---
title: "background-left: an agent finishing while shell commands it ran in the background are still running"
description: "A deny rule by default: it refuses an agent finishing while shell commands it ran in the background are still running, and names what to run instead."
tags: [guard, rules, background-left, deny]
---

# background-left

A deny rule by default: it refuses an agent finishing while shell commands it ran in the background are still running, and names what to run instead.

## What it catches

An agent finishing while shell commands it ran in the background are still running.

## Why

A host does not stop a finished subagent's background tasks, and once the subagent has reported nobody is told when one ends or that it is still running: a transcript search left behind by a scout ran for four hours. At a subagent's stop magus reads the subagent's own transcript for the shell commands it ran in the background (run_in_background, a foreground call the host moved to the background, a watcher's command) that no completion notice, stop call or watcher expiry has ended, and refuses the stop naming each by id, start time, age and command. A run under `magus job exec --timeout`, which check-timeout sends a worker to background and which stops at its deadline, and a commit the host moved to the background while its hooks run, end on their own: their completion notice is how the agent hears the result, so neither holds a stop. At a root session's stop it advises instead, and only of tasks older than 30 minutes: a root wakes on a task's completion notice, so a young task is one it is waiting on, and the person is there to decide. Reads the host's transcript by shape, so a host whose transcript records no background task in that shape is never refused. Set to advise, a subagent's stop is advised too.

## Default and override

By default this rule takes the decision `deny`. A workspace sets it by name, in its root
magusfile, to `deny`, `advise` or `off`:

```buzz
magus\guard.builtins({"background-left": "advise"})
```

A loosening takes effect once it is committed; a tightening applies at once.

## Seeing it

A verdict names its rule in brackets, which is how you got here:

```text
deny [background-left]: ...
```

A workspace that sets this rule to `advise` sees `advise [background-left]: ...` instead.

`magus describe rule background-left` prints the same entry at a terminal, and
`magus describe rules` lists every rule this workspace enforces.

## See also

- [All rules](index.md) - what this workspace enforces, deny first
- [The guard](../../guides/integrations/agents/guard.md) - how a verdict is reached and wired
- [Setting a built-in rule](../../guides/integrations/agents/guard.md#setting-a-built-in-rule) - how a workspace changes this default