> ## Documentation Index
> Fetch the complete documentation index at: https://docs.checkfu.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Execution integration boundaries

> How Cloudflare execution, custom Harnesses and retained resources fit together.

The former third-party sandbox-provider authoring route is being retired.
Checkfu does not offer a new sandbox-provider author kit or registration flow.
The execution direction is Checkfu-managed Cloudflare or a customer-owned
Cloudflare installation.

## Custom Harnesses remain separate

A custom Harness declares its required execution capabilities and owns its
native behavior. BYOH is not a sandbox-provider selection. A custom Harness
must run within the selected Environment's execution, networking and resource
requirements; it does not bypass current permissions or machine ownership.

## Execution and cleanup

Provider configuration and an adapter's presence do not establish that a
Workspace can execute a workload. Use the exact deployment's
[capability status](/getting-started/status), including prerequisites and
availability.

Retirement must preserve the identity and cleanup obligations of existing
allocations. Unknown allocation or stop results must remain unresolved rather
than authorizing a replacement or dropping cleanup. This does not make a
retired route available for new work.

See [Environment and execution selection](/concepts/sandbox-defaults) for the
current execution direction and the distinctions between history, files,
checkpoints and process recovery.


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