--- title: "spawn-duplicate: a spawn for a job that already has a worker" description: "A deny rule by default: it refuses a spawn for a job that already has a worker, and names what to run instead." tags: [guard, rules, spawn-duplicate, deny] --- # spawn-duplicate A deny rule by default: it refuses a spawn for a job that already has a worker, and names what to run instead. ## What it catches A spawn for a job that already has a worker. ## Why A spawn titled `/ ` hands that job to its child. When an earlier spawn in this session was already attributed to that job and its row is still declared or running, a second worker would write the same paths from a second context. Continue the worker with a message instead, or stop it first. A running row alone does not fire it, since a row stays running after its worker dies; another session's worker is not this rule's to see. It cannot tell this session's worker that died from one still alive. ## 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({"spawn-duplicate": "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 [spawn-duplicate]: ... ``` A workspace that sets this rule to `advise` sees `advise [spawn-duplicate]: ...` instead. `magus describe rule spawn-duplicate` 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