refactor(api): extract workspace list into layered application service (#39822)

Co-authored-by: WH-2099 <wh2099@pm.me>

api/extensions/ext_application_services.py

@@ -0,0 +1,44 @@
+"""Composition root for application services used by transport adapters."""
+
+from dataclasses import dataclass
+from typing import cast
+
+from flask import Flask, current_app
+from sqlalchemy.orm import Session, sessionmaker
+
+from core.db.session_factory import get_session_maker
+from repositories.workspace_query_repository import WorkspaceQueryRepository
+from services.workspace_query_compat import LegacyWorkspacePlanGateway
+from services.workspace_query_service import WorkspaceQueryService
+
+_EXTENSION_KEY = "application_services"
+
+
+@dataclass(frozen=True, slots=True)
+class ApplicationServices:
+    workspace_queries: WorkspaceQueryService
+
+
+def build_application_services(
+    *,
+    database_client: sessionmaker[Session],
+) -> ApplicationServices:
+    return ApplicationServices(
+        workspace_queries=WorkspaceQueryService(
+            workspaces=WorkspaceQueryRepository(
+                client=database_client,
+            ),
+            plans=LegacyWorkspacePlanGateway(),
+        )
+    )
+
+
+def init_app(app: Flask) -> None:
+    app.extensions[_EXTENSION_KEY] = build_application_services(
+        database_client=get_session_maker(),
+    )
+
+
+def application_services() -> ApplicationServices:
+    """Return the application services bound to the current Flask app."""
+    return cast(ApplicationServices, current_app.extensions[_EXTENSION_KEY])