feat(services): add station_service with CRUD and assignment logic

Implements create/update/delete station, assign/unassign recipe,
list_station_recipes (active only, ordered by code), and get_station_by_code.
Explicit ORM-level assignment deletion in delete_station ensures cascade
works engine-agnostically (SQLite tests + MySQL production). 10 TDD tests.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/tests/test_station_service.py

@@ -0,0 +1,114 @@
+"""Tests for station_service business logic."""
+import pytest
+from fastapi import HTTPException
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from models.station import Station
+from schemas.station import StationCreate, StationUpdate
+from services.station_service import (
+    create_station, update_station, delete_station,
+    assign_recipe, unassign_recipe, list_station_recipes,
+    get_station_by_code,
+)
+from tests.conftest import _create_user, create_test_recipe
+
+
+async def test_create_station_ok(db_session: AsyncSession):
+    admin = await _create_user(db_session, username="a1", is_admin=True)
+    station = await create_station(
+        db_session, StationCreate(code="ST-100", name="Pilot"), admin
+    )
+    assert station.id is not None
+    assert station.code == "ST-100"
+
+
+async def test_create_station_duplicate_code(db_session: AsyncSession):
+    admin = await _create_user(db_session, username="a2", is_admin=True)
+    await create_station(db_session, StationCreate(code="ST-DUP", name="A"), admin)
+    with pytest.raises(HTTPException) as exc:
+        await create_station(db_session, StationCreate(code="ST-DUP", name="B"), admin)
+    assert exc.value.status_code == 409
+
+
+async def test_update_station(db_session: AsyncSession):
+    admin = await _create_user(db_session, username="a3", is_admin=True)
+    station = await create_station(db_session, StationCreate(code="ST-U", name="Old"), admin)
+    updated = await update_station(
+        db_session, station.id, StationUpdate(name="New name"),
+    )
+    assert updated.name == "New name"
+    assert updated.code == "ST-U"
+
+
+async def test_update_missing_station(db_session: AsyncSession):
+    with pytest.raises(HTTPException) as exc:
+        await update_station(db_session, 9999, StationUpdate(name="x"))
+    assert exc.value.status_code == 404
+
+
+async def test_assign_and_list_recipes(db_session: AsyncSession):
+    admin = await _create_user(db_session, username="a4", is_admin=True)
+    station = await create_station(db_session, StationCreate(code="ST-R", name="R"), admin)
+    r1 = await create_test_recipe(db_session, user_id=admin.id, code="REC-R1")
+    r2 = await create_test_recipe(db_session, user_id=admin.id, code="REC-R2")
+    await assign_recipe(db_session, station.id, r1.id, admin)
+    await assign_recipe(db_session, station.id, r2.id, admin)
+    recipes = await list_station_recipes(db_session, station.id)
+    assert {r.code for r in recipes} == {"REC-R1", "REC-R2"}
+
+
+async def test_assign_same_recipe_twice_is_409(db_session: AsyncSession):
+    admin = await _create_user(db_session, username="a5", is_admin=True)
+    station = await create_station(db_session, StationCreate(code="ST-D", name="D"), admin)
+    r = await create_test_recipe(db_session, user_id=admin.id, code="REC-D")
+    await assign_recipe(db_session, station.id, r.id, admin)
+    with pytest.raises(HTTPException) as exc:
+        await assign_recipe(db_session, station.id, r.id, admin)
+    assert exc.value.status_code == 409
+
+
+async def test_unassign_recipe(db_session: AsyncSession):
+    admin = await _create_user(db_session, username="a6", is_admin=True)
+    station = await create_station(db_session, StationCreate(code="ST-UN", name="UN"), admin)
+    r = await create_test_recipe(db_session, user_id=admin.id, code="REC-UN")
+    await assign_recipe(db_session, station.id, r.id, admin)
+    await unassign_recipe(db_session, station.id, r.id)
+    recipes = await list_station_recipes(db_session, station.id)
+    assert recipes == []
+
+
+async def test_get_station_by_code(db_session: AsyncSession):
+    admin = await _create_user(db_session, username="a7", is_admin=True)
+    await create_station(db_session, StationCreate(code="ST-FIND", name="F"), admin)
+    found = await get_station_by_code(db_session, "ST-FIND")
+    assert found is not None
+    assert found.name == "F"
+    missing = await get_station_by_code(db_session, "ST-NOPE")
+    assert missing is None
+
+
+async def test_list_recipes_only_returns_active(db_session: AsyncSession):
+    admin = await _create_user(db_session, username="a8", is_admin=True)
+    station = await create_station(db_session, StationCreate(code="ST-A", name="A"), admin)
+    active = await create_test_recipe(db_session, user_id=admin.id, code="REC-AC")
+    inactive = await create_test_recipe(db_session, user_id=admin.id, code="REC-IN")
+    inactive.active = False
+    await db_session.flush()
+    await assign_recipe(db_session, station.id, active.id, admin)
+    await assign_recipe(db_session, station.id, inactive.id, admin)
+    recipes = await list_station_recipes(db_session, station.id)
+    assert [r.code for r in recipes] == ["REC-AC"]
+
+
+async def test_delete_station_cascades_assignments(db_session: AsyncSession):
+    from sqlalchemy import select
+    from models.station import StationRecipeAssignment
+    admin = await _create_user(db_session, username="a9", is_admin=True)
+    station = await create_station(db_session, StationCreate(code="ST-DEL", name="D"), admin)
+    r = await create_test_recipe(db_session, user_id=admin.id, code="REC-DEL")
+    await assign_recipe(db_session, station.id, r.id, admin)
+    await delete_station(db_session, station.id)
+    remaining = await db_session.execute(
+        select(StationRecipeAssignment).where(StationRecipeAssignment.station_id == station.id)
+    )
+    assert remaining.scalars().all() == []