chore(docker): Refactor sandbox state management and improve Docker integration (#1068)

* Refactor sandbox state management and improve Docker integration

- Removed FileSandboxStateStore and SandboxStateStore classes for a cleaner architecture.
- Enhanced LocalContainerBackend to handle port allocation retries and introduced environment variable support for sandbox host configuration.
- Updated Paths class to include host_base_dir for Docker volume mounts and ensured proper permissions for sandbox directories.
- Modified ExtensionsConfig to improve error handling when loading configuration files and adjusted environment variable resolution.
- Updated sandbox configuration to include a replicas option for managing concurrent sandbox containers.
- Improved logging and context management in SandboxMiddleware for better sandbox lifecycle handling.
- Enhanced network port allocation logic to bind to 0.0.0.0 for compatibility with Docker.
- Updated Docker Compose files to ensure proper volume management and environment variable configuration.
- Created scripts to ensure necessary configuration files are present before starting services.
- Cleaned up unused MCP server configurations in extensions_config.example.json.

* Address Copilot review suggestions from PR #1068 (#9)

---------

Co-authored-by: Copilot <198982749+Copilot@users.noreply.github.com>

backend/src/sandbox/middleware.py

@@ -1,3 +1,4 @@
+import logging
 from typing import NotRequired, override
 
 from langchain.agents import AgentState
@@ -7,6 +8,8 @@ from langgraph.runtime import Runtime
 from src.agents.thread_state import SandboxState, ThreadDataState
 from src.sandbox import get_sandbox_provider
 
+logger = logging.getLogger(__name__)
+
 
 class SandboxMiddlewareState(AgentState):
     """Compatible with the `ThreadState` schema."""
@@ -42,7 +45,7 @@ class SandboxMiddleware(AgentMiddleware[SandboxMiddlewareState]):
     def _acquire_sandbox(self, thread_id: str) -> str:
         provider = get_sandbox_provider()
         sandbox_id = provider.acquire(thread_id)
-        print(f"Acquiring sandbox {sandbox_id}")
+        logger.info(f"Acquiring sandbox {sandbox_id}")
         return sandbox_id
 
     @override
@@ -54,7 +57,25 @@ class SandboxMiddleware(AgentMiddleware[SandboxMiddlewareState]):
         # Eager initialization (original behavior)
         if "sandbox" not in state or state["sandbox"] is None:
             thread_id = runtime.context["thread_id"]
-            print(f"Thread ID: {thread_id}")
             sandbox_id = self._acquire_sandbox(thread_id)
+            logger.info(f"Assigned sandbox {sandbox_id} to thread {thread_id}")
             return {"sandbox": {"sandbox_id": sandbox_id}}
         return super().before_agent(state, runtime)
+
+    @override
+    def after_agent(self, state: SandboxMiddlewareState, runtime: Runtime) -> dict | None:
+        sandbox = state.get("sandbox")
+        if sandbox is not None:
+            sandbox_id = sandbox["sandbox_id"]
+            logger.info(f"Releasing sandbox {sandbox_id}")
+            get_sandbox_provider().release(sandbox_id)
+            return None
+
+        if runtime.context.get("sandbox_id") is not None:
+            sandbox_id = runtime.context.get("sandbox_id")
+            logger.info(f"Releasing sandbox {sandbox_id} from context")
+            get_sandbox_provider().release(sandbox_id)
+            return None
+
+        # No sandbox to release
+        return super().after_agent(state, runtime)