1 files changed, 107 insertions, 0 deletions
diff --git a/packages/kernel/src/host/dag.test.ts b/packages/kernel/src/host/dag.test.ts
new file mode 100644
index 0000000..1a0431f
--- /dev/null
+++ b/packages/kernel/src/host/dag.test.ts
@@ -0,0 +1,107 @@
+import { describe, expect, it } from "vitest";
+import type { Manifest } from "../contracts/extension.js";
+import { resolveActivationOrder } from "./dag.js";
+
+function manifest(id: string, deps?: readonly string[]): Manifest {
+	const base: Manifest = {
+		id,
+		name: id,
+		version: "1.0.0",
+		apiVersion: "^0.1.0",
+		trust: "bundled",
+	};
+	if (deps !== undefined) {
+		return { ...base, dependsOn: deps };
+	}
+	return base;
+}
+
+describe("resolveActivationOrder", () => {
+	it("returns empty array for no extensions", () => {
+		expect(resolveActivationOrder([])).toEqual([]);
+	});
+
+	it("returns a single extension with no deps", () => {
+		const result = resolveActivationOrder([manifest("a")]);
+		expect(result.map((m) => m.id)).toEqual(["a"]);
+	});
+
+	it("orders a linear chain (A → B → C)", () => {
+		const a = manifest("a");
+		const b = manifest("b", ["a"]);
+		const c = manifest("c", ["b"]);
+
+		const result = resolveActivationOrder([c, b, a]);
+		const ids = result.map((m) => m.id);
+
+		expect(ids.indexOf("a")).toBeLessThan(ids.indexOf("b"));
+		expect(ids.indexOf("b")).toBeLessThan(ids.indexOf("c"));
+	});
+
+	it("orders a diamond (A → B, A → C, B → D, C → D)", () => {
+		const a = manifest("a");
+		const b = manifest("b", ["a"]);
+		const c = manifest("c", ["a"]);
+		const d = manifest("d", ["b", "c"]);
+
+		const result = resolveActivationOrder([d, c, b, a]);
+		const ids = result.map((m) => m.id);
+
+		expect(ids.indexOf("a")).toBeLessThan(ids.indexOf("b"));
+		expect(ids.indexOf("a")).toBeLessThan(ids.indexOf("c"));
+		expect(ids.indexOf("b")).toBeLessThan(ids.indexOf("d"));
+		expect(ids.indexOf("c")).toBeLessThan(ids.indexOf("d"));
+	});
+
+	it("handles independent sets (no deps between them)", () => {
+		const a = manifest("a");
+		const b = manifest("b");
+		const c = manifest("c");
+
+		const result = resolveActivationOrder([a, b, c]);
+		expect(result).toHaveLength(3);
+		expect(result.map((m) => m.id).sort()).toEqual(["a", "b", "c"]);
+	});
+
+	it("throws on a cycle (A → B → A)", () => {
+		const a = manifest("a", ["b"]);
+		const b = manifest("b", ["a"]);
+
+		expect(() => resolveActivationOrder([a, b])).toThrow(/cycle/i);
+	});
+
+	it("throws on a larger cycle (A → B → C → A)", () => {
+		const a = manifest("a", ["c"]);
+		const b = manifest("b", ["a"]);
+		const c = manifest("c", ["b"]);
+
+		expect(() => resolveActivationOrder([a, b, c])).toThrow(/cycle/i);
+	});
+
+	it("throws on a missing dependency", () => {
+		const a = manifest("a", ["nonexistent"]);
+
+		expect(() => resolveActivationOrder([a])).toThrow(/not available/);
+	});
+
+	it("throws on duplicate extension ids", () => {
+		const a1 = manifest("a");
+		const a2 = manifest("a");
+
+		expect(() => resolveActivationOrder([a1, a2])).toThrow(/duplicate/i);
+	});
+
+	it("handles mixed independent and dependent extensions", () => {
+		const a = manifest("a");
+		const b = manifest("b", ["a"]);
+		const c = manifest("c");
+		const d = manifest("d", ["c"]);
+
+		const result = resolveActivationOrder([a, b, c, d]);
+		const ids = result.map((m) => m.id);
+
+		expect(ids.indexOf("a")).toBeLessThan(ids.indexOf("b"));
+		expect(ids.indexOf("c")).toBeLessThan(ids.indexOf("d"));
+		expect(result).toHaveLength(4);
+	});
+});