fix: type the ids filter from its configured id type

advanced_alchemy annotates the `ids` query parameter as list[str] whatever the
config says, so a bigint primary key was compared against strings and Postgres
refused. Nothing had called ?ids= until now.

backend/src/chitai/services/dependencies.py

@@ -127,6 +127,31 @@ def create_book_filter_dependencies(
     # Get base filters first
     filters = create_filter_dependencies(config, dep_defaults)
 
+    # OVERRIDE: id filter typed by the configured id type, not always `str`
+    #
+    # advanced_alchemy's `provide_id_filter` annotates `ids` as `list[str]` and
+    # ignores `config["id_filter"]` entirely, so `?ids=12` reaches the database as
+    # the string "12" and Postgres refuses `bigint = character varying`. Nothing
+    # called `?ids=` until the duplicates screen needed to fetch a handful of books
+    # by id, which is why it went unnoticed.
+    if id_type := config.get("id_filter"):
+        id_field = config.get("id_field", "id")
+
+        def provide_typed_id_filter(
+            ids=Parameter(query="ids", default=None, required=False),
+        ) -> CollectionFilter:
+            return CollectionFilter(field_name=id_field, values=ids)
+
+        # Attached as a type object rather than written as an annotation: this module
+        # has `from __future__ import annotations`, so a written one is stored as the
+        # string "Optional[list[id_type]]" and resolved against module globals, where
+        # a local named `id_type` does not exist.
+        provide_typed_id_filter.__annotations__["ids"] = Optional[list[id_type]]
+
+        filters[dep_defaults.ID_FILTER_DEPENDENCY_KEY] = Provide(
+            provide_typed_id_filter, sync_to_thread=False
+        )
+
     # OVERRIDE: Custom search filter with trigram search
     if config.get("search"):
         search_fields = config.get("search")

backend/tests/integration/test_book.py

@@ -209,6 +209,21 @@ async def test_get_book_file(
     assert downloaded_content == file_content
 
 
+async def test_list_books_by_id(populated_authenticated_client: AsyncClient) -> None:
+    """
+    `?ids=` has to reach the database as integers.
+
+    advanced_alchemy's stock id filter annotates the parameter as `list[str]` whatever
+    the configured id type, so the ids arrived as strings and Postgres refused to
+    compare a bigint primary key against them. Nothing called it until a screen needed
+    to fetch a handful of books by id.
+    """
+    response = await populated_authenticated_client.get("/books?ids=1&ids=2&pageSize=10")
+
+    assert response.status_code == 200
+    assert sorted(book["id"] for book in response.json()["items"]) == [1, 2]
+
+
 async def test_get_book_by_id(populated_authenticated_client: AsyncClient) -> None:
     """Test retrieving a specific book by ID."""