Add list_marketplaces to MarketService protocol, impl, and stub

Paginated query for market listings — supports optional container filtering
and returns (dtos, has_more) for infinite scroll.

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

services/market_impl.py

@@ -52,6 +52,23 @@ class SqlMarketService:
         )
         return [_mp_to_dto(mp) for mp in result.scalars().all()]
 
+    async def list_marketplaces(
+        self, session: AsyncSession,
+        container_type: str | None = None, container_id: int | None = None,
+        *, page: int = 1, per_page: int = 20,
+    ) -> tuple[list[MarketPlaceDTO], bool]:
+        stmt = select(MarketPlace).where(MarketPlace.deleted_at.is_(None))
+        if container_type is not None and container_id is not None:
+            stmt = stmt.where(
+                MarketPlace.container_type == container_type,
+                MarketPlace.container_id == container_id,
+            )
+        stmt = stmt.order_by(MarketPlace.name.asc())
+        stmt = stmt.offset((page - 1) * per_page).limit(per_page + 1)
+        rows = (await session.execute(stmt)).scalars().all()
+        has_more = len(rows) > per_page
+        return [_mp_to_dto(mp) for mp in rows[:per_page]], has_more
+
     async def product_by_id(self, session: AsyncSession, product_id: int) -> ProductDTO | None:
         product = (
             await session.execute(select(Product).where(Product.id == product_id))

services/stubs.py

@@ -156,6 +156,13 @@ class StubMarketService:
     ) -> list[MarketPlaceDTO]:
         return []
 
+    async def list_marketplaces(
+        self, session: AsyncSession,
+        container_type: str | None = None, container_id: int | None = None,
+        *, page: int = 1, per_page: int = 20,
+    ) -> tuple[list[MarketPlaceDTO], bool]:
+        return [], False
+
     async def product_by_id(self, session: AsyncSession, product_id: int) -> ProductDTO | None:
         return None