feat(BA-5829): add AppConfigFragment DataLoader for N+1 batching

Follows the `audit_log_loader` / `prometheus_query_preset_category_loader`
pattern — adapter exposes `batch_load_by_ids(ids)` which goes through
the `SearchAppConfigFragments` action path with an id-filter condition,
and `DataLoaders.app_config_fragment_loader` wraps it for use from
GQL resolvers via `info.context.data_loaders.app_config_fragment_loader`.

Cross-scope `admin_search` is used instead of the scope-bound `search`
action because DataLoader batches span scopes; authorization is already
enforced at the parent resolver before the loader is ever invoked
(same stance as other loaders in the registry).

Adds:
- `AppConfigFragmentAdapter.batch_load_by_ids` (adapter-level batching
  via `AppConfigFragmentConditions.by_ids` + `OffsetPagination(len(ids))`).
- `DataLoaders.app_config_fragment_loader` cached-property.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: jopemachine

src/ai/backend/manager/api/adapters/app_config_fragment.py

@@ -2,6 +2,9 @@
 
 from __future__ import annotations
 
+import uuid
+from collections.abc import Sequence
+
 from ai.backend.common.dto.manager.v2.app_config_fragment.request import (
     AppConfigFragmentFilter,
     AppConfigFragmentKeyInput,
@@ -35,7 +38,12 @@
 from ai.backend.manager.repositories.app_config_fragment.types import (
     AppConfigFragmentSearchScope,
 )
-from ai.backend.manager.repositories.base import BatchQuerier, QueryCondition, QueryOrder
+from ai.backend.manager.repositories.base import (
+    BatchQuerier,
+    OffsetPagination,
+    QueryCondition,
+    QueryOrder,
+)
 from ai.backend.manager.services.app_config_fragment.actions.admin_search import (
     AdminSearchAppConfigFragmentsAction,
 )
@@ -60,6 +68,31 @@
 class AppConfigFragmentAdapter(BaseAdapter):
     """Adapter for AppConfigFragment domain operations (BEP-1052 §2)."""
 
+    async def batch_load_by_ids(
+        self, ids: Sequence[uuid.UUID]
+    ) -> list[AppConfigFragmentNode | None]:
+        """Batch-load fragments by id for DataLoader use.
+
+        Returns `AppConfigFragmentNode` DTOs in the same order as the
+        input `ids`, with `None` placeholders for rows that do not
+        exist (Relay batching contract). Goes through the cross-scope
+        search action because the scope-bound variant requires a single
+        `(scope_type, scope_id)` slice — DataLoader batches span
+        scopes. Authorization for the overall query is enforced at the
+        parent resolver before this loader is invoked.
+        """
+        if not ids:
+            return []
+        querier = BatchQuerier(
+            pagination=OffsetPagination(limit=len(ids)),
+            conditions=[AppConfigFragmentConditions.by_ids(ids)],
+        )
+        result = await self._processors.app_config_fragment.admin_search.wait_for_complete(
+            AdminSearchAppConfigFragmentsAction(querier=querier)
+        )
+        by_id = {item.id: self._data_to_dto(item) for item in result.items}
+        return [by_id.get(fragment_id) for fragment_id in ids]
+
     async def create(self, input: CreateAppConfigFragmentInput) -> CreateAppConfigFragmentPayload:
         key = self._input_to_key(input.key)
         result = await self._processors.app_config_fragment.create.wait_for_complete(

src/ai/backend/manager/api/gql/data_loader/data_loaders.py

@@ -13,6 +13,9 @@
     from ai.backend.common.dto.manager.v2.rbac.response import EntityNode  # pants: no-infer-dep
     from ai.backend.manager.api.adapters.registry import Adapters  # pants: no-infer-dep
     from ai.backend.manager.api.gql.agent.types import AgentV2GQL  # pants: no-infer-dep
+    from ai.backend.manager.api.gql.app_config_fragment.types import (  # pants: no-infer-dep
+        AppConfigFragmentGQL,
+    )
     from ai.backend.manager.api.gql.artifact.types import (  # pants: no-infer-dep
         ArtifactRevision,
     )
@@ -112,6 +115,22 @@ class DataLoaders:
     def __init__(self, adapters: Adapters) -> None:
         self._adapters = adapters
 
+    @cached_property
+    def app_config_fragment_loader(
+        self,
+    ) -> DataLoader[uuid.UUID, AppConfigFragmentGQL | None]:
+        adapter = self._adapters.app_config_fragment
+
+        async def load_fn(ids: list[uuid.UUID]) -> list[AppConfigFragmentGQL | None]:
+            from ai.backend.manager.api.gql.app_config_fragment.types import (  # pants: no-infer-dep
+                AppConfigFragmentGQL as F,
+            )
+
+            dtos = await adapter.batch_load_by_ids(ids)
+            return [F.from_pydantic(dto) if dto is not None else None for dto in dtos]
+
+        return DataLoader(load_fn=load_fn)
+
     @cached_property
     def audit_log_loader(
         self,