Unattended runs with limits

In the last lesson you ran Claude from a script. Now — a run that works unattended, for a long time, editing files. The core principle: a run like this does exactly what you allowed in advance. So allow little, and limit the rest.

Five limits

1. Minimal permissions. The dontAsk mode denies anything that would have needed a question. Allow only the folders the task edits and the one command it runs.
2. The sandbox. Let the system limit what the allowed commands can do — and do not let the run start if the sandbox is unavailable.
3. Caps. --max-turns caps the turns, --max-budget-usd the approximate cost.
4. A review gate. Deny git commit and git push. The result stays in the working tree, and you commit — after reading the diff.
5. A cost estimate. First run a small slice of the task, and set the budget limit from that.

The limits file

It is handy to keep the limits in a separate file, for example .claude/bounded-run.json:

{
  "permissions": {
    "allow": ["Edit(./src/**)", "Edit(./test/**)", "Bash(npm test *)"],
    "deny": ["Agent", "Read(./.env)", "Read(./.env.*)", "Bash(git commit *)", "Bash(git push *)"]
  },
  "sandbox": {
    "enabled": true,
    "failIfUnavailable": true,
    "allowUnsandboxedCommands": false
  }
}

• a deny on Agent stops Claude from handing work to a subagent, which might have its own permission mode;
• failIfUnavailable — do not start without the sandbox;
• allowUnsandboxedCommands: false — do not retry a command outside the sandbox.

The run

claude -p "Add a test for one uncovered function in src/links.js" \
  --setting-sources project \
  --settings .claude/bounded-run.json \
  --permission-mode dontAsk \
  --model sonnet \
  --max-turns 15 \
  --max-budget-usd 2 \
  --output-format json

--setting-sources project leaves out your personal settings — for example, a permission saved with “Yes, and don’t ask again”. Only what you explicitly wrote into the limits gets in.

When a limit is hit, the exit code is non-zero, and subtype in the JSON explains why: error_max_turns or error_max_budget_usd. The total_cost_usd field is a client-side estimate, not your bill.

You are the review gate

After the run, read git status and git diff, including the limits file itself, run the tests yourself, and commit only what you accept. For a second opinion, ask a fresh Claude session to review the diff in a clean context.