regenrek/codex-sandbox

Codex Sandboxes

Create one directory per task and run the agent inside that directory. Prefer this over git worktrees when:

• Codex or other agents sometimes use the wrong current working directory.
• You want full isolation for .env, node_modules, build outputs, ports, and dev servers.
• You want a simple mental model: one task equals one folder equals one branch.

This skill bundles a small Python CLI plus a Bash wrapper:

• scripts/codex_sandbox.py (primary)
• scripts/codex-task (convenience)

Locate the skill directory

Run the scripts from the skill folder, depending on where you installed it:

• Repo-scoped: $REPO_ROOT/.codex/skills/codex-sandboxes
• User-scoped: $CODEX_HOME/skills/codex-sandboxes (macOS/Linux default: ~/.codex/skills/codex-sandboxes)

Use git rev-parse --show-toplevel to get $REPO_ROOT.

Quick start (agent-only)

This skill is always invoked by an agent. Do not run it manually.

Example command the agent should run:

SKILL_DIR="$(git rev-parse --show-toplevel)/.codex/skills/codex-sandboxes"
python3 "$SKILL_DIR/scripts/codex_sandbox.py" new fix-123

The command will:

1. Detect the repo remote (default: origin).
2. Create or update a local bare mirror.
3. Clone a sandbox directory under a base directory.
4. Create/switch to a task branch from origin/main.
5. Set upstream tracking to origin/<branch> (pushes once if needed).
6. Install safety hooks that block commit/push on main/master.

How to instruct the agent

Always request this via the agent. Provide:

• Task name (used for sandbox + branch name).
• Any non-default base directory (e.g. --base-dir ~/projects).
• Any non-default base branch or remote.

If you do not provide extra details, the agent should use defaults. If the task name is ambiguous or missing, the agent should ask back.

Example prompt to the agent:

Use codex-sandbox to create a sandbox for task "fix-123".
Place it under ~/projects, base branch main.
Command: python3 <skill_dir>/scripts/codex_sandbox.py new fix-123 --base-dir ~/projects --base-branch main

Concepts

Use these terms consistently in prompts and logs:

• Workset: Logical grouping for a ticket/feature (optional label only).
• Sandbox: One clone directory used by one writing agent.
• Session: One Codex process running in one sandbox.

Prefer: one writing session per sandbox.

Create a sandbox

python3 <skill_dir>/scripts/codex_sandbox.py new <task> [options]

Common patterns:

# Create sandbox + branch and print its path
python3 <skill_dir>/scripts/codex_sandbox.py new feat-auth

# Use a different base branch
python3 <skill_dir>/scripts/codex_sandbox.py new fix-123 --base-branch develop

# Copy .env.example to .env on creation
python3 <skill_dir>/scripts/codex_sandbox.py new feat-auth --env-copy

Key options:

• --base-dir DIR: Where to place sandboxes (default: ~/wip).
• --bare-dir DIR: Where to keep the bare mirror (default: ~/.cache/codex-sandboxes/<repo>.git).
• --remote NAME: Which remote to use (default: origin).
• --remote-url URL: Override remote URL discovery.
• --base-branch NAME: Base branch to branch from (default: main).
• --branch NAME: Explicit branch name (default: derived from <task>).
• --env-copy: Copy .env.example to .env if present and .env missing.

List, inspect, remove

python3 <skill_dir>/scripts/codex_sandbox.py list
python3 <skill_dir>/scripts/codex_sandbox.py path <task>
python3 <skill_dir>/scripts/codex_sandbox.py status <task>
python3 <skill_dir>/scripts/codex_sandbox.py rm <task>

Safety rules

Follow these rules in every run:

• Never run a write-capable agent in the primary checkout.
• Always create a sandbox for a write task.
• Keep one writer per sandbox.
• Keep main/master protected on the remote (PR-only merges).

If the sandbox is currently on main/master, the tool will refuse to proceed unless you pass --allow-main.

Multiple sessions

If you want multiple sessions for one workset, create multiple sandboxes:

python3 <skill_dir>/scripts/codex_sandbox.py new feat-auth-ui-1
python3 <skill_dir>/scripts/codex_sandbox.py new feat-auth-ui-2
python3 <skill_dir>/scripts/codex_sandbox.py new feat-auth-core-1

Avoid running two writing sessions in the same sandbox.

Troubleshooting

• Remote URL detection failed: pass --remote-url.
• Sandbox already exists: choose a unique <task> name or remove with rm.
• You want deterministic naming: read references/naming.md.