frontend/src/features/workspace/DocumentEditor.tsx

@@ -1072,22 +1072,60 @@ export const DocumentEditor: React.FC<DocumentEditorProps> = ({
   );
 
   const handleMoveBlock = useCallback(
-    (blockId: string, newIndex: number, level?: number) => {
+    (blockId: string, targetIndex: number, newLevel?: number) => {
       if (!effectiveCanEdit) return;
       setBlocks((prev) => {
         const fromIdx = prev.findIndex((b) => b.id === blockId);
         if (fromIdx === -1) return prev;
+
+        const parentBlock = prev[fromIdx];
+        const parentLevel = Math.max(0, parentBlock.level || 0);
+
+        // Calculate full subtree count (dragged block + all contiguous descendants)
+        let count = 1;
+        for (let i = fromIdx + 1; i < prev.length; i++) {
+          if (Math.max(0, prev[i].level || 0) > parentLevel) {
+            count++;
+          } else {
+            break;
+          }
+        }
+
+        // Prevent dropping inside its own subtree
+        if (targetIndex >= fromIdx && targetIndex < fromIdx + count) {
+          return prev;
+        }
+
         const copy = [...prev];
-        const [moving] = copy.splice(fromIdx, 1);
-        const updatedMoving: DocumentBlock = {
-          ...moving,
-          level: level !== undefined ? level : moving.level,
-        };
-        const boundedIdx = Math.max(0, Math.min(newIndex, copy.length));
-        copy.splice(boundedIdx, 0, updatedMoving);
+        const subtree = copy.splice(fromIdx, count);
+
+        // Adjust insertion index because removing elements from before shifts target index
+        let insertIndex = targetIndex;
+        if (fromIdx < targetIndex) {
+          insertIndex = targetIndex - count;
+        }
+        insertIndex = Math.max(0, Math.min(insertIndex, copy.length));
+
+        // Calculate level adjustments if moving to a constrained position
+        const prevBlockInPosition = insertIndex > 0 ? copy[insertIndex - 1] : null;
+        const maxAllowed = prevBlockInPosition
+          ? Math.max(0, prevBlockInPosition.level || 0) + 1
+          : 0;
+
+        const targetLevel = newLevel !== undefined ? newLevel : parentLevel;
+        const clampedLevel = Math.min(targetLevel, maxAllowed);
+        const levelDelta = clampedLevel - parentLevel;
+
+        const updatedSubtree = subtree.map((b) => ({
+          ...b,
+          level: Math.max(0, (b.level || 0) + levelDelta),
+        }));
+
+        copy.splice(insertIndex, 0, ...updatedSubtree);
         const normalized = ensureNonEmptyBlocks(docId, copy);
+
         if (isLiveEnabled) {
-          sendBlockMoved(blockId, boundedIdx, updatedMoving.level, normalized);
+          sendBlockMoved(blockId, insertIndex, updatedSubtree[0].level, normalized);
         }
         return normalized;
       });

frontend/src/features/workspace/OutlinerTree.tsx

@@ -282,10 +282,29 @@ export const OutlinerTree: React.FC<OutlinerTreeProps> = ({
     setDraggedIndex(index);
   }, []);
 
-  const handleDragOverBlock = useCallback((e: React.DragEvent, index: number) => {
-    e.preventDefault();
-    setDragOverIndex(index);
-  }, []);
+  const handleDragOverBlock = useCallback(
+    (e: React.DragEvent, index: number) => {
+      e.preventDefault();
+      if (draggedIndex !== null) {
+        const parentLevel = Math.max(0, blocks[draggedIndex]?.level || 0);
+        let count = 1;
+        for (let i = draggedIndex + 1; i < blocks.length; i++) {
+          if (Math.max(0, blocks[i].level || 0) > parentLevel) {
+            count++;
+          } else {
+            break;
+          }
+        }
+        // Do not allow dropping inside its own subtree (self or descendants)
+        if (index >= draggedIndex && index < draggedIndex + count) {
+          setDragOverIndex(null);
+          return;
+        }
+      }
+      setDragOverIndex(index);
+    },
+    [blocks, draggedIndex]
+  );
 
   const handleDropBlock = useCallback(
     (targetIndex: number) => {
@@ -294,6 +313,20 @@ export const OutlinerTree: React.FC<OutlinerTreeProps> = ({
         setDragOverIndex(null);
         return;
       }
+      const parentLevel = Math.max(0, blocks[draggedIndex]?.level || 0);
+      let count = 1;
+      for (let i = draggedIndex + 1; i < blocks.length; i++) {
+        if (Math.max(0, blocks[i].level || 0) > parentLevel) {
+          count++;
+        } else {
+          break;
+        }
+      }
+      if (targetIndex >= draggedIndex && targetIndex < draggedIndex + count) {
+        setDraggedIndex(null);
+        setDragOverIndex(null);
+        return;
+      }
       const movingBlock = blocks[draggedIndex];
       if (movingBlock) {
         onMoveBlock(movingBlock.id, targetIndex, movingBlock.level);
@@ -372,7 +405,18 @@ export const OutlinerTree: React.FC<OutlinerTreeProps> = ({
       })}
 
       {canEdit && (
-        <div className="pt-2 pl-2">
+        <div
+          className={`pt-2 pl-2 transition-colors ${
+            dragOverIndex === blocks.length ? 'border-t-2 border-accent bg-accent/10 rounded' : ''
+          }`}
+          onDragOver={(e) => {
+            e.preventDefault();
+            if (draggedIndex !== null) {
+              setDragOverIndex(blocks.length);
+            }
+          }}
+          onDrop={() => handleDropBlock(blocks.length)}
+        >
           <button
             type="button"
             onClick={() => {