test: add vitest baseline for critical payment and auth guards

tests/convex/ai-utils.test.ts

@@ -0,0 +1,22 @@
+import { describe, expect, it } from "vitest";
+import { assertNodeBelongsToCanvasOrThrow } from "@/convex/ai-utils";
+
+describe("assertNodeBelongsToCanvasOrThrow", () => {
+  it("accepts matching node/canvas relation", () => {
+    expect(() =>
+      assertNodeBelongsToCanvasOrThrow(
+        { canvasId: "canvas_a" },
+        "canvas_a",
+      ),
+    ).not.toThrow();
+  });
+
+  it("rejects mismatching node/canvas relation", () => {
+    expect(() =>
+      assertNodeBelongsToCanvasOrThrow(
+        { canvasId: "canvas_b" },
+        "canvas_a",
+      ),
+    ).toThrow("Node does not belong to canvas");
+  });
+});