diff --git a/src/expand.ts b/src/expand.ts
index d4109fc..c620a3d 100644
--- a/src/expand.ts
+++ b/src/expand.ts
@@ -1,8 +1,20 @@
 import { readFileSync } from "node:fs";
 import { stripFrontmatter } from "@earendil-works/pi-coding-agent";
 
+/** Skill fields needed to build the injected block (SPEC §5.3). */
+export type SkillBlockMeta = {
+	name: string;
+	filePath: string;
+	baseDir: string;
+};
+
 /** mirror agent-session `_expandSkillCommand` — SKILL.md body without YAML frontmatter (SPEC §5.3, §10). */
 export function readSkillBody(filePath: string): string {
 	const content = readFileSync(filePath, "utf-8");
 	return stripFrontmatter(content).trim();
 }
+
+/** mirror agent-session `_expandSkillCommand` — XML skill block with baseDir hint (SPEC §5.3). */
+export function formatBlock(meta: SkillBlockMeta, body: string): string {
+	return `<skill name="${meta.name}" location="${meta.filePath}">\nReferences are relative to ${meta.baseDir}.\n\n${body}\n</skill>`;
+}