Refactor: improve code quality and worker flow

Frontend/src/components/shell/ProjectSelector/ProjectSelector.tsx

@@ -103,6 +103,9 @@ const buildProjectTree = (
 	items: readonly ProjectItem[],
 	folders: readonly PersistedProjectFolderRecord[] = [],
 ): ProjectTreeNode[] => [
+	// The selector still presents scaffold project leaves beside persisted folders.
+	// Keep that mixed root shape explicit here so the drag/drop logic can account
+	// for folder-only ordering when we persist sibling positions.
 	...items.map((item) => ({
 		kind: "project" as const,
 		item,
@@ -110,6 +113,11 @@ const buildProjectTree = (
 	...buildPersistedFolderNodes(folders),
 ];
 
+const countProjectFolderSiblingsBeforeIndex = (
+	siblings: readonly ProjectTreeNode[],
+	index: number,
+): number => siblings.slice(0, index).filter((node) => node.kind === "folder").length;
+
 const readPersistedFolders = (body: ProjectFoldersResponse): PersistedProjectFolderRecord[] =>
 	Array.isArray(body.data?.folders) ? body.data.folders : [];
 
@@ -596,10 +604,11 @@ export const ProjectSelector = (props: ProjectSelectorProps): JSX.Element => {
 					? persistedParentLocation.node.children
 					: []
 				: previewNodes;
+			// The preview tree includes project leaves and folders, but the backend only
+			// stores sibling order for folders. Persist a folder-only index so the server
+			// can reapply the same position against the authoritative ordered tree.
 			const targetIndex = previewLocation
-				? previewSiblings
-					.slice(0, previewLocation.index)
-					.filter((node) => node.kind === "folder").length
+				? countProjectFolderSiblingsBeforeIndex(previewSiblings, previewLocation.index)
 				: 0;
 
 			if (
@@ -795,12 +804,12 @@ export const ProjectSelector = (props: ProjectSelectorProps): JSX.Element => {
 	const movePersistedFolder = async (
 		folderPath: string,
 		parentFolderPath: string | null,
-		folderNodeId: string,
-		parentNodeId: string | null,
+		folderStableId: string,
+		parentStableId: string | null,
 		targetIndex: number,
 	): Promise<void> => {
 		const projectId = selectedProject().id;
-		if (!folderPath || !folderNodeId || !isUuidString(projectId)) {
+		if (!folderPath || !folderStableId || !isUuidString(projectId)) {
 			return;
 		}
 
@@ -813,9 +822,9 @@ export const ProjectSelector = (props: ProjectSelectorProps): JSX.Element => {
 				},
 				body: JSON.stringify({
 					folderId: folderPath,
-					folderNodeId,
+					folderNodeId: folderStableId,
 					parentFolderId: parentFolderPath,
-					parentNodeId,
+					parentNodeId: parentStableId,
 					targetIndex,
 				}),
 			});