an archetype's prompt prefills the new agent's agents.md in the create form

frontend/packages/swarm-ui/src/pages/CreateAgentAgentsMd.ts

@@ -21,3 +21,17 @@ export function agentsMdRefusal(problem: ProblemDetails): string | null {
     ? problem.detail
     : null;
 }
+
+/**
+ * The AGENTS.md box after the archetype pick changes from one whose prompt was
+ * `previous` to one whose prompt is `next` (both `""` for none). The pick
+ * replaces what is in the box only when the box is empty or still holds the
+ * previous pick's prompt; text the operator typed or edited stays.
+ */
+export function agentsMdAfterPick(
+  current: string,
+  previous: string,
+  next: string,
+): string {
+  return current.trim() === "" || current === previous ? next : current;
+}

frontend/packages/swarm-ui/src/pages/CreateAgentArchetype.ts

@@ -15,6 +15,7 @@ export interface Archetype {
     subagent_models?: string[];
     max_subagents?: number;
   };
+  prompt?: string;
 }
 
 // Mirrors swarm-controller's `Archetypes`.

frontend/packages/swarm-ui/src/pages/CreateAgentForm.tsx

@@ -63,7 +63,11 @@ import {
   requestArchetype,
   type ArchetypeList,
 } from "./CreateAgentArchetype.js";
-import { agentsMdBody, agentsMdRefusal } from "./CreateAgentAgentsMd.js";
+import {
+  agentsMdAfterPick,
+  agentsMdBody,
+  agentsMdRefusal,
+} from "./CreateAgentAgentsMd.js";
 import {
   NAME_PATTERN,
   nextStep,
@@ -191,13 +195,14 @@ export function CreateAgentForm({
     })().catch((e: unknown) => setArchetypesError({ detail: String(e) }));
   }, []);
 
-  // Fills permissions, caps and inference from the picked archetype; each
-  // stays editable, and the request carries only those fields.
+  // Fills permissions, caps, inference and the AGENTS.md text from the picked
+  // archetype; each stays editable, and the request carries only those fields.
   function pickArchetype(key: string) {
     setArchetype(key);
-    const p = prefill(
-      archetypes?.archetypes.find((a) => archetypeKey(a) === key),
-      catalogue?.default ?? [],
+    const next = archetypes?.archetypes.find((a) => archetypeKey(a) === key);
+    const p = prefill(next, catalogue?.default ?? []);
+    setAgentsMd((current) =>
+      agentsMdAfterPick(current, picked?.prompt ?? "", next?.prompt ?? ""),
     );
     setSelected(p.permissions);
     setCpu(p.cpu);
@@ -401,7 +406,8 @@ export function CreateAgentForm({
             <div class="create-agent-fields">
               <p class="create-agent-intro">
                 The text the agent's AGENTS.md starts with. Optional: leave it
-                empty and the agent starts without the file.
+                empty and the agent starts without the file. An archetype with a
+                prompt fills the box in; edit it freely.
               </p>
               <TextAreaField
                 id="agent-agents-md"

frontend/packages/swarm-ui/test/create-agents-md.test.mjs

@@ -5,6 +5,7 @@
 import assert from "node:assert/strict";
 import { test } from "node:test";
 import {
+  agentsMdAfterPick,
   agentsMdBody,
   agentsMdRefusal,
 } from "../src/pages/CreateAgentAgentsMd.ts";
@@ -41,3 +42,29 @@ test("other failures stay with the general error", () => {
   assert.equal(agentsMdRefusal({ status: 400 }), null);
   assert.equal(agentsMdRefusal({ detail: "agents_md is too long" }), null);
 });
+
+test("a pick fills an empty box with the archetype's prompt", () => {
+  assert.equal(agentsMdAfterPick("", "", "Review only."), "Review only.");
+  assert.equal(agentsMdAfterPick(" \n", "", "Review only."), "Review only.");
+});
+
+test("a pick keeps text the operator typed or edited", () => {
+  assert.equal(agentsMdAfterPick("# mine", "", "Review only."), "# mine");
+  assert.equal(
+    agentsMdAfterPick("Review only. Also x.", "Review only.", "Triage."),
+    "Review only. Also x.",
+  );
+});
+
+test("a pick over an unedited prefill swaps it, and none clears it", () => {
+  assert.equal(
+    agentsMdAfterPick("Review only.", "Review only.", "Triage."),
+    "Triage.",
+  );
+  assert.equal(agentsMdAfterPick("Review only.", "Review only.", ""), "");
+});
+
+test("an archetype without a prompt leaves the box as it is", () => {
+  assert.equal(agentsMdAfterPick("# mine", "", ""), "# mine");
+  assert.equal(agentsMdAfterPick("", "", ""), "");
+});