test(agent): pin harness resource formatting

packages/agent/src/harness/prompt-templates.ts

@@ -169,7 +169,7 @@ function errorMessage(error: unknown, fallback: string): string {
 	return error instanceof Error ? error.message : fallback;
 }
 
-/** Parse slash-command arguments using simple shell-style single and double quotes. */
+/** Parse an argument string using simple shell-style single and double quotes. */
 export function parseCommandArgs(argsString: string): string[] {
 	const args: string[] = [];
 	let current = "";

packages/agent/src/harness/system-prompt.ts

@@ -6,7 +6,7 @@ export function formatSkillsForSystemPrompt(skills: Skill[]): string {
 
 	const lines = [
 		"The following skills provide specialized instructions for specific tasks.",
-		"Use the read tool to load a skill's file when the task matches its description.",
+		"Read the full skill file when the task matches its description.",
 		"When a skill file references a relative path, resolve it against the skill directory (parent of SKILL.md / dirname of the path) and use that absolute path in tool commands.",
 		"",
 		"<available_skills>",

packages/agent/src/harness/types.ts

@@ -2,9 +2,14 @@ import type { ImageContent, Model, TextContent } from "@earendil-works/pi-ai";
 import type { AgentEvent, AgentMessage, AgentTool, ThinkingLevel } from "../index.js";
 import type { Session } from "./session/session.js";
 
-/** Model-visible skill loaded from a `SKILL.md` file or provided by an application. */
+/**
+ * Skill loaded from a `SKILL.md` file or provided by an application.
+ *
+ * `name`, `description`, and `filePath` are inserted into the system prompt in an XML-formatted block as suggested by agentskills.io.
+ * Use {@link formatSkillsForSystemPrompt} to generate the spec-compatible system prompt block.
+ */
 export interface Skill {
-	/** Skill command name. */
+	/** Stable skill name used for lookup and model-visible listings. */
 	name: string;
 	/** Short model-visible description of when to use the skill. */
 	description: string;
@@ -16,19 +21,19 @@ export interface Skill {
 	disableModelInvocation?: boolean;
 }
 
-/** Prompt template that can expand slash-command text before a prompt is sent. */
+/** Prompt template that can be formatted into a prompt for explicit invocation. */
 export interface PromptTemplate {
-	/** Slash-command name without the leading `/`. */
+	/** Stable template name used for lookup or application command routing. */
 	name: string;
 	/** Optional description for command lists or autocomplete. */
 	description?: string;
-	/** Template content. Argument placeholders are expanded by `formatPromptTemplateInvocation`. */
+	/** Template content. Argument placeholders are formatted by `formatPromptTemplateInvocation`. */
 	content: string;
 }
 
-/** Resources made available to harness prompt expansion and system-prompt callbacks. */
+/** Resources made available to explicit invocation methods and system-prompt callbacks. */
 export interface AgentHarnessResources {
-	/** Prompt templates used to expand `/template args` input. */
+	/** Prompt templates available for explicit invocation. */
 	promptTemplates?: PromptTemplate[];
 	/** Skills available to the model and explicit skill invocation. */
 	skills?: Skill[];

packages/agent/test/harness/system-prompt.test.ts

@@ -1,45 +1,66 @@
 import { describe, expect, it } from "vitest";
 import { formatSkillsForSystemPrompt } from "../../src/harness/system-prompt.js";
 
+const visibleSkill = {
+	name: "visible",
+	description: "Use <this> & that",
+	content: "visible content",
+	filePath: "/skills/visible/SKILL.md",
+};
+
+const secondSkill = {
+	name: "second",
+	description: "Second skill",
+	content: "second content",
+	filePath: "/skills/second/SKILL.md",
+};
+
+const disabledSkill = {
+	name: "hidden",
+	description: "Hidden",
+	content: "hidden content",
+	filePath: "/skills/hidden/SKILL.md",
+	disableModelInvocation: true,
+};
+
 describe("formatSkillsForSystemPrompt", () => {
-	it("formats visible skills and skips model-disabled skills", () => {
+	it("formats visible skills in order and skips model-disabled skills", () => {
+		expect(formatSkillsForSystemPrompt([visibleSkill, disabledSkill, secondSkill])).toBe(
+			`The following skills provide specialized instructions for specific tasks.
+Read the full skill file when the task matches its description.
+When a skill file references a relative path, resolve it against the skill directory (parent of SKILL.md / dirname of the path) and use that absolute path in tool commands.
+
+<available_skills>
+  <skill>
+    <name>visible</name>
+    <description>Use &lt;this&gt; &amp; that</description>
+    <location>/skills/visible/SKILL.md</location>
+  </skill>
+  <skill>
+    <name>second</name>
+    <description>Second skill</description>
+    <location>/skills/second/SKILL.md</location>
+  </skill>
+</available_skills>`,
+		);
+	});
+
+	it("returns an empty string when no skills are model-visible", () => {
+		expect(formatSkillsForSystemPrompt([disabledSkill])).toBe("");
+	});
+
+	it("escapes XML in all model-visible skill fields", () => {
 		expect(
 			formatSkillsForSystemPrompt([
 				{
-					name: "visible",
-					description: "Use <this> & that",
-					content: "visible content",
-					filePath: "/skills/visible/SKILL.md",
-				},
-				{
-					name: "hidden",
-					description: "Hidden",
-					content: "hidden content",
-					filePath: "/skills/hidden/SKILL.md",
-					disableModelInvocation: true,
+					name: "a&b",
+					description: `Quote "double" and 'single'`,
+					content: "content",
+					filePath: '/skills/<bad>&"quote"/SKILL.md',
 				},
 			]),
-		).toContain("<name>visible</name>");
-		expect(
-			formatSkillsForSystemPrompt([
-				{
-					name: "visible",
-					description: "Use <this> & that",
-					content: "visible content",
-					filePath: "/skills/visible/SKILL.md",
-				},
-			]),
-		).toContain("Use &lt;this&gt; &amp; that");
-		expect(
-			formatSkillsForSystemPrompt([
-				{
-					name: "hidden",
-					description: "Hidden",
-					content: "hidden content",
-					filePath: "/skills/hidden/SKILL.md",
-					disableModelInvocation: true,
-				},
-			]),
-		).toBe("");
+		).toContain(
+			"<name>a&amp;b</name>\n    <description>Quote &quot;double&quot; and &apos;single&apos;</description>\n    <location>/skills/&lt;bad&gt;&amp;&quot;quote&quot;/SKILL.md</location>",
+		);
 	});
 });