, DayDetailProps>(
      <SheetContent
        side="bottom"
        className={cn(
-          "rounded-t-2xl pt-3 pb-[calc(24px+env(safe-area-inset-bottom,0px))] max-h-[70vh] bg-[var(--surface)]",
+          "rounded-t-2xl pt-3 max-h-[70vh] bg-[var(--surface)]",
          className
        )}
        overlayClassName="backdrop-blur-md"
--- a/webapp-next/src/components/states/AccessDeniedScreen.tsx
+++ b/webapp-next/src/components/states/AccessDeniedScreen.tsx
@@ -60,7 +60,7 @@ export function AccessDeniedScreen({

  return (
    <div
-      className="flex min-h-screen flex-col items-center justify-center gap-4 bg-background px-4 text-foreground"
+      className="flex min-h-[var(--tg-viewport-stable-height,100vh)] flex-col items-center justify-center gap-4 bg-background px-4 text-foreground"
      role="alert"
    >
      <h1 className="text-xl font-semibold">
--- a/webapp-next/src/components/ui/sheet.tsx
+++ b/webapp-next/src/components/ui/sheet.tsx
@@ -94,7 +94,7 @@ function SheetContent({
          side === "top" &&
            "inset-x-0 top-0 h-auto border-b data-[state=closed]:slide-out-to-top data-[state=open]:slide-in-from-top",
          side === "bottom" &&
-            "inset-x-0 bottom-0 h-auto border-t data-[state=closed]:slide-out-to-bottom data-[state=open]:slide-in-from-bottom",
+            "inset-x-0 bottom-0 h-auto border-t pb-[calc(24px+var(--tg-viewport-content-safe-area-inset-bottom,env(safe-area-inset-bottom,0px)))] data-[state=closed]:slide-out-to-bottom data-[state=open]:slide-in-from-bottom",
          className
        )}
        {...props}
--- a/webapp-next/src/components/ui/tooltip.tsx
+++ b/webapp-next/src/components/ui/tooltip.tsx
@@ -42,7 +42,7 @@ function TooltipContent({
        data-slot="tooltip-content"
        sideOffset={sideOffset}
        className={cn(
-          "z-50 w-fit max-w-[min(98vw,380px)] origin-(--radix-tooltip-content-transform-origin) animate-in rounded-lg bg-surface px-3 py-2 text-[0.85rem] leading-snug text-[var(--text)] shadow-[0_4px_12px_rgba(0,0,0,0.4)] fade-in-0 zoom-in-95 data-[side=bottom]:slide-in-from-top-2 data-[side=left]:slide-in-from-right-2 data-[side=right]:slide-in-from-left-2 data-[side=top]:slide-in-from-bottom-2 data-[state=closed]:animate-out data-[state=closed]:fade-out-0 data-[state=closed]:zoom-out-95",
+          "z-50 w-fit max-w-[min(98vw,380px)] origin-(--radix-tooltip-content-transform-origin) animate-in rounded-lg bg-surface px-3 py-2 text-[0.85rem] leading-snug text-[var(--text)] shadow-[var(--shadow-card)] fade-in-0 zoom-in-95 data-[side=bottom]:slide-in-from-top-2 data-[side=left]:slide-in-from-right-2 data-[side=right]:slide-in-from-left-2 data-[side=top]:slide-in-from-bottom-2 data-[state=closed]:animate-out data-[state=closed]:fade-out-0 data-[state=closed]:zoom-out-95",
          className
        )}
        {...props}
--- a/webapp-next/src/i18n/messages.ts
+++ b/webapp-next/src/i18n/messages.ts
@@ -82,6 +82,21 @@ export const MESSAGES: Record<Lang, Record<string, string>> = {
    "not_found.open_calendar": "Open calendar",
    "access_denied.hint": "Open the app again from Telegram.",
    "access_denied.reload": "Reload",
+    "admin.link": "Admin",
+    "admin.title": "Admin",
+    "admin.reassign_duty": "Reassign duty",
+    "admin.select_user": "Select user",
+    "admin.reassign_success": "Duty reassigned",
+    "admin.access_denied": "Access only for administrators.",
+    "admin.duty_not_found": "Duty not found",
+    "admin.user_not_found": "User not found",
+    "admin.back_to_calendar": "Back to calendar",
+    "admin.loading_users": "Loading users…",
+    "admin.no_duties": "No duties this month.",
+    "admin.no_users_for_assign": "No users available for assignment.",
+    "admin.save": "Save",
+    "admin.list_aria": "List of duties to reassign",
+    "admin.reassign_aria": "Reassign duty: {date}, {time}, {name}",
  },
  ru: {
    "app.title": "Календарь дежурств",
@@ -159,6 +174,21 @@ export const MESSAGES: Record<Lang, Record<string, string>> = {
    "not_found.open_calendar": "Открыть календарь",
    "access_denied.hint": "Откройте приложение снова из Telegram.",
    "access_denied.reload": "Обновить",
+    "admin.link": "Админка",
+    "admin.title": "Админка",
+    "admin.reassign_duty": "Переназначить дежурного",
+    "admin.select_user": "Выберите пользователя",
+    "admin.reassign_success": "Дежурство переназначено",
+    "admin.access_denied": "Доступ только для администраторов.",
+    "admin.duty_not_found": "Дежурство не найдено",
+    "admin.user_not_found": "Пользователь не найден",
+    "admin.back_to_calendar": "Назад к календарю",
+    "admin.loading_users": "Загрузка пользователей…",
+    "admin.no_duties": "В этом месяце дежурств нет.",
+    "admin.no_users_for_assign": "Нет пользователей для назначения.",
+    "admin.save": "Сохранить",
+    "admin.list_aria": "Список дежурств для перераспределения",
+    "admin.reassign_aria": "Переназначить дежурство: {date}, {time}, {name}",
  },
 };

--- a/webapp-next/src/lib/api.test.ts
+++ b/webapp-next/src/lib/api.test.ts
@@ -4,7 +4,14 @@
 */

 import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
-import { fetchDuties, fetchCalendarEvents, AccessDeniedError } from "./api";
+import {
+  fetchDuties,
+  fetchCalendarEvents,
+  fetchAdminMe,
+  fetchAdminUsers,
+  patchAdminDuty,
+  AccessDeniedError,
+} from "./api";

 describe("fetchDuties", () => {
  const originalFetch = globalThis.fetch;
@@ -174,3 +181,160 @@ describe("fetchCalendarEvents", () => {
    ).rejects.toMatchObject({ name: "AbortError" });
  });
 });
+
+describe("fetchAdminMe", () => {
+  const originalFetch = globalThis.fetch;
+
+  beforeEach(() => {
+    vi.stubGlobal("fetch", vi.fn());
+    (globalThis.fetch as ReturnType<typeof vi.fn>).mockResolvedValue({
+      ok: true,
+      status: 200,
+      json: () => Promise.resolve({ is_admin: true }),
+    } as Response);
+  });
+
+  afterEach(() => {
+    vi.stubGlobal("fetch", originalFetch);
+  });
+
+  it("returns is_admin true on 200", async () => {
+    const result = await fetchAdminMe("init-data", "en");
+    expect(result).toEqual({ is_admin: true });
+  });
+
+  it("returns is_admin false on 403", async () => {
+    (globalThis.fetch as ReturnType<typeof vi.fn>).mockResolvedValue({
+      ok: false,
+      status: 403,
+    } as Response);
+    const result = await fetchAdminMe("init-data", "en");
+    expect(result).toEqual({ is_admin: false });
+  });
+
+  it("returns is_admin false on non-200 and non-403", async () => {
+    (globalThis.fetch as ReturnType<typeof vi.fn>).mockResolvedValue({
+      ok: false,
+      status: 500,
+    } as Response);
+    const result = await fetchAdminMe("init-data", "en");
+    expect(result).toEqual({ is_admin: false });
+  });
+
+  it("returns is_admin false when response is not boolean", async () => {
+    (globalThis.fetch as ReturnType<typeof vi.fn>).mockResolvedValue({
+      ok: true,
+      status: 200,
+      json: () => Promise.resolve({ is_admin: "yes" }),
+    } as Response);
+    const result = await fetchAdminMe("init-data", "en");
+    expect(result).toEqual({ is_admin: false });
+  });
+});
+
+describe("fetchAdminUsers", () => {
+  const originalFetch = globalThis.fetch;
+  const validUsers = [
+    { id: 1, full_name: "Alice", username: "alice", role_id: 1 },
+    { id: 2, full_name: "Bob", username: null, role_id: 2 },
+  ];
+
+  beforeEach(() => {
+    vi.stubGlobal("fetch", vi.fn());
+    (globalThis.fetch as ReturnType<typeof vi.fn>).mockResolvedValue({
+      ok: true,
+      status: 200,
+      json: () => Promise.resolve(validUsers),
+    } as Response);
+  });
+
+  afterEach(() => {
+    vi.stubGlobal("fetch", originalFetch);
+  });
+
+  it("returns users array on 200", async () => {
+    const result = await fetchAdminUsers("init-data", "en");
+    expect(result).toEqual(validUsers);
+  });
+
+  it("throws AccessDeniedError on 403", async () => {
+    (globalThis.fetch as ReturnType<typeof vi.fn>).mockResolvedValue({
+      ok: false,
+      status: 403,
+      json: () => Promise.resolve({ detail: "Admin only" }),
+    } as Response);
+    await expect(fetchAdminUsers("init-data", "en")).rejects.toThrow(AccessDeniedError);
+    await expect(fetchAdminUsers("init-data", "en")).rejects.toMatchObject({
+      message: "ACCESS_DENIED",
+      serverDetail: "Admin only",
+    });
+  });
+
+  it("filters invalid items from response", async () => {
+    (globalThis.fetch as ReturnType<typeof vi.fn>).mockResolvedValue({
+      ok: true,
+      status: 200,
+      json: () =>
+        Promise.resolve([
+          validUsers[0],
+          { id: 2, full_name: "Bob", username: 123, role_id: 2 },
+          { id: 3 },
+        ]),
+    } as Response);
+    const result = await fetchAdminUsers("init-data", "en");
+    expect(result).toEqual([validUsers[0]]);
+  });
+});
+
+describe("patchAdminDuty", () => {
+  const originalFetch = globalThis.fetch;
+  const updatedDuty = {
+    id: 5,
+    user_id: 2,
+    start_at: "2025-03-01T09:00:00Z",
+    end_at: "2025-03-01T18:00:00Z",
+  };
+
+  beforeEach(() => {
+    vi.stubGlobal("fetch", vi.fn());
+    (globalThis.fetch as ReturnType<typeof vi.fn>).mockResolvedValue({
+      ok: true,
+      status: 200,
+      json: () => Promise.resolve(updatedDuty),
+    } as Response);
+  });
+
+  afterEach(() => {
+    vi.stubGlobal("fetch", originalFetch);
+  });
+
+  it("sends PATCH with user_id and returns updated duty", async () => {
+    const result = await patchAdminDuty(5, 2, "init-data", "en");
+    expect(result).toEqual(updatedDuty);
+    const fetchCall = (globalThis.fetch as ReturnType<typeof vi.fn>).mock.calls[0];
+    expect(fetchCall[1]?.method).toBe("PATCH");
+    expect(fetchCall[1]?.body).toBe(JSON.stringify({ user_id: 2 }));
+  });
+
+  it("throws AccessDeniedError on 403", async () => {
+    (globalThis.fetch as ReturnType<typeof vi.fn>).mockResolvedValue({
+      ok: false,
+      status: 403,
+      json: () => Promise.resolve({ detail: "Admin only" }),
+    } as Response);
+    await expect(
+      patchAdminDuty(5, 2, "init-data", "en")
+    ).rejects.toThrow(AccessDeniedError);
+  });
+
+  it("throws with server detail on 400", async () => {
+    (globalThis.fetch as ReturnType<typeof vi.fn>).mockResolvedValue({
+      ok: false,
+      status: 400,
+      json: () => Promise.resolve({ detail: "User not found" }),
+    } as Response);
+    await expect(
+      patchAdminDuty(5, 999, "init-data", "en")
+    ).rejects.toThrow("User not found");
+  });
+});
--- a/webapp-next/src/lib/api.ts
+++ b/webapp-next/src/lib/api.ts
@@ -11,6 +11,22 @@ import { translate } from "@/i18n/messages";

 type ApiLang = "ru" | "en";

+/** User summary for admin dropdown (GET /api/admin/users). */
+export interface UserForAdmin {
+  id: number;
+  full_name: string;
+  username: string | null;
+  role_id: number | null;
+}
+
+/** Minimal duty shape returned by PATCH /api/admin/duties/:id. */
+export interface DutyReassignResponse {
+  id: number;
+  user_id: number;
+  start_at: string;
+  end_at: string;
+}
+
 /** Minimal runtime check for a single duty item (required fields). */
 function isDutyWithUser(x: unknown): x is DutyWithUser {
  if (!x || typeof x !== "object") return false;
@@ -207,3 +223,153 @@ export async function fetchCalendarEvents(
    opts.cleanup();
  }
 }
+
+/**
+ * Fetch admin status for the current user (GET /api/admin/me).
+ * Returns { is_admin: true } or { is_admin: false }. On 403, treat as not admin.
+ */
+export async function fetchAdminMe(
+  initData: string,
+  acceptLang: ApiLang
+): Promise<{ is_admin: boolean }> {
+  const base =
+    typeof window !== "undefined" ? window.location.origin : "";
+  const url = `${base}/api/admin/me`;
+  const opts = buildFetchOptions(initData, acceptLang);
+  try {
+    logger.debug("API request", "/api/admin/me");
+    const res = await fetch(url, { headers: opts.headers, signal: opts.signal });
+    if (res.status === 403) {
+      return { is_admin: false };
+    }
+    if (!res.ok) {
+      return { is_admin: false };
+    }
+    const data = (await res.json()) as { is_admin?: boolean };
+    return {
+      is_admin: typeof data?.is_admin === "boolean" ? data.is_admin : false,
+    };
+  } catch (e) {
+    logger.warn("API request failed", "/api/admin/me", e);
+    return { is_admin: false };
+  } finally {
+    opts.cleanup();
+  }
+}
+
+/**
+ * Fetch users for admin dropdown (GET /api/admin/users). Admin only; throws AccessDeniedError on 403.
+ */
+export async function fetchAdminUsers(
+  initData: string,
+  acceptLang: ApiLang,
+  signal?: AbortSignal | null
+): Promise<UserForAdmin[]> {
+  const base =
+    typeof window !== "undefined" ? window.location.origin : "";
+  const url = `${base}/api/admin/users`;
+  const opts = buildFetchOptions(initData, acceptLang, signal);
+  try {
+    logger.debug("API request", "/api/admin/users");
+    const res = await fetch(url, { headers: opts.headers, signal: opts.signal });
+    if (res.status === 403) {
+      let detail = translate(acceptLang, "admin.access_denied");
+      try {
+        const body = await res.json();
+        if (body && (body as { detail?: string }).detail !== undefined) {
+          const d = (body as { detail: string | { msg?: string } }).detail;
+          detail =
+            typeof d === "string" ? d : (d.msg ?? JSON.stringify(d));
+        }
+      } catch {
+        /* ignore */
+      }
+      throw new AccessDeniedError(API_ACCESS_DENIED, detail);
+    }
+    if (!res.ok) {
+      throw new Error(translate(acceptLang, "error_load_failed"));
+    }
+    const data = await res.json();
+    if (!Array.isArray(data)) return [];
+    return data.filter(
+      (x: unknown): x is UserForAdmin =>
+        x != null &&
+        typeof (x as UserForAdmin).id === "number" &&
+        typeof (x as UserForAdmin).full_name === "string" &&
+        ((x as UserForAdmin).username === null ||
+          typeof (x as UserForAdmin).username === "string") &&
+        ((x as UserForAdmin).role_id === null ||
+          typeof (x as UserForAdmin).role_id === "number")
+    );
+  } catch (e) {
+    if ((e as Error).name === "AbortError" || e instanceof AccessDeniedError) {
+      throw e;
+    }
+    logger.error("API request failed", "/api/admin/users", e);
+    throw e;
+  } finally {
+    opts.cleanup();
+  }
+}
+
+/**
+ * Reassign a duty to another user (PATCH /api/admin/duties/:id). Admin only.
+ * Returns updated duty (id, user_id, start_at, end_at). Throws on 403/404/400.
+ */
+export async function patchAdminDuty(
+  dutyId: number,
+  userId: number,
+  initData: string,
+  acceptLang: ApiLang
+): Promise<DutyReassignResponse> {
+  const base =
+    typeof window !== "undefined" ? window.location.origin : "";
+  const url = `${base}/api/admin/duties/${dutyId}`;
+  const opts = buildFetchOptions(initData, acceptLang);
+  try {
+    logger.debug("API request", "PATCH", url, { user_id: userId });
+    const res = await fetch(url, {
+      method: "PATCH",
+      headers: {
+        ...opts.headers,
+        "Content-Type": "application/json",
+      },
+      body: JSON.stringify({ user_id: userId }),
+      signal: opts.signal,
+    });
+    if (res.status === 403) {
+      let detail = translate(acceptLang, "admin.access_denied");
+      try {
+        const body = await res.json();
+        if (body && (body as { detail?: string }).detail !== undefined) {
+          const d = (body as { detail: string | { msg?: string } }).detail;
+          detail =
+            typeof d === "string" ? d : (d.msg ?? JSON.stringify(d));
+        }
+      } catch {
+        /* ignore */
+      }
+      throw new AccessDeniedError(API_ACCESS_DENIED, detail);
+    }
+    const data = await res.json().catch(() => ({}));
+    if (!res.ok) {
+      const msg =
+        data && typeof (data as { detail?: string }).detail === "string"
+          ? (data as { detail: string }).detail
+          : translate(acceptLang, "error_generic");
+      throw new Error(msg);
+    }
+    const out = data as DutyReassignResponse;
+    if (
+      typeof out?.id !== "number" ||
+      typeof out?.user_id !== "number" ||
+      typeof out?.start_at !== "string" ||
+      typeof out?.end_at !== "string"
+    ) {
+      throw new Error(translate(acceptLang, "error_load_failed"));
+    }
+    return out;
+  } finally {
+    opts.cleanup();
+  }
+}
--- a/webapp-next/src/store/app-store.ts
+++ b/webapp-next/src/store/app-store.ts
@@ -30,6 +30,8 @@ export interface AppState {
  selectedDay: string | null;
  /** True when the first visible screen has finished loading; used to hide content until ready(). */
  appContentReady: boolean;
+  /** True when GET /api/admin/me returned is_admin: true; used to show Admin link. */
+  isAdmin: boolean;

  setCurrentMonth: (d: Date) => void;
  nextMonth: () => void;
@@ -44,8 +46,9 @@ export interface AppState {
  setCurrentView: (v: CurrentView) => void;
  setSelectedDay: (key: string | null) => void;
  setAppContentReady: (v: boolean) => void;
+  setIsAdmin: (v: boolean) => void;
  /** Batch multiple state updates into a single re-render. */
-  batchUpdate: (partial: Partial<Pick<AppState, "currentMonth" | "pendingMonth" | "lang" | "duties" | "calendarEvents" | "dataForMonthKey" | "loading" | "error" | "accessDenied" | "accessDeniedDetail" | "currentView" | "selectedDay" | "appContentReady">>) => void;
+  batchUpdate: (partial: Partial<Pick<AppState, "currentMonth" | "pendingMonth" | "lang" | "duties" | "calendarEvents" | "dataForMonthKey" | "loading" | "error" | "accessDenied" | "accessDeniedDetail" | "currentView" | "selectedDay" | "appContentReady" | "isAdmin">>) => void;
 }

 const now = new Date();
@@ -71,6 +74,7 @@ export const useAppStore = create<AppState>((set) => ({
  currentView: getInitialView(),
  selectedDay: null,
  appContentReady: false,
+  isAdmin: false,

  setCurrentMonth: (d) => set({ currentMonth: d }),
  nextMonth: () =>
@@ -91,5 +95,6 @@ export const useAppStore = create<AppState>((set) => ({
  setCurrentView: (v) => set({ currentView: v }),
  setSelectedDay: (key) => set({ selectedDay: key }),
  setAppContentReady: (v) => set({ appContentReady: v }),
+  setIsAdmin: (v) => set({ isAdmin: v }),
  batchUpdate: (partial) => set(partial),
 }));