fix(feed): measure expanded reply media height

src/lib/utils/__tests__/pretext-height-estimates.test.ts

@@ -7,6 +7,7 @@ import {
   resolveFeedVirtualizationMode,
   resolveReplyVirtualizationMode,
 } from '../pretext-height-estimates';
+import { EXPANDED_MEDIA_DATA_ATTRIBUTE } from '../measurement-attributes';
 
 describe('pretext-height-estimates', () => {
   beforeEach(() => {
@@ -81,6 +82,18 @@ describe('pretext-height-estimates', () => {
     expect(getReplyItemSizeFromElement(element, 'offsetHeight')).toBe(222);
   });
 
+  it('uses live DOM height when expanded media is inside an estimated item', () => {
+    const element = document.createElement('div');
+    const child = document.createElement('div');
+
+    Object.defineProperty(element, 'offsetHeight', { configurable: true, value: 421 });
+    element.dataset.pretextHeight = '123';
+    child.setAttribute(EXPANDED_MEDIA_DATA_ATTRIBUTE, 'true');
+    element.appendChild(child);
+
+    expect(getReplyItemSizeFromElement(element, 'offsetHeight')).toBe(421);
+  });
+
   it('adds desktop board-label height for multiboard text posts without media', () => {
     const metrics = {
       abbrFontSizePx: 13,

src/lib/utils/measurement-attributes.ts

@@ -0,0 +1 @@
+export const EXPANDED_MEDIA_DATA_ATTRIBUTE = 'data-expanded-media';

src/lib/utils/pretext-height-estimates.ts

@@ -1,6 +1,7 @@
 import type { Comment } from '@bitsocial/bitsocial-react-hooks';
 import { layout, layoutNextLine, prepare, prepareWithSegments } from '@chenglou/pretext';
 import { getCommentMediaInfo, getHasThumbnail } from './media-utils';
+import { EXPANDED_MEDIA_DATA_ATTRIBUTE } from './measurement-attributes';
 import { removeMarkdown } from './post-utils';
 import { getRenderableMobileBacklinks } from './reply-backlink-utils';
 
@@ -839,6 +840,10 @@ export const getPretextItemSizeFromElement = (element: HTMLElement, field: 'offs
     return element.offsetWidth;
   }
 
+  if (element.dataset.expandedMedia === 'true' || element.querySelector(`[${EXPANDED_MEDIA_DATA_ATTRIBUTE}="true"]`)) {
+    return element.offsetHeight;
+  }
+
   const ownEstimatedHeight = Number.parseFloat(element.dataset.pretextHeight || '');
   if (Number.isFinite(ownEstimatedHeight) && ownEstimatedHeight > 0) {
     return ownEstimatedHeight;