add sandbox network auto-create and restore dind compose

adapter/http/fastapi/app.py

@@ -1,6 +1,7 @@
 import asyncio
 from collections.abc import Awaitable, Callable
 
+from docker.errors import NotFound
 from fastapi import FastAPI
 from opentelemetry.instrumentation.fastapi import FastAPIInstrumentor
 
@@ -47,6 +48,19 @@ def create_app(config: AppConfig | None = None) -> FastAPI:
         raise
 
 
+def _ensure_sandbox_network(container: AppContainer) -> None:
+    client = container._docker_client
+    network_name = container.config.sandbox.network_name
+    try:
+        client.networks.get(network_name)
+    except NotFound:
+        client.networks.create(network_name)
+        container.observability.logger.info(
+            'sandbox_network_created',
+            attrs={'network': network_name},
+        )
+
+
 def _build_startup_handler(
     app: FastAPI,
     container: AppContainer,
@@ -56,6 +70,7 @@ def _build_startup_handler(
         if task is not None and not task.done():
             return
 
+        await asyncio.to_thread(_ensure_sandbox_network, container)
         await asyncio.to_thread(container.sandbox_reconciler.execute)
 
         stop_event = asyncio.Event()