Gate article detail on a store-backed cache so the view paints once.

Sku page loads/caches the article before mounting ArticleView; the view reads sync from StorageManager instead of fetching again.

src/api/StorageManager.js

@@ -1,5 +1,6 @@
 import { requireArray, requireDefined, requireObject } from '../utils/apiShape';
 import { notifyError } from '../utils/notify';
+import { parseCategoryTreeResponse } from '../store/categorySlice';
 import { ApiClient } from './ApiClient';
 
 /**
@@ -73,6 +74,8 @@ export class StorageManager extends ApiClient {
   #events = null;
   /** @type {ReturnType<typeof createCache> | null} */
   #articleIndexCache = null;
+  /** @type {Map<string, object>} sku → article detail */
+  #articlesBySku = new Map();
   /** @type {Map<string, Set<() => void>>} sku → refreshers */
   #historyWatchers = new Map();
 
@@ -81,6 +84,52 @@ export class StorageManager extends ApiClient {
     this.#initCaches();
   }
 
+  /** Settled article detail for sku, or undefined. */
+  getArticle(sku) {
+    return this.#articlesBySku.get(String(sku));
+  }
+
+  /** Keep local article detail in sync after GET/PATCH/PUT responses. */
+  setArticle(article) {
+    requireObject(article, 'article');
+    requireDefined(article.sku, 'article.sku');
+    this.#articlesBySku.set(String(article.sku), article);
+    return article;
+  }
+
+  /**
+   * GET /api/article/{sku}, cache detail, return article.
+   * @param {string} sku
+   */
+  async loadArticle(sku) {
+    const res = await this.article.get(sku);
+    requireObject(res, 'GET /api/article/:sku');
+    requireObject(res.article, 'article');
+    return this.setArticle(res.article);
+  }
+
+  /**
+   * Parsed category map + root id from settled caches, or null if any piece missing.
+   * @returns {{ categories: object, rootCategoryId: unknown } | null}
+   */
+  getCategoryState() {
+    const treeData = this.categoryTree;
+    const companies = this.companies;
+    const session = this.authMe;
+    if (treeData == null || companies == null || session == null) return null;
+
+    const companyId = session.user?.selectedCompanyId;
+    if (companyId == null) return null;
+    const company = companies.find((c) => c.id === companyId);
+    if (company == null) return null;
+
+    const parsed = parseCategoryTreeResponse(treeData, company.rootCategoryId);
+    return {
+      categories: parsed.categories,
+      rootCategoryId: parsed.rootCategoryId,
+    };
+  }
+
   /**
    * Fetch article history, then refetch whenever SSE emits `article-<sku>`.
    * @param {string} sku