backend/src/sandbox/middleware.py

from typing import NotRequired, override

from langchain.agents import AgentState
from langchain.agents.middleware import AgentMiddleware
from langgraph.runtime import Runtime

from src.agents.thread_state import SandboxState, ThreadDataState
from src.sandbox import get_sandbox_provider
from src.utils.runtime import get_runtime_thread_id


class SandboxMiddlewareState(AgentState):
    """Compatible with the `ThreadState` schema."""

    sandbox: NotRequired[SandboxState | None]
    thread_data: NotRequired[ThreadDataState | None]


class SandboxMiddleware(AgentMiddleware[SandboxMiddlewareState]):
    """Create a sandbox environment and assign it to an agent.

    Lifecycle Management:
    - With lazy_init=True (default): Sandbox is acquired on first tool call
    - With lazy_init=False: Sandbox is acquired on first agent invocation (before_agent)
    - Sandbox is reused across multiple turns within the same thread
    - Sandbox is NOT released after each agent call to avoid wasteful recreation
    - Cleanup happens at application shutdown via SandboxProvider.shutdown()
    """

    state_schema = SandboxMiddlewareState

    def __init__(self, lazy_init: bool = True):
        """Initialize sandbox middleware.

        Args:
            lazy_init: If True, defer sandbox acquisition until first tool call.
                      If False, acquire sandbox eagerly in before_agent().
                      Default is True for optimal performance.
        """
        super().__init__()
        self._lazy_init = lazy_init

    def _acquire_sandbox(self, thread_id: str) -> str:
        provider = get_sandbox_provider()
        sandbox_id = provider.acquire(thread_id)
        print(f"Acquiring sandbox {sandbox_id}")
        return sandbox_id

    @override
    def before_agent(self, state: SandboxMiddlewareState, runtime: Runtime) -> dict | None:
        # Skip acquisition if lazy_init is enabled
        if self._lazy_init:
            return super().before_agent(state, runtime)

        # Eager initialization (original behavior)
        if "sandbox" not in state or state["sandbox"] is None:
            thread_id = get_runtime_thread_id(runtime)
            if thread_id is None:
                raise ValueError("Thread ID is required in runtime context or metadata")
            print(f"Thread ID: {thread_id}")
            sandbox_id = self._acquire_sandbox(thread_id)
            return {"sandbox": {"sandbox_id": sandbox_id}}
        return super().before_agent(state, runtime)