# @openclaw/mxc-sandbox

Official MXC sandbox execution plugin for OpenClaw.

This plugin lets OpenClaw run tool execution through MXC on Windows hosts with
ProcessContainer support.

## Install

```bash
openclaw plugins install @openclaw/mxc-sandbox
```

Restart the Gateway after installing or updating the plugin.

## Configure

After installing the plugin, configure an agent to use the `mxc` sandbox backend:

```json5
{
  agents: {
    defaults: {
      sandbox: {
        mode: "all",
        backend: "mxc",
        workspaceAccess: "none",
      },
    },
  },
}
```

This plugin is an early prerelease for testing, so expect configuration and
readiness behavior to change as MXC host support matures.

## Package

- Plugin id: `mxc`
- Package: `@openclaw/mxc-sandbox`
- Minimum OpenClaw host: `2026.6.11`

## Plugin config

`plugins.entries.mxc.config` is validated with a strict schema: unknown keys
and out-of-range values fail plugin activation with an actionable error
(`Invalid mxc plugin config: <reason>`) instead of falling back silently.

| Field            | Type                              | Default                                | Notes                                                                                                                                                         |
| ---------------- | --------------------------------- | -------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `mxcBinaryPath`  | `string`                          | unset                                  | Non-empty override for the `wxc-exec.exe` executor path; see [SDK-only executor discovery](#supported).                                                       |
| `containment`    | `"process" \| "processcontainer"` | `"process"`                            | Both currently resolve to Windows ProcessContainer.                                                                                                           |
| `network`        | `"none" \| "default"`             | `"none"`                               | `"default"` allows outbound network via the `internetClient` capability.                                                                                      |
| `timeoutSeconds` | `number`                          | unset (baseline default `300` applies) | Must be `>= 1` and `<= 2147000` (the largest Node-safe `setTimeout` delay in whole seconds). Capped to the sandbox policy baseline timeout when both are set. |
| `debug`          | `boolean`                         | `false`                                | Forwards debug output from the MXC SDK launcher.                                                                                                              |
| `mxcPolicyPaths` | `string[]`                        | unset (built-in baseline only)         | Every entry must be a non-empty absolute path. See [Sandbox policy files](#sandbox-policy-files).                                                             |

Any other key is rejected. `openclaw.plugin.json` publishes the same schema
(enums, `minimum`/`maximum` bounds) so `openclaw config` validation and CLI
help stay in sync with plugin runtime validation.

## Supported

- Windows hosts with the MXC executor installed through `@microsoft/mxc-sdk`.
- Explicit opt-in after plugin install with `sandbox.backend: "mxc"`.
- MXC `process` containment, which resolves to Windows ProcessContainer.
- `workspaceAccess`:
  - `none`: only the isolated sandbox workdir is mounted, read-only. There is
    no separate mount for the real agent workspace.
  - `ro`: the isolated sandbox workdir is mounted read-only, plus a distinct
    read-only mount of the real agent workspace whenever it differs from the
    sandbox workdir.
  - `rw`: the active agent workspace is mounted read-write. If protected
    OpenClaw skill roots (`skills`, `.agents/skills`, or the materialized
    sandbox skills workspace) exist beneath it, MXC fails the command before
    launch because ProcessContainer cannot enforce a nested read-only grant
    beneath a writable parent. The filesystem bridge also rejects writes to
    those protected paths.
  - Use policy `filesystem.additionalReadwritePaths` for additional explicit
    writable host paths shared by every MXC sandbox.
- `scope` workspace selection:
  - `session`, `agent`, and `shared` choose the OpenClaw workspace directory
    passed to MXC.
- SDK-only executor discovery from `@microsoft/mxc-sdk/bin/<arch>` or
  `@microsoft/mxc-sdk/bin`; use `mxcBinaryPath` only for an explicit override.
- OpenClaw passes per-run command, environment, and filesystem config to the
  plugin's Node launcher through a short-lived local payload file, and deletes
  that file and its temp directory when the launcher or run finishes.
- `@microsoft/mxc-sdk@0.7.0` then carries the full base64 request envelope on
  the native `wxc-exec` process argv. A host user with process-inspection rights
  can observe that command, environment, and policy data while the process is
  running. Do not put secrets in MXC command arguments or environment values
  until the SDK provides a non-argv transport
  ([microsoft/mxc#626](https://github.com/microsoft/mxc/issues/626)).

## Not supported yet

- Non-Windows hosts.
- Docker-style long-lived containers per `scope`. MXC ProcessContainer runs are
  per command; scope controls workspace reuse, not container lifetime.
- Windows filesystem-deny and host-list network policy knobs are not exposed by
  this plugin until MXC can enforce them on ProcessContainer.

## Test setup

Use an already configured OpenClaw installation with MXC installed and enabled
on a supported Windows host. These commands create a uniquely named test agent
and a new temporary workspace, leaving existing agents and workspaces alone.
[`openclaw config patch --stdin`](https://docs.openclaw.ai/cli/config#config-patch)
applies sandbox settings only to that agent. Installation-wide MXC settings
and policy files remain unchanged; review them before testing because they
apply to the test agent too.

Run setup, testing, and cleanup in the same PowerShell session. Finish cleanup
before running setup again. Stop if any command fails.

```powershell
$mxcAgentCreated = $false
$mxcAgent = "mxc-test-" + [guid]::NewGuid().ToString("N")
$mxcWorkspace = Join-Path ([System.IO.Path]::GetTempPath()) $mxcAgent
New-Item -ItemType Directory -Path $mxcWorkspace -ErrorAction Stop | Out-Null

openclaw agents add $mxcAgent `
  --workspace $mxcWorkspace `
  --non-interactive
if ($LASTEXITCODE -ne 0) { throw "Agent creation failed; stop without patching or deleting an existing agent." }
$mxcAgentCreated = $true

$mxcConfigPatch = @"
{
  agents: {
    entries: {
      "$mxcAgent": {
        sandbox: {
          mode: "all",
          backend: "mxc",
          scope: "agent",
          workspaceAccess: "none",
        },
      },
    },
  },
}
"@

$mxcConfigPatch | openclaw config patch --stdin --dry-run
if ($LASTEXITCODE -ne 0) { throw "Sandbox validation failed; use Cleanup to remove the new test agent." }
$mxcConfigPatch | openclaw config patch --stdin
if ($LASTEXITCODE -ne 0) { throw "Sandbox setup failed; use Cleanup to remove the new test agent." }
```

## Sandbox policy files

MXC reads optional host policy files listed in
`plugins.entries.mxc.config.mxcPolicyPaths`. Policy files constrain the
filesystem and process defaults used by every MXC sandbox run on the host.
Omitting `mxcPolicyPaths` (or configuring an empty array) uses the built-in
sandbox baseline only; MXC never reads an implicit user or machine policy
path.

Every `mxcPolicyPaths` entry must be a non-empty absolute path; the plugin
fails to activate with an actionable error the moment a relative, empty, or
non-string entry is configured. JSON arrays preserve order, and MXC treats
that order as the policy layering order.

Once a sandbox backend is created for an agent, MXC reads every configured
policy file and fails closed instead of silently falling back to the
baseline:

- A configured policy file that does not exist on the host is an error
  (`Configured sandbox policy file <path> does not exist. Remove it from
mxcPolicyPaths or create the file.`), not a silent skip.
- A policy file that is malformed JSON or includes an unsupported field fails
  with an error naming the policy file path and the invalid field.
- Every `filesystem.additionalReadonlyPaths` and
  `filesystem.additionalReadwritePaths` entry must be an absolute Windows path
  that exists on the host at the time the sandbox activates; a missing path
  fails with an error naming the path, the policy file, and the field.

Example policy:

```json
{
  "filesystem": {
    "restrictToProjectDir": true,
    "additionalReadonlyPaths": ["C:\\Tools\\OpenClaw\\shared-readonly"],
    "additionalReadwritePaths": ["D:\\OpenClawScratch"]
  },
  "process": {
    "timeoutSeconds": 120
  }
}
```

Policy schema:

- `filesystem.restrictToProjectDir`: `true`, default `true`. Hardening-only.
  The default already restricts the sandbox to the project/workspace directory;
  policy files can assert `true` but cannot loosen this.
- `filesystem.additionalReadonlyPaths`: `string[]`, default `[]`. Extra host
  paths to expose read-only. Each path must be absolute and must already
  exist on the host.
- `filesystem.additionalReadwritePaths`: `string[]`, default `[]`. Extra host
  paths to expose read-write. Each path must be absolute and must already
  exist on the host, and must not overlap read-only roots or protected skill
  overlays.
- `process.timeoutSeconds`: positive `number`, default `300`. Per-command upper
  bound. Values must be finite and at least `1`.

Only the `filesystem` and `process` sections are supported. Unknown sections or
unknown fields are rejected so policy files fail closed when they drift from the
implemented MXC ProcessContainer surface.

When multiple configured policy files exist, OpenClaw layers them
deterministically in `mxcPolicyPaths` array order:

- readonly and read-write path arrays are appended and de-duplicated while
  preserving first-seen order.
- the effective timeout is the smallest value from the default and configured
  policy files.
- `restrictToProjectDir` remains enabled because the field is hardening-only.

The filesystem bridge keeps protected OpenClaw skill overlays read-only. For
command execution, MXC fails closed before launch when `workspaceAccess: "rw"`
or a configured read-write path overlaps a protected skill root, because
ProcessContainer cannot safely enforce the nested read-only grant.

Run the TUI as that agent:

```powershell
openclaw tui --session "agent:${mxcAgent}:main"
```

For local embedded testing without a Gateway:

```powershell
openclaw tui --local --session "agent:${mxcAgent}:main"
```

## Cleanup

In the same PowerShell session, remove only the agent created by setup:

```powershell
if (-not $mxcAgentCreated) {
  throw "No successfully created test agent in this session; do not delete an existing agent."
}
openclaw agents delete $mxcAgent --force
if ($LASTEXITCODE -ne 0) { throw "Agent cleanup failed; inspect the error before retrying." }
$mxcAgentCreated = $false
```

The delete command removes the test agent's configuration and attempts to move
its workspace and state to Trash. Check its output for any manual-cleanup
warning. Do not remove the MXC plugin entry or shared policy files: other
agents may still use them.

## Host readiness

IsoEnvBroker must be available on the host OS. The plugin checks this before
registering the sandbox backend.

Host preparation is advisory. If directory listing inside the sandbox fails with
`Access is denied`, run this once from an elevated prompt:

```powershell
wxc-host-prep prepare-system-drive
```

`wxc-host-prep` ships with `@microsoft/mxc-sdk` under
`node_modules/@microsoft/mxc-sdk/bin/<arch>/`.

## Testing

```powershell
pnpm test:extension mxc
```

`pnpm test extensions/mxc` is also supported for the bundled extension test lane.

For policy-only edits, the focused coverage is in:

```powershell
pnpm test:extension mxc extensions/mxc/test/config.test.ts extensions/mxc/test/sandbox-policy-loader.test.ts extensions/mxc/test/mxc-backend.test.ts
```
