Phase 12: skill name collision warn — SPEC §11.

Duplicate names in resourceLoader resolve to the first skill with a one-time UI warning during re-inject expansion.

Co-authored-by: Cursor <cursoragent@cursor.com>

test/reinject-collision.test.ts

@@ -0,0 +1,31 @@
+import { describe, expect, it, vi } from "vitest";
+import { registeredSkillsByName } from "../src/reinject";
+
+describe("registeredSkillsByName", () => {
+	it("keeps the first skill when names collide", () => {
+		const first = { name: "alpha", filePath: "/a/SKILL.md", baseDir: "/a" };
+		const second = { name: "alpha", filePath: "/b/SKILL.md", baseDir: "/b" };
+
+		const byName = registeredSkillsByName([first, second]);
+
+		expect(byName.get("alpha")).toBe(first);
+	});
+
+	it("warns once per duplicate name", () => {
+		const notify = vi.fn();
+		const ctx = { hasUI: true, ui: { notify } } as never;
+		const skills = [
+			{ name: "alpha", filePath: "/a/SKILL.md", baseDir: "/a" },
+			{ name: "alpha", filePath: "/b/SKILL.md", baseDir: "/b" },
+			{ name: "alpha", filePath: "/c/SKILL.md", baseDir: "/c" },
+		];
+
+		registeredSkillsByName(skills, ctx);
+
+		expect(notify).toHaveBeenCalledTimes(1);
+		expect(notify).toHaveBeenCalledWith(
+			'skill-reinject: duplicate skill name "alpha" — using first from resourceLoader',
+			"warning",
+		);
+	});
+});