diff --git a/backend/app/api/v1/cadastral.py b/backend/app/api/v1/cadastral.py
new file mode 100644
index 00000000..a1b17b0f
--- /dev/null
+++ b/backend/app/api/v1/cadastral.py
@@ -0,0 +1,101 @@
+"""Cadastral lookup endpoints — reverse geocode via cad_buildings.
+
+Used by trade-in backend (and potentially other internal services) to resolve
+координаты → адрес жилого дома без зависимости от внешних геокодеров.
+"""
+
+from __future__ import annotations
+
+import logging
+from typing import Annotated
+
+from fastapi import APIRouter, Depends, HTTPException, Query
+from pydantic import BaseModel
+from sqlalchemy import text
+from sqlalchemy.orm import Session
+
+from app.core.db import get_db
+
+logger = logging.getLogger(__name__)
+
+router = APIRouter()
+
+
+class CadastralReverseResult(BaseModel):
+    address: str
+    lat: float
+    lon: float
+    distance_m: float
+    cad_num: str | None = None
+
+
+@router.get("/reverse", response_model=CadastralReverseResult)
+async def reverse(
+    lat: Annotated[float, Query(ge=-90, le=90)],
+    lon: Annotated[float, Query(ge=-180, le=180)],
+    radius_m: Annotated[int, Query(ge=10, le=2000)] = 200,
+    db: Annotated[Session, Depends(get_db)] = None,  # type: ignore[assignment]
+) -> CadastralReverseResult:
+    """Координаты → ближайшее здание из cad_buildings.
+
+    Filters out гаражи/СНТ/садовод/товарищества — для trade-in нужны жилые дома.
+
+    Returns 404 если в радиусе нет подходящего здания.
+    """
+    row = db.execute(
+        text(
+            """
+            SELECT
+                readable_address,
+                cad_num,
+                ST_Y(ST_Centroid(geom)) AS lat,
+                ST_X(ST_Centroid(geom)) AS lon,
+                ST_Distance(
+                    geom::geography,
+                    ST_SetSRID(
+                        ST_MakePoint(
+                            CAST(:lon AS double precision),
+                            CAST(:lat AS double precision)
+                        ),
+                        4326
+                    )::geography
+                ) AS distance_m
+            FROM cad_buildings
+            WHERE ST_DWithin(
+                geom::geography,
+                ST_SetSRID(
+                    ST_MakePoint(
+                        CAST(:lon AS double precision),
+                        CAST(:lat AS double precision)
+                    ),
+                    4326
+                )::geography,
+                CAST(:radius AS double precision)
+            )
+            AND readable_address !~* '(гараж|снт|садовод|товарищ|уч\\.)'
+            ORDER BY ST_Distance(
+                geom::geography,
+                ST_SetSRID(
+                    ST_MakePoint(
+                        CAST(:lon AS double precision),
+                        CAST(:lat AS double precision)
+                    ),
+                    4326
+                )::geography
+            )
+            LIMIT 1
+            """
+        ),
+        {"lat": lat, "lon": lon, "radius": float(radius_m)},
+    ).first()
+
+    if row is None:
+        raise HTTPException(status_code=404, detail="no cadastral building found within radius")
+
+    return CadastralReverseResult(
+        address=row.readable_address,
+        lat=float(row.lat),
+        lon=float(row.lon),
+        distance_m=round(float(row.distance_m), 1),
+        cad_num=row.cad_num,
+    )
diff --git a/backend/app/main.py b/backend/app/main.py
index 07071a70..bd7afc5b 100644
--- a/backend/app/main.py
+++ b/backend/app/main.py
@@ -21,6 +21,7 @@ from app.api.v1 import (
     admin_scrape,
     admin_weight_profiles,
     analytics,
+    cadastral,
     concepts,
     custom_pois,
     landing,
@@ -78,6 +79,7 @@ app.add_middleware(
     allow_headers=["*"],
 )
 
+app.include_router(cadastral.router, prefix="/api/v1/cadastral", tags=["cadastral"])
 app.include_router(concepts.router, prefix="/api/v1/concepts", tags=["concepts"])
 app.include_router(parcels.router, prefix="/api/v1/parcels", tags=["parcels"])
 app.include_router(analytics.router, prefix="/api/v1/analytics", tags=["analytics"])
diff --git a/docker-compose.prod.yml b/docker-compose.prod.yml
index 8c77d93c..c121a217 100644
--- a/docker-compose.prod.yml
+++ b/docker-compose.prod.yml
@@ -67,6 +67,11 @@ services:
       timeout: 5s
       retries: 5
       start_period: 20s
+    networks:
+      default: {}
+      shared:
+        aliases:
+          - gendesign-backend
 
   frontend:
     image: ghcr.io/lekss361/gendesign-frontend:${IMAGE_TAG:-latest}
diff --git a/tradein-mvp/backend/app/core/config.py b/tradein-mvp/backend/app/core/config.py
index 167a9370..f3d7bf6f 100644
--- a/tradein-mvp/backend/app/core/config.py
+++ b/tradein-mvp/backend/app/core/config.py
@@ -32,5 +32,10 @@ class Settings(BaseSettings):
     # Redis URL для hot-cache (Phase 3.2). Задаётся через env REDIS_URL.
     redis_url: str = "redis://localhost:6379/0"
 
+    # Main GenDesign backend URL — для cadastral reverse geocode (cad_buildings).
+    # В prod: http://gendesign-backend:8000 (network alias в docker-compose.prod.yml).
+    # Пусто = cadastral lookup пропускается, используется только Nominatim.
+    main_backend_url: str | None = None
+
 
 settings = Settings()
diff --git a/tradein-mvp/backend/app/services/geocoder.py b/tradein-mvp/backend/app/services/geocoder.py
index d5f0e146..bc8c7982 100644
--- a/tradein-mvp/backend/app/services/geocoder.py
+++ b/tradein-mvp/backend/app/services/geocoder.py
@@ -569,14 +569,32 @@ def _format_reverse_address(addr: dict) -> str | None:
     return ", ".join(parts)
 
 
-@retry(stop=stop_after_attempt(3), wait=wait_exponential(multiplier=1, min=1, max=8))
-async def reverse_geocode(lat: float, lon: float) -> str | None:
-    """Обратный геокодинг: координаты → адрес (Nominatim /reverse).
+async def _cadastral_reverse(lat: float, lon: float) -> str | None:
+    """Reverse via main backend cad_buildings — fast, no external API.
 
-    Клик по дому на карте ЕКБ → адрес подставляется в форму оценки.
-    Возвращаем уличный адрес (улица, дом, город), а не `display_name` —
-    тот начинается с названия POI/организации и не геокодируется обратно.
+    Returns None on any error (network, 404, timeout, missing config).
     """
+    if not settings.main_backend_url:
+        return None
+    url = settings.main_backend_url.rstrip("/") + "/api/v1/cadastral/reverse"
+    try:
+        async with httpx.AsyncClient(timeout=3.0) as client:
+            response = await client.get(url, params={"lat": str(lat), "lon": str(lon)})
+        if response.status_code == 404:
+            return None
+        response.raise_for_status()
+        data = response.json()
+        addr = data.get("address")
+        if isinstance(addr, str) and addr.strip():
+            return addr
+    except Exception:
+        logger.exception("cadastral reverse failed for (%.5f, %.5f)", lat, lon)
+    return None
+
+
+@retry(stop=stop_after_attempt(3), wait=wait_exponential(multiplier=1, min=1, max=8))
+async def _nominatim_reverse(lat: float, lon: float) -> str | None:
+    """Nominatim /reverse — extracted for fallback usage. @retry handles transient errors."""
     headers = {
         "User-Agent": f"TradeInMVP/0.1 (contact: {settings.contact_email})",
         "Accept": "application/json",
@@ -603,3 +621,23 @@ async def reverse_geocode(lat: float, lon: float) -> str | None:
         if street:
             return street
     return data.get("display_name")
+
+
+async def reverse_geocode(lat: float, lon: float) -> str | None:
+    """Cadastral (cad_buildings via main backend) → Nominatim fallback.
+
+    Возвращает None если ни один источник не дал адрес. Endpoint
+    api/v1/geocode/reverse сам выкинет 404. НЕ даёт выйти HTTPStatusError
+    наверх — раньше Nominatim 403 → RetryError → FastAPI 500.
+    """
+    # 1. Cadastral primary (fast, no external API, returns жилой дом not POI)
+    cadastral = await _cadastral_reverse(lat, lon)
+    if cadastral:
+        return cadastral
+
+    # 2. Nominatim fallback (wrap to prevent 500 on ban/rate-limit)
+    try:
+        return await _nominatim_reverse(lat, lon)
+    except Exception:
+        logger.exception("nominatim reverse failed for (%.5f, %.5f)", lat, lon)
+        return None
diff --git a/tradein-mvp/backend/tests/services/__init__.py b/tradein-mvp/backend/tests/services/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/tradein-mvp/backend/tests/services/test_cadastral_reverse.py b/tradein-mvp/backend/tests/services/test_cadastral_reverse.py
new file mode 100644
index 00000000..d5585432
--- /dev/null
+++ b/tradein-mvp/backend/tests/services/test_cadastral_reverse.py
@@ -0,0 +1,150 @@
+"""Unit tests for cadastral reverse geocode and modified reverse_geocode."""
+from __future__ import annotations
+
+import os
+import sys
+from unittest.mock import AsyncMock, MagicMock, patch
+
+# DATABASE_URL required by config before any app import.
+os.environ.setdefault("DATABASE_URL", "postgresql+psycopg://test:test@localhost:5432/test")
+os.environ.setdefault("MAIN_BACKEND_URL", "http://gendesign-backend:8000")
+
+# WeasyPrint stub — not installed in CI without GTK.
+_wp_mock = MagicMock()
+sys.modules.setdefault("weasyprint", _wp_mock)
+
+import pytest
+
+from app.services.geocoder import _cadastral_reverse, reverse_geocode
+
+
+# ── _cadastral_reverse ────────────────────────────────────────────────────────
+
+
+async def test_cadastral_reverse_returns_address_on_200() -> None:
+    """Main backend returns 200 → address string returned."""
+    mock_response = MagicMock()
+    mock_response.status_code = 200
+    mock_response.raise_for_status = MagicMock()
+    mock_response.json.return_value = {
+        "address": "ул. Малышева, 30, Екатеринбург",
+        "lat": 56.838,
+        "lon": 60.605,
+        "distance_m": 12.5,
+    }
+
+    mock_client = AsyncMock()
+    mock_client.get = AsyncMock(return_value=mock_response)
+    mock_client.__aenter__ = AsyncMock(return_value=mock_client)
+    mock_client.__aexit__ = AsyncMock(return_value=False)
+
+    with patch("app.services.geocoder.httpx.AsyncClient", return_value=mock_client):
+        result = await _cadastral_reverse(56.838, 60.605)
+
+    assert result == "ул. Малышева, 30, Екатеринбург"
+
+
+async def test_cadastral_reverse_returns_none_on_404() -> None:
+    """Main backend returns 404 (no building in radius) → None, no exception."""
+    mock_response = MagicMock()
+    mock_response.status_code = 404
+
+    mock_client = AsyncMock()
+    mock_client.get = AsyncMock(return_value=mock_response)
+    mock_client.__aenter__ = AsyncMock(return_value=mock_client)
+    mock_client.__aexit__ = AsyncMock(return_value=False)
+
+    with patch("app.services.geocoder.httpx.AsyncClient", return_value=mock_client):
+        result = await _cadastral_reverse(56.838, 60.605)
+
+    assert result is None
+
+
+async def test_cadastral_reverse_returns_none_on_timeout() -> None:
+    """Network timeout → None returned, no exception bubbles out."""
+    import httpx
+
+    mock_client = AsyncMock()
+    mock_client.get = AsyncMock(side_effect=httpx.TimeoutException("timeout"))
+    mock_client.__aenter__ = AsyncMock(return_value=mock_client)
+    mock_client.__aexit__ = AsyncMock(return_value=False)
+
+    with patch("app.services.geocoder.httpx.AsyncClient", return_value=mock_client):
+        result = await _cadastral_reverse(56.838, 60.605)
+
+    assert result is None
+
+
+async def test_cadastral_reverse_returns_none_when_not_configured() -> None:
+    """main_backend_url is None → immediately returns None without HTTP call."""
+    with patch("app.services.geocoder.settings") as mock_settings:
+        mock_settings.main_backend_url = None
+
+        with patch("app.services.geocoder.httpx.AsyncClient") as mock_client_cls:
+            result = await _cadastral_reverse(56.838, 60.605)
+            mock_client_cls.assert_not_called()
+
+    assert result is None
+
+
+# ── reverse_geocode ───────────────────────────────────────────────────────────
+
+
+async def test_reverse_geocode_returns_cadastral_when_available() -> None:
+    """Cadastral returns address → Nominatim is never called."""
+    with (
+        patch(
+            "app.services.geocoder._cadastral_reverse",
+            new_callable=AsyncMock,
+            return_value="ул. Малышева, 30, Екатеринбург",
+        ) as mock_cadastral,
+        patch(
+            "app.services.geocoder._nominatim_reverse",
+            new_callable=AsyncMock,
+        ) as mock_nominatim,
+    ):
+        result = await reverse_geocode(56.838, 60.605)
+
+    assert result == "ул. Малышева, 30, Екатеринбург"
+    mock_cadastral.assert_called_once_with(56.838, 60.605)
+    mock_nominatim.assert_not_called()
+
+
+async def test_reverse_geocode_falls_back_to_nominatim_when_cadastral_none() -> None:
+    """Cadastral returns None → Nominatim is called and its result returned."""
+    with (
+        patch(
+            "app.services.geocoder._cadastral_reverse",
+            new_callable=AsyncMock,
+            return_value=None,
+        ),
+        patch(
+            "app.services.geocoder._nominatim_reverse",
+            new_callable=AsyncMock,
+            return_value="Трамвайный переулок, 2, Екатеринбург",
+        ) as mock_nominatim,
+    ):
+        result = await reverse_geocode(56.838, 60.605)
+
+    assert result == "Трамвайный переулок, 2, Екатеринбург"
+    mock_nominatim.assert_called_once_with(56.838, 60.605)
+
+
+async def test_reverse_geocode_returns_none_when_both_fail() -> None:
+    """Both cadastral and Nominatim fail → returns None, no exception raised."""
+    with (
+        patch(
+            "app.services.geocoder._cadastral_reverse",
+            new_callable=AsyncMock,
+            return_value=None,
+        ),
+        patch(
+            "app.services.geocoder._nominatim_reverse",
+            new_callable=AsyncMock,
+            side_effect=RuntimeError("Nominatim 403 Forbidden — IP banned"),
+        ),
+    ):
+        result = await reverse_geocode(56.838, 60.605)
+
+    # Must return None, not raise
+    assert result is None
diff --git a/tradein-mvp/docker-compose.prod.yml b/tradein-mvp/docker-compose.prod.yml
index 83400ba1..f1b55f33 100644
--- a/tradein-mvp/docker-compose.prod.yml
+++ b/tradein-mvp/docker-compose.prod.yml
@@ -45,6 +45,7 @@ services:
       ADMIN_TOKEN: "${ADMIN_TOKEN:-}"
       # GlitchTip DSN — мониторинг ошибок (#396). Пусто = выключено.
       GLITCHTIP_DSN: "${GLITCHTIP_DSN:-}"
+      MAIN_BACKEND_URL: "${MAIN_BACKEND_URL:-http://gendesign-backend:8000}"
     depends_on:
       postgres:
         condition: service_healthy