the built-in archetypes come with a default prompt

docs/2-handbook/swarm/archetypes.md

@@ -81,6 +81,10 @@ archetype without `prompt` leaves the box alone.
   `refused` map. A blank `prompt` counts as none.
 - The text is a copy made at create. Editing the archetype's `prompt` later
   changes what new agents start with, not the `AGENTS.md` of agents that exist.
+- Each built-in archetype comes with a default prompt. It describes who the
+  agent is and what it cares about, and names no repo, agent or swarm path.
+  Where the files live:
+  [the implementation page](../../4-implementation/swarm/archetypes.md#the-built-in-prompts).
 
 ## How the list stays current
 

docs/4-implementation/swarm/archetypes.md

@@ -48,3 +48,10 @@ The stored value:
   "refused": { "broken": "limits: …" }
 }
 ```
+
+## The built-in prompts
+
+Each built-in archetype's `meta.prompt` is `builtins.readFile` of
+`nix/archetypes/prompts/<name>.md`. The file read gives a plain string, so
+`meta` stays plain data and the `nix eval` above prints it as JSON. The
+controller's check holds the prompt to 64 KiB.