Advanced: assemble a sandbox yourself

create_sandbox_session connects the SDK components into a familiar sandbox interface. ConTree executes from filesystem images; a long-lived, mutable VM is not its persistence model. The default LazySession provides continuity between commands, then saves files at a snapshot boundary. Use the factory for normal application code. Build the components directly when you need to control their construction, share them, or replace their behavior. These examples show the components behind the default sandbox and their cleanup order. Configure a connection as described in Connection sources and use an available image with sleep, a POSIX shell, and cat.

What the factory supplies

Component	Factory default	Your control
Connection	Resolve a Profile from explicit arguments, ENV, or INI.	Supply a Profile or an already configured client.
Client	HTTPX for sync; aiohttp for async.	Select a client class or manage the connection yourself.
Store	A memory Store for history and reusable uploads.	Supply SQLite or your own Store implementation.
File transfer	A cached client transfer for uploads and saved-image reads.	Customize the underlying transfer; reuse uses the same Store.
Base session	`ContreeSession` or `ContreeAsyncSession`.	Extend request preparation, commits, or operation creation.
Lazy session	Reuse one VM; snapshot after 10 idle seconds.	Select a policy or subclass the lazy session.
Cleanup	Finish the session, then close owned storage and the client.	Manage component lifetimes explicitly; borrowed objects remain yours.

The factory reuses uploads through the same Store, with cache_ttl=60 by default. See Reuse uploads and retain their sources for lifetime and connection-scope details.

Build the default components explicitly

Both programs write a file, read it in the same VM, and print Hello from ConTree!. Normal exit saves pending filesystem changes. An exception inside the lazy context discards changes since its last completed snapshot.

Sync
Async

"""Assemble a sandbox and run two commands."""

from contree_client import profiles
from contree_client.httpx import ContreeClient

from contree_sdk import ContreeSession, LazySession
from contree_sdk.files import ClientFileTransfer
from contree_sdk.session import IdleSnapshotPolicy
from contree_sdk.store import SyncMemoryStore
from contree_sdk.scope import StoreScope
from contree_sdk.upload_cache import CachedFileTransfer


def main() -> None:
    profile = profiles.from_env() or profiles.resolve_profile()
    with ContreeClient.from_profile(profile) as client:
        with SyncMemoryStore() as store:
            transfer = CachedFileTransfer(
                ClientFileTransfer(client), store, scope=StoreScope.from_client(client), ttl=60
            )
            base = ContreeSession(client, image="tag:alpine:latest", store=store, file_transfer=transfer)
            policy = IdleSnapshotPolicy(10)
            with LazySession(base, snapshot_policy=policy) as sandbox:
                sandbox.run(shell="echo 'Hello from ConTree!' > /message.txt")
                result = sandbox.run("cat", args=["/message.txt"])
                print(result.stdout.as_text(), end="")


main()

import asyncio

from contree_client import profiles
from contree_client.aiohttp import ContreeAsyncClient

from contree_sdk import AsyncLazySession, ContreeAsyncSession
from contree_sdk.files import AsyncClientFileTransfer
from contree_sdk.session import IdleSnapshotPolicy
from contree_sdk.store import AsyncMemoryStore
from contree_sdk.scope import StoreScope
from contree_sdk.upload_cache import AsyncCachedFileTransfer


async def main() -> None:
    profile = profiles.from_env() or profiles.resolve_profile()
    async with ContreeAsyncClient.from_profile(profile) as client:
        async with AsyncMemoryStore() as store:
            transfer = AsyncCachedFileTransfer(
                AsyncClientFileTransfer(client), store, scope=StoreScope.from_client(client), ttl=60
            )
            base = ContreeAsyncSession(client, image="tag:alpine:latest", store=store, file_transfer=transfer)
            await base.ensure_ready()
            policy = IdleSnapshotPolicy(10)
            async with AsyncLazySession(base, snapshot_policy=policy) as sandbox:
                await sandbox.run(shell="echo 'Hello from ConTree!' > /message.txt")
                result = await sandbox.run("cat", args=["/message.txt"])
                print(result.stdout.as_text(), end="")


asyncio.run(main())

ensure_ready() resolves the initial image and history; it does not start a VM. The first lazy command starts the VM. The lazy context exits before the store and client contexts, so saving can still use both components. These programs show ordinary component assembly. The factory also handles partial entry failures, preserves a body exception if cleanup fails, and joins async cleanup under repeated cancellation. Reuse its context implementation when those guarantees are needed in a custom factory; see Sandbox factories.

Change one component without rebuilding everything

The factory accepts the same extension points. This selects a custom base session that adds a default command timeout. Each command uses an independent operation.

Sync
Async

from dataclasses import replace

from contree_sdk import ContreeSession, RunRequest, create_sync_sandbox_session


class TimedSession(ContreeSession):
    def prepare_request(self, request: RunRequest) -> RunRequest:
        request = super().prepare_request(request)
        return replace(request, timeout=30 if request.timeout is None else request.timeout)


with create_sync_sandbox_session(image="tag:alpine:latest", session_type=TimedSession) as session:
    session.run("echo", args=["Custom request policy"])

from dataclasses import replace

from contree_sdk import ContreeAsyncSession, RunRequest, create_async_sandbox_session


class TimedAsyncSession(ContreeAsyncSession):
    def prepare_request(self, request: RunRequest) -> RunRequest:
        request = super().prepare_request(request)
        return replace(request, timeout=30 if request.timeout is None else request.timeout)


async with create_async_sandbox_session(image="tag:alpine:latest", session_type=TimedAsyncSession) as session:
    await session.run("echo", args=["Custom request policy"])

Selecting ContreeSession or ContreeAsyncSession saves each command by default in a separate VM. Use disposable=True to leave the session image unchanged. Selecting a lazy subclass retains a shared VM until a snapshot. Snapshots are lightweight and can run after every command, but they stop the VM. An unchanged filesystem can produce the same image UUID. session_kwargs configures the selected class; store, file_transfer, and commit_policy configure its underlying base session. To supply a custom base session inside a lazy wrapper, assemble them directly as above. Continue with Customize the SDK for public hooks and component contracts, and Sessions and operations for snapshot policies. Snapshots preserve files, not processes, memory, or sockets.

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What the factory supplies

Build the default components explicitly

Change one component without rebuilding everything

​What the factory supplies

​Build the default components explicitly

​Change one component without rebuilding everything

What the factory supplies

Build the default components explicitly

Change one component without rebuilding everything