Fix duplicate catalog pages from import race condition

A concurrent import could create the same catalog sub-page twice
(getOrCreateCategoryPage / getOrCreateImportedParentPage do a
SELECT-then-INSERT with no unique constraint). Deduplicate right after
insert by keeping the lowest-id page and removing the duplicate, while
never deleting a page that already received catalog items.

src/lib/services/furni-import.ts

@@ -126,6 +126,29 @@ export function buildItemsBaseEnrichmentUpdate(params: {
     `;
 }
 
+/** Keep the lowest-id row for a catalog page and delete any duplicate created
+ * concurrently by a racing import. Returns the surviving page id. */
+async function dedupeCatalogPage(
+	captionSave: string,
+	parentId: number,
+	justCreatedId: number,
+): Promise<number> {
+	const [rows] = (await db.execute(sql`
+    SELECT MIN(id) AS id FROM catalog_pages
+    WHERE caption_save = ${captionSave} AND parent_id = ${parentId}
+  `)) as unknown as [Array<{ id: number }>, unknown];
+	const winner = rows[0]?.id ?? justCreatedId;
+	if (winner !== justCreatedId) {
+		// Never delete a page that already received catalog items.
+		await db.execute(sql`
+      DELETE FROM catalog_pages
+      WHERE id = ${justCreatedId}
+        AND NOT EXISTS (SELECT 1 FROM catalog_items WHERE page_id = ${justCreatedId})
+    `);
+	}
+	return winner;
+}
+
 /** Get or create the root "Imported Furniture" parent page (no items directly on this page).
  * Caches the page ID in-memory for the process lifetime to avoid redundant DB reads
  * during batch imports */
@@ -158,8 +181,12 @@ export async function getOrCreateImportedParentPage(): Promise<number> {
 			'Failed to create "Imported Furniture" parent catalog page',
 		);
 	}
-	parentIdCache = created.id;
-	return created.id;
+	parentIdCache = await dedupeCatalogPage(
+		IMPORTED_PAGE_CAPTION_SAVE,
+		-1,
+		created.id,
+	);
+	return parentIdCache;
 }
 
 /** Determine the catalog category for a furniture item based on its classname and type. */
@@ -246,8 +273,9 @@ export async function getOrCreateCategoryPage(
 		);
 	}
 	if (!categoryPageCache) categoryPageCache = new Map();
-	categoryPageCache.set(captionSave, created.id);
-	return created.id;
+	const winner = await dedupeCatalogPage(captionSave, parentId, created.id);
+	categoryPageCache.set(captionSave, winner);
+	return winner;
 }
 
 export function resetCatalogPageCache(): void {