Sandbox Runtime Requirements

This document states the sandbox environment as a contract. The sandbox owner must meet this contract. The Paperclip runtime does not build the environment at exec time. The environment is a requirement, not a build step.

This document states requirements. It does not state build steps.

bwrap prerequisites (advisory, optional)

A sandbox provider can wrap a command with an advisory bubblewrap (bwrap) wrapper. The wrapper is advisory, best-effort, and automatic. It adds no security. The ephemeral sandbox model stays the only security posture. A missing prerequisite degrades to the plain command. It never fails the lease. Daytona is the current provider with bwrap support.

The wrapper needs three run-time prerequisites. Each prerequisite is a fact of the image or snapshot, not a fact of the runtime code. The runtime does not build the image or snapshot. The runtime only probes for the capability and degrades when the capability is absent. So each prerequisite is an owner responsibility under the requirement-not-build contract above:

The bubblewrap package is installed, and the bwrap binary is on the PATH (normally /usr/bin/bwrap).
A passwordless sudo rule lets the sandbox user run bwrap as root.
The host and kernel allow an unprivileged user namespace.

The owner supplies these prerequisites through the image or snapshot. The provider README states the distro-specific install commands, the exact sudoers rule, the user-namespace setting, and the verification command. The install and the sudoers change are environment provisioning at the image or snapshot layer. Route them to DevOps through the board. Do not add a provisioning script to the repository.

Required on PATH

node must be installed and on the PATH.
Each agent CLI that the run uses must be installed and on the PATH. The set of agent CLIs includes claude, codex, gemini, and similar CLIs.
The owner installs only the CLIs that the run uses. The owner does not need to install a CLI that no run uses.

Runtime dependencies

The sandbox execution and synchronization paths need more than node and the agent CLIs. The owner must also supply these:

A POSIX shell as sh, normally /bin/sh. The runtime runs each command with sh -c <script>. The runtime uses bash only when the adapter sets the shell to bash.
tar. The synchronization path extracts and creates archives with tar. A sandbox without tar cannot receive or return workspace files.
A writable workspace directory. The runtime extracts the workspace archive into this directory.
A writable home directory. The agent CLIs write state and credentials under the home directory.
A writable cache directory and a writable temporary directory. The runtime and the agent CLIs write intermediate files to these locations.

Detection contract

Paperclip probes each CLI before launch. Paperclip uses the same detection pattern that the runtime Dockerfiles use:

bash

command -v <cmd> || exit 1

Paperclip probes each CLI with command -v <cmd>. Paperclip fails loudly when the CLI is absent and no install command is configured for the CLI.

Optional CLI installation

An adapter can configure an install command for a CLI. When an install command is configured, the runtime obeys this flow:

The runtime probes the CLI with command -v <cmd>.
If the CLI is already on the PATH, the runtime skips the install.
If the CLI is absent, the runtime runs the configured install command one time.
A failed install is not fatal. The runtime writes a log line and continues. The launch-time probe still reports a missing CLI and fails loudly.

An owner who relies on a configured install command must also supply the network access, the filesystem write access, and the package tooling that the install command needs. When no install command is configured, the runtime does not install the CLI. The owner must supply the CLI on the PATH.

Firm rule

The Paperclip runtime never modifies the login profile. The runtime never writes a profile file. The runtime never writes an rc file.
The Paperclip runtime never sources nvm on the exec path.
The sandbox owner supplies a ready PATH. The PATH must resolve node and each used agent CLI without any action from the runtime, except for a configured install command.