fix(ui): in-page browse virtual lists and cover load priority (#783)

* fix(ui): in-page browse virtual lists and cover load priority

Align virtualizer scrollMargin with the in-page scroll viewport so
artist/album rows do not vanish on deep scroll after #731. Resolve
CachedImage IntersectionObserver root to the nearest scrolling pane so
network fetch slots favor visible covers; throttle Artists infinite scroll
to one page per visibleCount update.

* chore(release): CHANGELOG and credits for PR #783

src/utils/ui/resolveIntersectionScrollRoot.test.ts

@@ -0,0 +1,44 @@
+// @vitest-environment jsdom
+import { describe, expect, it, beforeEach } from 'vitest';
+import { APP_MAIN_SCROLL_VIEWPORT_ID } from '../../constants/appScroll';
+import { resolveIntersectionScrollRoot } from './resolveIntersectionScrollRoot';
+
+describe('resolveIntersectionScrollRoot', () => {
+  beforeEach(() => {
+    document.body.innerHTML = '';
+  });
+
+  it('prefers the nearest scrolling ancestor', () => {
+    const outer = document.createElement('div');
+    const scroller = document.createElement('div');
+    const img = document.createElement('img');
+    Object.defineProperty(scroller, 'scrollHeight', { value: 2000, configurable: true });
+    Object.defineProperty(scroller, 'clientHeight', { value: 400, configurable: true });
+    scroller.style.overflowY = 'auto';
+    outer.appendChild(scroller);
+    scroller.appendChild(img);
+    document.body.appendChild(outer);
+
+    expect(resolveIntersectionScrollRoot(img)).toBe(scroller);
+  });
+
+  it('falls back to mainstage in-page viewport class', () => {
+    const inpage = document.createElement('div');
+    inpage.className = 'mainstage-inpage-scroll__viewport';
+    const img = document.createElement('img');
+    inpage.appendChild(img);
+    document.body.appendChild(inpage);
+
+    expect(resolveIntersectionScrollRoot(img)).toBe(inpage);
+  });
+
+  it('falls back to app main scroll viewport id', () => {
+    const main = document.createElement('div');
+    main.id = APP_MAIN_SCROLL_VIEWPORT_ID;
+    const img = document.createElement('img');
+    main.appendChild(img);
+    document.body.appendChild(main);
+
+    expect(resolveIntersectionScrollRoot(img)).toBe(main);
+  });
+});

src/utils/ui/resolveIntersectionScrollRoot.ts

@@ -0,0 +1,25 @@
+import { APP_MAIN_SCROLL_VIEWPORT_ID } from '../../constants/appScroll';
+
+/**
+ * Scroll container for `IntersectionObserver` priority scoring on cover art.
+ * Prefer the nearest scrolling ancestor (in-page browse, queue, route viewport);
+ * fall back to known viewport class hooks, then the main route scroll element.
+ */
+export function resolveIntersectionScrollRoot(node: HTMLElement): Element | null {
+  let parent = node.parentElement;
+  while (parent) {
+    const { overflowY } = window.getComputedStyle(parent);
+    if (
+      (overflowY === 'auto' || overflowY === 'scroll' || overflowY === 'overlay')
+      && parent.scrollHeight > parent.clientHeight + 2
+    ) {
+      return parent;
+    }
+    parent = parent.parentElement;
+  }
+  return (
+    (node.closest('.mainstage-inpage-scroll__viewport') as HTMLElement | null)
+    ?? (node.closest('.app-shell-route-scroll__viewport') as HTMLElement | null)
+    ?? (document.getElementById(APP_MAIN_SCROLL_VIEWPORT_ID) as HTMLElement | null)
+  );
+}