perf(api): хелпер ответа из готовых JSON-строк и SQL-выражение строки

Добавлены list_json_response (обёртка BaseListResponse из готовых строк),
ROW_COLUMNS, row_json_select и fetch_row_texts для тяжёлых GET (AURORA-1848).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

api/src/api/v1/json_response.py

@@ -0,0 +1,14 @@
+"""Ответ тяжёлых GET из готовых JSON-строк Postgres (AURORA-1848, design D3)."""
+from fastapi import Response
+
+
+def list_json_response(rows: list[str], headers: dict[str, str] | None = None) -> Response:
+    """Обёртка как у BaseListResponse при успехе; rows — уже сериализованные строки ответа."""
+    body = b"".join((
+        b'{"success":true,"message":null,"result":[',
+        ",".join(rows).encode(),
+        b'],"count":',
+        str(len(rows)).encode(),
+        b"}",
+    ))
+    return Response(content=body, media_type="application/json", headers=headers)

api/src/repository/row_json.py

@@ -0,0 +1,17 @@
+"""Строка ответа тяжёлого GET как текст JSON из Postgres (AURORA-1848, design D1)."""
+from sqlalchemy import text
+from sqlalchemy.ext.asyncio import AsyncSession
+
+ROW_COLUMNS = "row_type, depth, sort_order, data"
+
+
+def row_json_select(row_type: str = "row_type", depth: str = "depth") -> str:
+    """json (не jsonb) сохраняет порядок ключей; ::text обходит кодек json.loads у asyncpg."""
+    return (
+        f"SELECT json_build_object('row_type', {row_type}, 'depth', {depth}, "
+        f"'data', data, 'sort_order', sort_order)::text"
+    )
+
+
+async def fetch_row_texts(db: AsyncSession, sql: str, params: dict) -> list[str]:
+    return list((await db.execute(text(sql), params)).scalars().all())

api/tests/unit/test_json_list_response.py

@@ -0,0 +1,41 @@
+import json
+
+from src.api.v1.json_response import list_json_response
+from src.repository.row_json import ROW_COLUMNS, row_json_select
+
+
+def test_list_json_response_empty():
+    r = list_json_response([])
+    assert json.loads(r.body) == {"success": True, "message": None, "result": [], "count": 0}
+
+
+def test_list_json_response_rows_order_count_escaping():
+    rows = [
+        '{"row_type":"META","depth":-1,"data":{"a":null},"sort_order":null}',
+        r'{"row_type": "INPUT", "depth": 3, "data": {"t": "Кавычка \" и \\ слэш\nперенос"}, "sort_order": 1}',
+    ]
+    body = json.loads(list_json_response(rows).body)
+    assert list(body) == ["success", "message", "result", "count"]
+    assert body["count"] == 2
+    assert [row["row_type"] for row in body["result"]] == ["META", "INPUT"]
+    assert body["result"][0]["data"] == {"a": None}
+    assert body["result"][1]["data"]["t"] == 'Кавычка " и \\ слэш\nперенос'
+
+
+def test_list_json_response_media_type_and_headers():
+    r = list_json_response(["{}"], headers={"X-DB-Time-Ms": "1.50"})
+    assert r.media_type == "application/json"
+    assert r.headers["content-type"] == "application/json"
+    assert r.headers["x-db-time-ms"] == "1.50"
+    assert r.headers["content-length"] == str(len(r.body))
+
+
+def test_row_json_select_key_order():
+    assert ROW_COLUMNS == "row_type, depth, sort_order, data"
+    assert row_json_select() == (
+        "SELECT json_build_object('row_type', row_type, 'depth', depth, "
+        "'data', data, 'sort_order', sort_order)::text"
+    )
+    assert row_json_select(row_type="'INPUT'::VARCHAR", depth="3").startswith(
+        "SELECT json_build_object('row_type', 'INPUT'::VARCHAR, 'depth', 3, "
+    )