fix(builder): correct move and sortable behavior

packages/blocks/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@wrnexus/blocks",
-  "version": "0.1.0",
+  "version": "0.1.1",
   "type": "module",
   "description": "Pure dynamic block document engine for WRNexus builders.",
   "exports": {

packages/blocks/src/commands.ts

@@ -17,6 +17,7 @@ export type BlockCommand =
   | { type: "insert"; location: BlockLocation; nodes: BlockNode[] }
   | { type: "remove"; nodeIds: string[] }
   | { type: "move"; intent: MoveIntent }
+  | { type: "duplicate"; nodeIds: string[]; ids: string[] }
   | { type: "updateProps"; nodeId: string; patch: JsonObject }
   | { type: "updateStyles"; nodeId: string; patch: BlockStyles }
   | { type: "replace"; nodeId: string; node: BlockNode }
@@ -152,9 +153,15 @@ export function applyCommand(
             },
           ],
         };
+    const removedBeforeDestination = command.intent.from.filter(
+      (location) =>
+        location.parentId === command.intent.to.parentId &&
+        location.slot === command.intent.to.slot &&
+        location.index < command.intent.to.index,
+    ).length;
     root = insert(
       remove(root, new Set(command.intent.nodeIds)),
-      command.intent.to,
+      { ...command.intent.to, index: Math.max(0, command.intent.to.index - removedBeforeDestination) },
       moving as BlockNode[],
     );
     affected = command.intent.nodeIds;
@@ -169,6 +176,29 @@ export function applyCommand(
         },
       })),
     };
+  } else if (command.type === "duplicate") {
+    const originals = command.nodeIds.map((id) => findBlock(root, id));
+    const locations = command.nodeIds.map((id) => locationOf(root, id));
+    if (originals.some((node) => !node) || locations.some((location) => !location))
+      return { ok: false, errors: [{ code: "command.missing", message: "A duplicated block does not exist.", severity: "error" }] };
+    const countNodes = (node: BlockNode): number =>
+      1 + Object.values(node.slots).flat().reduce((total, child) => total + countNodes(child), 0);
+    const requiredIds = (originals as BlockNode[]).reduce(
+      (total, node) => total + countNodes(node),
+      0,
+    );
+    if (command.ids.length !== requiredIds || new Set(command.ids).size !== command.ids.length)
+      return { ok: false, errors: [{ code: "command.ids", message: "Duplicate requires one unique id for every copied node.", severity: "error" }] };
+    const copies = duplicateNodes(originals as BlockNode[], (() => {
+      let index = 0;
+      return () => command.ids[index++]!;
+    })());
+    const commands = copies.map((node, index) => ({
+      type: "insert" as const,
+      location: { ...locations[index]!, index: locations[index]!.index + 1 },
+      nodes: [node],
+    }));
+    return applyCommand(document, { type: "batch", commands }, kind, registry);
   } else if (command.type === "updateProps") {
     const previous = findBlock(root, command.nodeId);
     if (!previous)

packages/blocks/test/engine.test.ts

@@ -137,4 +137,36 @@ describe("dynamic blocks engine", () => {
     expect(decoded.ok && decoded.value.roots[0]?.id).not.toBe(node.id);
     expect(duplicateNodes([node], id)[0]?.props).toEqual(node.props);
   });
+
+  test("moves forward within one slot without an off-by-one error", () => {
+    const document = doc();
+    document.root.slots.content = ["a", "b", "c"].map((nodeId) => ({
+      ...text.create({ id: () => nodeId }),
+      props: { text: nodeId },
+    }));
+    const moved = applyCommand(document, {
+      type: "move",
+      intent: {
+        nodeIds: ["a"],
+        from: [{ parentId: "root", slot: "content", index: 0 }],
+        to: { parentId: "root", slot: "content", index: 3 },
+      },
+    }, kind, registry);
+    expect(moved.ok && moved.value.document.root.slots.content.map((node) => node.id)).toEqual([
+      "b", "c", "a",
+    ]);
+  });
+
+  test("duplicates blocks with deterministic injected ids", () => {
+    const document = doc();
+    document.root.slots.content = [{ ...text.create({ id: () => "a" }), props: { text: "A" } }];
+    const duplicated = applyCommand(document, {
+      type: "duplicate",
+      nodeIds: ["a"],
+      ids: ["a-copy"],
+    }, kind, registry);
+    expect(duplicated.ok && duplicated.value.document.root.slots.content.map((node) => node.id)).toEqual([
+      "a", "a-copy",
+    ]);
+  });
 });