feat(builder): add dynamic blocks email and dnd packages

packages/dnd/test/reorder.test.ts

@@ -0,0 +1,31 @@
+import { describe, expect, test } from "bun:test";
+import { deepestValidTarget, reorderGroups, visualIndex } from "../src/index.ts";
+
+describe("dnd pure behavior", () => {
+  test("moves across groups without mutation", () => {
+    const input = new Map([
+      ["a", ["1", "2"]],
+      ["b", ["3"]],
+    ]);
+    const result = reorderGroups(input, {
+      ids: ["2"],
+      from: [{ group: "a", index: 1 }],
+      to: { group: "b", index: 0 },
+    });
+    expect(result.get("a")).toEqual(["1"]);
+    expect(result.get("b")).toEqual(["2", "3"]);
+    expect(input.get("a")).toEqual(["1", "2"]);
+  });
+  test("mirrors horizontal RTL index", () =>
+    expect(visualIndex(0, 4, "horizontal", "rtl")).toBe(3));
+  test("selects deepest valid target", () =>
+    expect(
+      deepestValidTarget(
+        [
+          { depth: 1, location: { group: "a", index: 0 } },
+          { depth: 3, location: { group: "b", index: 0 } },
+        ],
+        (location) => location.group === "b",
+      )?.depth,
+    ).toBe(3));
+});