feat: Refactor tag interaction handling to use unified handlers

frontend/src/documents/interactions/useWorkspaceDragDrop.ts

@@ -1,6 +1,9 @@
 import { useEffect } from 'react';
 import type { MutableRefObject } from 'react';
-import { isTagTransferEvent } from '../features/tagging/tagTransfer';
+import {
+    isTagTransferEvent,
+    getActiveDragState,
+} from '../features/tagging/tagTransfer';
 
 interface UseWorkspaceDragDropArgs {
     shellRef: MutableRefObject<HTMLElement | null>;
@@ -16,21 +19,58 @@ const useWorkspaceDragDrop = ({
             return;
         }
 
-        // Allow drop on workspace
+        // Allow drop on workspace (global app shell)
         const handleTagDragOver = (event: DragEvent) => {
             if (!isTagTransferEvent(event)) {
                 return;
             }
 
-            event.preventDefault();
-            if (event.dataTransfer) event.dataTransfer.dropEffect = 'move';
+            const { sourceDocId } = getActiveDragState();
+
+            // Only allow "Move" (removal) if the tag came from a document
+            if (sourceDocId) {
+                event.preventDefault(); // Necessary to allow dropping
+                if (event.dataTransfer) {
+                    event.dataTransfer.dropEffect = 'move';
+                }
+            }
+        };
+
+        const handleTagDragEnter = (event: DragEvent) => {
+            if (!isTagTransferEvent(event)) {
+                return;
+            }
+            const { sourceDocId } = getActiveDragState();
+            if (sourceDocId) {
+                event.preventDefault();
+                if (event.dataTransfer) {
+                    event.dataTransfer.dropEffect = 'move';
+                }
+            }
+        };
+
+        const handleTagDrop = (event: DragEvent) => {
+            if (!isTagTransferEvent(event)) {
+                return;
+            }
+
+            const { sourceDocId } = getActiveDragState();
+
+            if (sourceDocId) {
+                // Consume the event so the browser reports 'move' back to the source
+                event.preventDefault();
+            }
         };
 
         // Use bubbling (false) so children can stopPropagation
+        host.addEventListener('dragenter', handleTagDragEnter, false);
         host.addEventListener('dragover', handleTagDragOver, false);
+        host.addEventListener('drop', handleTagDrop, false);
 
         return () => {
+            host.removeEventListener('dragenter', handleTagDragEnter, false);
             host.removeEventListener('dragover', handleTagDragOver, false);
+            host.removeEventListener('drop', handleTagDrop, false);
         };
     }, [shellRef]);