chore(vendor): import pi 0.85.1

Imported as a linear vendor commit so forge rebases do not replay the upstream root tree.

git-subtree-dir: third_party/pi

git-subtree-split: d981de1229ef899957bbe968bc8dcda02a21f477

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

@@ -0,0 +1,34 @@
+import type { Skill } from "./types.ts";
+
+export function formatSkillsForSystemPrompt(skills: Skill[]): string {
+	const visibleSkills = skills.filter((skill) => !skill.disableModelInvocation);
+	if (visibleSkills.length === 0) return "";
+
+	const lines = [
+		"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>",
+	];
+
+	for (const skill of visibleSkills) {
+		lines.push("  <skill>");
+		lines.push(`    <name>${escapeXml(skill.name)}</name>`);
+		lines.push(`    <description>${escapeXml(skill.description)}</description>`);
+		lines.push(`    <location>${escapeXml(skill.filePath)}</location>`);
+		lines.push("  </skill>");
+	}
+
+	lines.push("</available_skills>");
+	return lines.join("\n");
+}
+
+function escapeXml(value: string): string {
+	return value
+		.replace(/&/g, "&amp;")
+		.replace(/</g, "&lt;")
+		.replace(/>/g, "&gt;")
+		.replace(/"/g, "&quot;")
+		.replace(/'/g, "&apos;");
+}