From 6cb28b0e4f03505a59ade1585ff96d2b1bcf5beb Mon Sep 17 00:00:00 2001
From: Tommaso Casaburi <tom@bitsocial.net>
Date: Sat, 13 Jun 2026 13:39:22 +0700
Subject: [PATCH] fix(youtube thumbnails): prefer best available image

Prefer the best available YouTube thumbnail, fall back cleanly when high-resolution images are unavailable, and keep the React Doctor PR gate scoped to newly introduced issues.
---
 .github/workflows/react-doctor.yml            |  16 +-
 .../__tests__/catalog-row.test.tsx            |   2 +-
 src/components/catalog-row/catalog-row.tsx    |  37 +++-
 .../__tests__/comment-media.test.tsx          |  46 +++-
 .../comment-media/comment-media.tsx           |  16 +-
 .../markdown/__tests__/markdown.test.tsx      |   2 +-
 .../post-form/__tests__/post-form.test.tsx    |  63 +++++-
 src/components/post-form/post-form.tsx        | 208 +++++++++---------
 .../__tests__/reply-modal.test.tsx            | 131 +++++++++--
 src/components/reply-modal/reply-modal.tsx    |  85 +++----
 .../use-youtube-thumbnail-fallback.test.tsx   |  64 ++++++
 src/hooks/use-publish-submission-guard.ts     |  26 +++
 src/hooks/use-youtube-thumbnail-fallback.ts   |  48 ++++
 .../use-youtube-thumbnail-link-conversion.ts  |  25 ++-
 src/lib/utils/__tests__/media-utils.test.ts   | 106 ++++++++-
 src/lib/utils/media-utils.ts                  | 137 +++++++++++-
 16 files changed, 813 insertions(+), 199 deletions(-)
 create mode 100644 src/hooks/__tests__/use-youtube-thumbnail-fallback.test.tsx
 create mode 100644 src/hooks/use-publish-submission-guard.ts
 create mode 100644 src/hooks/use-youtube-thumbnail-fallback.ts

diff --git a/.github/workflows/react-doctor.yml b/.github/workflows/react-doctor.yml
index 15dbfed3..b6280129 100644
--- a/.github/workflows/react-doctor.yml
+++ b/.github/workflows/react-doctor.yml
@@ -1,7 +1,7 @@
 # React Doctor PR review.
-# Reports only issues this PR INTRODUCES (diffed against the merge-base) as inline
-# review comments + a sticky summary. It reads doctor.config.jsonc, so the
-# React-Compiler rules we don't enforce stay suppressed (see that file and
+# Reports only issues this PR INTRODUCES (diffed against the base branch) as
+# GitHub annotations. It reads doctor.config.jsonc, so the React-Compiler rules
+# we don't enforce stay suppressed (see that file and
 # docs/agent-playbooks/known-surprises.md). We do NOT chase the aggregate score.
 name: React Doctor
 
@@ -25,4 +25,12 @@ jobs:
       - uses: actions/checkout@v4
         with:
           fetch-depth: 0 # so React Doctor can diff against the merge-base for new-vs-existing
-      - uses: millionco/react-doctor@v1
+      - name: Setup Node.js v22
+        uses: actions/setup-node@v4
+        with:
+          node-version: 22
+      - run: corepack enable
+      - name: Install dependencies
+        run: yarn install --immutable
+      - name: Run React Doctor on changed files
+        run: yarn doctor --verbose --scope changed --base "origin/${{ github.base_ref }}" --annotations --blocking error
diff --git a/src/components/catalog-row/__tests__/catalog-row.test.tsx b/src/components/catalog-row/__tests__/catalog-row.test.tsx
index 5df18c9c..36ad7ed0 100644
--- a/src/components/catalog-row/__tests__/catalog-row.test.tsx
+++ b/src/components/catalog-row/__tests__/catalog-row.test.tsx
@@ -185,7 +185,7 @@ vi.mock('../../../hooks/use-hide', () => ({
   }),
 }));
 
-vi.mock('../../post-desktop/post-menu-desktop', () => ({
+vi.mock('../../post-desktop/post-menu-desktop/post-menu-desktop', () => ({
   default: ({ postMenu }: { postMenu: { cid?: string } }) => createElement('span', { 'data-testid': `post-menu-${postMenu.cid}` }, 'menu'),
 }));
 
diff --git a/src/components/catalog-row/catalog-row.tsx b/src/components/catalog-row/catalog-row.tsx
index c9ba79b1..0a08c294 100644
--- a/src/components/catalog-row/catalog-row.tsx
+++ b/src/components/catalog-row/catalog-row.tsx
@@ -1,4 +1,4 @@
-import { memo, useEffect, useMemo, useRef, useState } from 'react';
+import { memo, type SyntheticEvent, useEffect, useMemo, useRef, useState } from 'react';
 import { createPortal } from 'react-dom';
 import { useTranslation } from 'react-i18next';
 import { Link, useLocation, useParams } from 'react-router-dom';
@@ -16,10 +16,11 @@ import useEditCommentPrivileges from '../../hooks/use-author-privileges';
 import { useCommentMediaInfo } from '../../hooks/use-comment-media-info';
 import useCountLinksInReplies from '../../hooks/use-count-links-in-replies';
 import useFetchGifFirstFrame from '../../hooks/use-fetch-gif-first-frame';
+import { useYouTubeThumbnailFallback } from '../../hooks/use-youtube-thumbnail-fallback';
 import useHide from '../../hooks/use-hide';
 import { isCommentArchived } from '../../lib/utils/comment-moderation-utils';
 import { CATALOG_PREVIEW_MARKDOWN_OPTIONS, removeMarkdown } from '../../lib/utils/post-utils';
-import PostMenuDesktop from '../post-desktop/post-menu-desktop';
+import PostMenuDesktop from '../post-desktop/post-menu-desktop/post-menu-desktop';
 import styles from './catalog-row.module.css';
 import capitalize from 'lodash/capitalize';
 import { selectPostMenuProps } from '../../lib/utils/post-menu-props';
@@ -39,11 +40,31 @@ export const CatalogPostMedia = ({ cid, commentMediaInfo, linkWidth, linkHeight,
   void cid;
   const { patternThumbnailUrl, thumbnail, type, url } = commentMediaInfo || {};
   const iframeThumbnail = patternThumbnailUrl || thumbnail;
+  const {
+    handleThumbnailError: handleIframeThumbnailError,
+    handleThumbnailLoad: handleIframeThumbnailLoad,
+    isUnavailable: isIframeThumbnailUnavailable,
+    thumbnailUrl: resolvedIframeThumbnail,
+  } = useYouTubeThumbnailFallback(iframeThumbnail);
   const { frameUrl: gifFrameUrl, status: gifFrameStatus } = useFetchGifFirstFrame(type === 'gif' ? url : undefined);
   const [isLoaded, setIsLoaded] = useState(false);
   const [hasError, setHasError] = useState(false);
   const handleLoad = () => setIsLoaded(true);
   const handleError = () => setHasError(true);
+  const handleIframeLoad = (event: SyntheticEvent<HTMLImageElement>) => {
+    if (handleIframeThumbnailLoad(event.currentTarget)) {
+      return;
+    }
+
+    handleLoad();
+  };
+  const handleIframeError = () => {
+    if (handleIframeThumbnailError()) {
+      return;
+    }
+
+    handleError();
+  };
   const loadingStyle = { opacity: isLoaded ? 1 : 0 };
 
   const { imageSize } = useCatalogStyleStore();
@@ -96,22 +117,24 @@ export const CatalogPostMedia = ({ cid, commentMediaInfo, linkWidth, linkHeight,
     );
   } else if (type === 'webpage' && !hasError) {
     thumbnailComponent = <img src={thumbnail} alt='' onLoad={handleLoad} onError={handleError} style={loadingStyle} width={numericWidth} height={numericHeight} />;
-  } else if (type === 'iframe' && iframeThumbnail && !hasError) {
-    thumbnailComponent = <img src={iframeThumbnail} alt='' onLoad={handleLoad} onError={handleError} style={loadingStyle} width={numericWidth} height={numericHeight} />;
+  } else if (type === 'iframe' && resolvedIframeThumbnail && !hasError) {
+    thumbnailComponent = (
+      <img src={resolvedIframeThumbnail} alt='' onLoad={handleIframeLoad} onError={handleIframeError} style={loadingStyle} width={numericWidth} height={numericHeight} />
+    );
   } else if (type === 'audio') {
     thumbnailComponent = <audio src={url} aria-label='Audio preview' controls />;
   }
 
   return (
     <div
-      className={hasError ? '' : styles.mediaWrapper}
+      className={hasError || isIframeThumbnailUnavailable ? '' : styles.mediaWrapper}
       style={{
         ...CSSProperties,
         ...(matchedFilterColor ? { border: `3px solid ${matchedFilterColor}` } : {}),
       }}
     >
-      {!isLoaded && !hasError && type !== 'video' && type !== 'audio' && <span className={styles.loadingSkeleton} />}
-      {hasError ? <img className={styles.fileDeleted} src='assets/filedeleted-res.gif' alt='' /> : thumbnailComponent}
+      {!isLoaded && !hasError && !isIframeThumbnailUnavailable && type !== 'video' && type !== 'audio' && <span className={styles.loadingSkeleton} />}
+      {hasError || isIframeThumbnailUnavailable ? <img className={styles.fileDeleted} src='assets/filedeleted-res.gif' alt='' /> : thumbnailComponent}
     </div>
   );
 };
diff --git a/src/components/comment-media/__tests__/comment-media.test.tsx b/src/components/comment-media/__tests__/comment-media.test.tsx
index fcd73faf..b50f2402 100644
--- a/src/components/comment-media/__tests__/comment-media.test.tsx
+++ b/src/components/comment-media/__tests__/comment-media.test.tsx
@@ -29,6 +29,17 @@ vi.mock('../../../lib/utils/media-utils', () => ({
   getDisplayMediaInfoType: (type: string) => type,
   getHasThumbnail: () => testState.getHasThumbnailResult,
   getMediaDimensions: () => '640x480',
+  getYouTubeThumbnailFallbackUrls: (thumbnailUrl?: string) => {
+    if (!thumbnailUrl?.includes('img.youtube.com/vi/')) return thumbnailUrl ? [thumbnailUrl] : [];
+    const videoId = thumbnailUrl.split('/vi/')[1]?.split('/')[0];
+    return [
+      `https://img.youtube.com/vi/${videoId}/maxresdefault.jpg`,
+      `https://img.youtube.com/vi/${videoId}/sddefault.jpg`,
+      `https://img.youtube.com/vi/${videoId}/mqdefault.jpg`,
+      `https://img.youtube.com/vi/${videoId}/hqdefault.jpg`,
+    ];
+  },
+  isMissingYouTubeThumbnailImage: (thumbnailUrl: string, width: number, height: number) => thumbnailUrl.includes('img.youtube.com/vi/') && width === 120 && height === 90,
 }));
 
 vi.mock('../../../lib/utils/url-utils', () => ({
@@ -64,12 +75,15 @@ vi.mock('../../../hooks/use-is-mobile', () => ({
   default: () => testState.isMobile,
 }));
 
-vi.mock('../../embed', () => ({
+vi.mock('../../embed/embed', () => ({
   __esModule: true,
-  canEmbed: () => testState.canEmbed,
   default: ({ url }: { url: string }) => createElement('div', { 'data-testid': 'embed' }, url),
 }));
 
+vi.mock('../../embed/embed-utils', () => ({
+  canEmbed: () => testState.canEmbed,
+}));
+
 vi.mock('@ruffle-rs/ruffle', () => ({}));
 
 let container: HTMLDivElement;
@@ -298,7 +312,7 @@ describe('CommentMedia', () => {
   it('renders a youtube thumbnail before the embed is opened', async () => {
     await renderMedia({
       commentMediaInfo: {
-        patternThumbnailUrl: 'https://img.youtube.com/vi/abc123/0.jpg',
+        patternThumbnailUrl: 'https://img.youtube.com/vi/abc123/maxresdefault.jpg',
         type: 'iframe',
         url: 'https://www.youtube.com/watch?v=abc123',
       },
@@ -306,10 +320,34 @@ describe('CommentMedia', () => {
       showThumbnail: true,
     });
 
-    expect(container.querySelector('img[src="https://img.youtube.com/vi/abc123/0.jpg"]')).toBeTruthy();
+    expect(container.querySelector('img[src="https://img.youtube.com/vi/abc123/maxresdefault.jpg"]')).toBeTruthy();
     expect(container.querySelector('[data-testid="embed"]')).toBeNull();
   });
 
+  it('falls back when youtube serves the missing-thumbnail placeholder as a loaded image', async () => {
+    await renderMedia({
+      commentMediaInfo: {
+        patternThumbnailUrl: 'https://img.youtube.com/vi/missing-max/maxresdefault.jpg',
+        type: 'iframe',
+        url: 'https://www.youtube.com/watch?v=missing-max',
+      },
+      setShowThumbnail: setShowThumbnailMock,
+      showThumbnail: true,
+    });
+
+    const image = container.querySelector<HTMLImageElement>('img[src="https://img.youtube.com/vi/missing-max/maxresdefault.jpg"]');
+    expect(image).toBeTruthy();
+    if (!image) throw new Error('Expected youtube thumbnail image to render');
+
+    Object.defineProperty(image, 'naturalWidth', { configurable: true, value: 120 });
+    Object.defineProperty(image, 'naturalHeight', { configurable: true, value: 90 });
+    await act(async () => {
+      image.dispatchEvent(new Event('load', { bubbles: true }));
+    });
+
+    expect(container.querySelector('img[src="https://img.youtube.com/vi/missing-max/sddefault.jpg"]')).toBeTruthy();
+  });
+
   it('renders the expanded embed view with a close button on mobile', async () => {
     testState.isMobile = true;
 
diff --git a/src/components/comment-media/comment-media.tsx b/src/components/comment-media/comment-media.tsx
index 0c9db5fc..1c837901 100644
--- a/src/components/comment-media/comment-media.tsx
+++ b/src/components/comment-media/comment-media.tsx
@@ -5,8 +5,10 @@ import { getHostname, parseHttpUrl } from '../../lib/utils/url-utils';
 import useExpandedMediaStore from '../../stores/use-expanded-media-store';
 import useFetchGifFirstFrame from '../../hooks/use-fetch-gif-first-frame';
 import useIsMobile from '../../hooks/use-is-mobile';
+import { useYouTubeThumbnailFallback } from '../../hooks/use-youtube-thumbnail-fallback';
 import styles from './comment-media.module.css';
-import Embed, { canEmbed } from '../embed';
+import Embed from '../embed/embed';
+import { canEmbed } from '../embed/embed-utils';
 import RufflePlayer from './ruffle-player';
 
 interface MediaProps {
@@ -108,8 +110,14 @@ const Thumbnail = ({
   let thumbnailComponent: React.ReactNode = null;
   const thumbnailDimensions = { '--width': displayWidth, '--height': displayHeight } as React.CSSProperties;
   const iframeThumbnail = patternThumbnailUrl || thumbnail;
+  const {
+    handleThumbnailError: handleIframeThumbnailError,
+    handleThumbnailLoad: handleIframeThumbnailLoad,
+    isUnavailable: isIframeThumbnailUnavailable,
+    thumbnailUrl: resolvedIframeThumbnail,
+  } = useYouTubeThumbnailFallback(iframeThumbnail);
   const { frameUrl: gifFrameUrl, status: gifFrameStatus } = gifFrameState;
-  const hasThumbnail = getHasThumbnail(commentMediaInfo, url);
+  const hasThumbnail = getHasThumbnail(commentMediaInfo, url) && !isIframeThumbnailUnavailable;
   const handleOpenMedia = () => setShowThumbnail(false);
 
   if (type === 'gif') {
@@ -137,9 +145,9 @@ const Thumbnail = ({
       </button>
     );
   } else if (type === 'iframe') {
-    thumbnailComponent = iframeThumbnail ? (
+    thumbnailComponent = resolvedIframeThumbnail ? (
       <button type='button' className={styles.mediaToggleButton} aria-label='Open embedded media preview' onClick={handleOpenMedia}>
-        <img src={iframeThumbnail} alt='' />
+        <img src={resolvedIframeThumbnail} alt='' onLoad={(event) => handleIframeThumbnailLoad(event.currentTarget)} onError={() => handleIframeThumbnailError()} />
       </button>
     ) : null;
   } else if (type === 'audio') {
diff --git a/src/components/markdown/__tests__/markdown.test.tsx b/src/components/markdown/__tests__/markdown.test.tsx
index c5a67cb7..50613e7d 100644
--- a/src/components/markdown/__tests__/markdown.test.tsx
+++ b/src/components/markdown/__tests__/markdown.test.tsx
@@ -643,7 +643,7 @@ describe('Markdown', () => {
     testState.embeddableHosts = new Set(['www.youtube.com']);
     testState.mediaInfoByHref = {
       'https://www.youtube.com/watch?v=abc123': {
-        patternThumbnailUrl: 'https://img.youtube.com/vi/abc123/0.jpg',
+        patternThumbnailUrl: 'https://img.youtube.com/vi/abc123/maxresdefault.jpg',
         type: 'iframe',
         url: 'https://www.youtube.com/watch?v=abc123',
       },
diff --git a/src/components/post-form/__tests__/post-form.test.tsx b/src/components/post-form/__tests__/post-form.test.tsx
index 38e46a89..020d0c81 100644
--- a/src/components/post-form/__tests__/post-form.test.tsx
+++ b/src/components/post-form/__tests__/post-form.test.tsx
@@ -16,6 +16,7 @@ const testState = vi.hoisted(() => ({
     subscriptions: ['music-posting.eth'],
   },
   accountComment: undefined as { communityAddress?: string } | undefined,
+  bestAvailableYouTubeThumbnailMock: undefined as undefined | ((link: string) => Promise<string | undefined>),
   accountCommunityAddresses: ['mod.eth'] as string[],
   comments: {} as Record<string, { commentModeration?: { archived?: boolean }; deleted?: boolean; locked?: boolean; postCid?: string; removed?: boolean }>,
   directories: [
@@ -354,7 +355,7 @@ vi.mock('../../../lib/utils/media-utils', () => {
         return { type: 'audio', url: link };
       }
       if (link.includes('youtube.com')) {
-        return { patternThumbnailUrl: 'https://img.youtube.com/vi/abc123/0.jpg', type: 'iframe', url: link };
+        return { patternThumbnailUrl: 'https://img.youtube.com/vi/abc123/maxresdefault.jpg', type: 'iframe', url: link };
       }
       return { type: 'webpage', url: link };
     },
@@ -364,7 +365,21 @@ vi.mock('../../../lib/utils/media-utils', () => {
         const url = new URL(link);
         if (!url.hostname.includes('youtube.com')) return undefined;
         const videoId = url.searchParams.get('v');
-        return videoId ? `https://img.youtube.com/vi/${videoId}/0.jpg` : undefined;
+        return videoId ? `https://img.youtube.com/vi/${videoId}/maxresdefault.jpg` : undefined;
+      } catch {
+        return undefined;
+      }
+    },
+    getBestAvailableYouTubeThumbnailUrlFromLink: async (link: string) => {
+      if (testState.bestAvailableYouTubeThumbnailMock) {
+        return testState.bestAvailableYouTubeThumbnailMock(link);
+      }
+
+      try {
+        const url = new URL(link);
+        if (!url.hostname.includes('youtube.com')) return undefined;
+        const videoId = url.searchParams.get('v');
+        return videoId ? `https://img.youtube.com/vi/${videoId}/maxresdefault.jpg` : undefined;
       } catch {
         return undefined;
       }
@@ -516,6 +531,7 @@ describe('PostForm', () => {
       subscriptions: ['music-posting.eth'],
     };
     testState.accountComment = undefined;
+    testState.bestAvailableYouTubeThumbnailMock = undefined;
     testState.accountCommunityAddresses = ['mod.eth'];
     testState.comments = {};
     testState.directories = [
@@ -689,7 +705,7 @@ describe('PostForm', () => {
 
   it('converts YouTube links to thumbnail file links on media-only post forms', async () => {
     const youtubeLink = 'https://www.youtube.com/watch?v=abc123';
-    const thumbnailLink = 'https://img.youtube.com/vi/abc123/0.jpg';
+    const thumbnailLink = 'https://img.youtube.com/vi/abc123/maxresdefault.jpg';
 
     await renderPostForm('/all');
     await clickByText(container, 'start_new_thread');
@@ -749,6 +765,47 @@ describe('PostForm', () => {
     expect(testState.publishedPostOptions?.content).toBe(youtubeLink);
   });
 
+  it('ignores duplicate post clicks while youtube thumbnail resolution is pending', async () => {
+    const youtubeLink = 'https://www.youtube.com/watch?v=slow123';
+    const thumbnailLink = 'https://img.youtube.com/vi/slow123/maxresdefault.jpg';
+    let resolveThumbnail: (thumbnailLink: string) => void = () => {};
+    const thumbnailPromise = new Promise<string | undefined>((resolve) => {
+      resolveThumbnail = resolve;
+    });
+    const resolverMock = vi.fn(() => thumbnailPromise);
+    testState.bestAvailableYouTubeThumbnailMock = resolverMock;
+
+    await renderPostForm('/all');
+    await clickByText(container, 'start_new_thread');
+
+    const table = container.querySelector('table') as HTMLTableElement;
+    const select = table.querySelector('select') as HTMLSelectElement;
+    const textarea = table.querySelector('textarea') as HTMLTextAreaElement;
+    const linkInput = table.querySelectorAll<HTMLInputElement>('input[type="text"]')[3];
+    const postButton = Array.from(table.querySelectorAll('button')).find((button) => button.textContent === 'post') as HTMLButtonElement;
+
+    await dispatchChange(select, 'music-posting.eth');
+    await dispatchInput(textarea, 'Video body');
+    await dispatchInput(linkInput, youtubeLink);
+
+    await clickByText(table, 'post');
+    expect(postButton.disabled).toBe(true);
+
+    await clickByText(table, 'post');
+    expect(resolverMock).toHaveBeenCalledTimes(1);
+    expect(testState.publishPostMock).not.toHaveBeenCalled();
+
+    await act(async () => {
+      resolveThumbnail(thumbnailLink);
+      await thumbnailPromise;
+      await Promise.resolve();
+    });
+
+    expect(testState.publishPostMock).toHaveBeenCalledTimes(1);
+    expect(testState.publishedPostOptions?.link).toBe(thumbnailLink);
+    expect(testState.publishedPostOptions?.content).toBe(`${youtubeLink}\nVideo body`);
+  });
+
   it('publishes known twimg query-format post links with a path extension without editing the field', async () => {
     const twimgLink = 'https://pbs.twimg.com/media/HJxnhNKWMAAhqFU?format=jpg&name=medium';
     const publishLink = 'https://pbs.twimg.com/media/HJxnhNKWMAAhqFU.jpg';
diff --git a/src/components/post-form/post-form.tsx b/src/components/post-form/post-form.tsx
index 6b59600b..8209bc10 100644
--- a/src/components/post-form/post-form.tsx
+++ b/src/components/post-form/post-form.tsx
@@ -44,6 +44,7 @@ import { useResolvedCommunityAddress } from '../../hooks/use-resolved-community-
 import useSafeAccountComment from '../../hooks/use-safe-account-comment';
 import useFetchGifFirstFrame from '../../hooks/use-fetch-gif-first-frame';
 import { useYouTubeThumbnailLinkConversion } from '../../hooks/use-youtube-thumbnail-link-conversion';
+import usePublishSubmissionGuard from '../../hooks/use-publish-submission-guard';
 import usePublishPost from '../../hooks/use-publish-post';
 import usePublishReply from '../../hooks/use-publish-reply';
 import { useFileUpload } from '../../hooks/use-file-upload';
@@ -104,6 +105,7 @@ const PostFormActions = ({
   onPublishReply,
   onPublishPost,
   handleUpload,
+  isPublishSubmissionInFlight,
   isUploading,
   showUploadControls,
 }: {
@@ -111,22 +113,23 @@ const PostFormActions = ({
   variant: 'reply' | 'post' | 'upload';
   t: TFunction;
   isInPostView: boolean;
-  onPublishReply: () => void;
-  onPublishPost: () => void;
+  onPublishReply: () => void | Promise<void>;
+  onPublishPost: () => void | Promise<void>;
   handleUpload: () => void;
+  isPublishSubmissionInFlight: boolean;
   isUploading: boolean;
   showUploadControls: boolean;
 }) => {
   if (variant === 'reply' && isInPostView) {
     return (
-      <button type='button' onClick={onPublishReply} disabled={disableReplyPublish || isUploading}>
+      <button type='button' onClick={onPublishReply} disabled={disableReplyPublish || isPublishSubmissionInFlight || isUploading}>
         {t('post')}
       </button>
     );
   }
   if (variant === 'post' && !isInPostView) {
     return (
-      <button type='button' onClick={onPublishPost}>
+      <button type='button' onClick={onPublishPost} disabled={isPublishSubmissionInFlight}>
         {t('post')}
       </button>
     );
@@ -186,11 +189,12 @@ interface PostFormFieldsProps {
   showMathTagsPrompt: boolean;
   showBbcodeToolbar: boolean;
   onBbcodePreviewToggle: () => void;
-  onPublishReply: () => void;
-  onPublishPost: () => void;
+  onPublishReply: () => void | Promise<void>;
+  onPublishPost: () => void | Promise<void>;
   handleUpload: () => void;
   uploadFile: ReturnType<typeof useFileUpload>['uploadFile'];
   onOekakiClearUploadedUrl: (url: string) => void;
+  isPublishSubmissionInFlight: boolean;
   disableReplyPublish: boolean;
 }
 
@@ -244,6 +248,7 @@ const PostFormFields = ({
   handleUpload,
   uploadFile,
   onOekakiClearUploadedUrl,
+  isPublishSubmissionInFlight,
   disableReplyPublish,
 }: PostFormFieldsProps) => (
   <>
@@ -273,6 +278,7 @@ const PostFormFields = ({
           onPublishPost={onPublishPost}
           handleUpload={handleUpload}
           disableReplyPublish={disableReplyPublish}
+          isPublishSubmissionInFlight={isPublishSubmissionInFlight}
           isUploading={isUploading}
           showUploadControls={showUploadControls}
         />
@@ -304,6 +310,7 @@ const PostFormFields = ({
             onPublishPost={onPublishPost}
             handleUpload={handleUpload}
             disableReplyPublish={disableReplyPublish}
+            isPublishSubmissionInFlight={isPublishSubmissionInFlight}
             isUploading={isUploading}
             showUploadControls={showUploadControls}
           />
@@ -393,6 +400,7 @@ const PostFormFields = ({
             onPublishPost={onPublishPost}
             handleUpload={handleUpload}
             disableReplyPublish={disableReplyPublish}
+            isPublishSubmissionInFlight={isPublishSubmissionInFlight}
             isUploading={isUploading}
             showUploadControls={showUploadControls}
           />
@@ -588,6 +596,7 @@ const PostFormTable = ({ closeForm, postCid }: { closeForm: () => void; postCid:
   const [formError, setFormError] = useState<string | PostOptionsValidationError | null>(null);
   const [isBbcodePreviewing, setIsBbcodePreviewing] = useState(false);
   const [bbcodePreviewContent, setBbcodePreviewContent] = useState('');
+  const { isPublishSubmissionInFlight, runPublishSubmission } = usePublishSubmissionGuard();
 
   const checkContentLength = useRef(
     debounce((content: string, t: TFunction, options: string, directoryCode: string | undefined) => {
@@ -645,66 +654,67 @@ const PostFormTable = ({ closeForm, postCid }: { closeForm: () => void; postCid:
     return params?.boardIdentifier ? `/${params.boardIdentifier}` : null;
   };
 
-  const onPublishPost = () => {
-    const appliedYouTubeConversion = applyPendingConversion();
+  const onPublishPost = () =>
+    runPublishSubmission(async () => {
+      const appliedYouTubeConversion = await applyPendingConversion();
 
-    const currentTitle = subjectRef.current?.value.trim() || '';
-    const currentContent = textRef.current?.value || '';
-    const currentUrl = urlRef.current?.value.trim() || '';
-    const currentOptions = optionsRef.current?.value || '';
-    const currentOptionsError = getPostOptionsValidationError(currentOptions, postOptionsDirectoryCode);
-    const publishContent = getContentWithOptions(currentContent, currentOptions, fortuneEntryRef, diceRollRef, postOptionsDirectoryCode);
+      const currentTitle = subjectRef.current?.value.trim() || '';
+      const currentContent = textRef.current?.value || '';
+      const currentUrl = urlRef.current?.value.trim() || '';
+      const currentOptions = optionsRef.current?.value || '';
+      const currentOptionsError = getPostOptionsValidationError(currentOptions, postOptionsDirectoryCode);
+      const publishContent = getContentWithOptions(currentContent, currentOptions, fortuneEntryRef, diceRollRef, postOptionsDirectoryCode);
 
-    checkContentLength.cancel();
-    checkPostOptions.cancel();
-    setLengthError(null);
-    setFormError(null);
-    nonokoRedirectPathRef.current = null;
+      checkContentLength.cancel();
+      checkPostOptions.cancel();
+      setLengthError(null);
+      setFormError(null);
+      nonokoRedirectPathRef.current = null;
 
-    if (currentOptionsError) {
-      setFormError(currentOptionsError);
-      return;
-    }
+      if (currentOptionsError) {
+        setFormError(currentOptionsError);
+        return;
+      }
 
-    if (!currentTitle && !publishContent.trim() && !currentUrl) {
-      setFormError(`${t('error')}: ${t('empty_comment_alert')}`);
-      return;
-    }
-    if (currentUrl && !isValidPublishURL(currentUrl)) {
-      setFormError(`${t('error')}: ${t('invalid_url_alert')}`);
-      return;
-    }
-    if (currentUrl && requirePostLinkIsMedia && !isPublishFileMediaLink(currentUrl)) {
-      setFormError(`${t('error')}: ${t('link_not_image_or_video_alert')}`);
-      return;
-    }
-    const expiringMediaLinkAlert = currentUrl ? getExpiringMediaLinkAlert(currentUrl, t) : null;
-    if (expiringMediaLinkAlert) {
-      setFormError(expiringMediaLinkAlert);
-      return;
-    }
+      if (!currentTitle && !publishContent.trim() && !currentUrl) {
+        setFormError(`${t('error')}: ${t('empty_comment_alert')}`);
+        return;
+      }
+      if (currentUrl && !isValidPublishURL(currentUrl)) {
+        setFormError(`${t('error')}: ${t('invalid_url_alert')}`);
+        return;
+      }
+      if (currentUrl && requirePostLinkIsMedia && !isPublishFileMediaLink(currentUrl)) {
+        setFormError(`${t('error')}: ${t('link_not_image_or_video_alert')}`);
+        return;
+      }
+      const expiringMediaLinkAlert = currentUrl ? getExpiringMediaLinkAlert(currentUrl, t) : null;
+      if (expiringMediaLinkAlert) {
+        setFormError(expiringMediaLinkAlert);
+        return;
+      }
 
-    if (publishContent.trim().length > 2000) {
-      setFormError(`${t('error')}: ${t('field_too_long')}`);
-      return;
-    }
+      if (publishContent.trim().length > 2000) {
+        setFormError(`${t('error')}: ${t('field_too_long')}`);
+        return;
+      }
 
-    if ((isInAllView || isInSubscriptionsView || isInModView) && !publishPostOptions.communityAddress) {
-      setFormError(`${t('error')}: ${t('no_board_selected_warning')}`);
-      return;
-    }
+      if ((isInAllView || isInSubscriptionsView || isInModView) && !publishPostOptions.communityAddress) {
+        setFormError(`${t('error')}: ${t('no_board_selected_warning')}`);
+        return;
+      }
 
-    const flagPublishOptions = getCommentFlagPublishOptionsForDirectory(directoryEntry, flagRef.current?.value);
-    const flashTagPublishOptions = getFlashTagPublishOptionsForDirectoryCode(postOptionsDirectoryCode, flashTagRef.current?.value);
-    const flairs = mergeFlairs(flagPublishOptions.flairs, flashTagPublishOptions.flairs);
-    const publishOptions = {
-      ...flagPublishOptions,
-      ...(flairs ? { flairs } : {}),
-    };
+      const flagPublishOptions = getCommentFlagPublishOptionsForDirectory(directoryEntry, flagRef.current?.value);
+      const flashTagPublishOptions = getFlashTagPublishOptionsForDirectoryCode(postOptionsDirectoryCode, flashTagRef.current?.value);
+      const flairs = mergeFlairs(flagPublishOptions.flairs, flashTagPublishOptions.flairs);
+      const publishOptions = {
+        ...flagPublishOptions,
+        ...(flairs ? { flairs } : {}),
+      };
 
-    nonokoRedirectPathRef.current = hasNonokoOption(currentOptions) ? getBoardIndexPath() : null;
-    publishPost({ content: publishContent, ...getPublishLinkOptions(currentUrl, appliedYouTubeConversion), ...publishOptions });
-  };
+      nonokoRedirectPathRef.current = hasNonokoOption(currentOptions) ? getBoardIndexPath() : null;
+      publishPost({ content: publishContent, ...getPublishLinkOptions(currentUrl, appliedYouTubeConversion), ...publishOptions });
+    });
 
   // redirect to pending page when pending comment is created
   const navigate = useNavigate();
@@ -774,54 +784,55 @@ const PostFormTable = ({ closeForm, postCid }: { closeForm: () => void; postCid:
     setIsBbcodePreviewing(true);
   };
 
-  const onPublishReply = () => {
-    const appliedYouTubeConversion = applyPendingConversion();
+  const onPublishReply = () =>
+    runPublishSubmission(async () => {
+      const appliedYouTubeConversion = await applyPendingConversion();
 
-    const currentUrl = urlRef.current?.value.trim() || '';
-    const currentOptions = optionsRef.current?.value || '';
-    const currentOptionsError = getPostOptionsValidationError(currentOptions, postOptionsDirectoryCode);
-    const publishContent = getContentWithOptions(textRef.current?.value || '', currentOptions, fortuneEntryRef, diceRollRef, postOptionsDirectoryCode);
+      const currentUrl = urlRef.current?.value.trim() || '';
+      const currentOptions = optionsRef.current?.value || '';
+      const currentOptionsError = getPostOptionsValidationError(currentOptions, postOptionsDirectoryCode);
+      const publishContent = getContentWithOptions(textRef.current?.value || '', currentOptions, fortuneEntryRef, diceRollRef, postOptionsDirectoryCode);
 
-    checkContentLength.cancel();
-    checkPostOptions.cancel();
-    setLengthError(null);
-    setFormError(null);
-    nonokoRedirectPathRef.current = null;
+      checkContentLength.cancel();
+      checkPostOptions.cancel();
+      setLengthError(null);
+      setFormError(null);
+      nonokoRedirectPathRef.current = null;
 
-    if (currentOptionsError) {
-      setFormError(currentOptionsError);
-      return;
-    }
+      if (currentOptionsError) {
+        setFormError(currentOptionsError);
+        return;
+      }
 
-    if (!publishContent.trim() && !currentUrl) {
-      setFormError(`${t('error')}: ${t('empty_comment_alert')}`);
-      return;
-    }
+      if (!publishContent.trim() && !currentUrl) {
+        setFormError(`${t('error')}: ${t('empty_comment_alert')}`);
+        return;
+      }
 
-    if (currentUrl && !isValidPublishURL(currentUrl)) {
-      setFormError(`${t('error')}: ${t('invalid_url_alert')}`);
-      return;
-    }
-    if (currentUrl && requirePostLinkIsMedia && !isPublishFileMediaLink(currentUrl)) {
-      setFormError(`${t('error')}: ${t('link_not_image_or_video_alert')}`);
-      return;
-    }
-    const expiringMediaLinkAlert = currentUrl ? getExpiringMediaLinkAlert(currentUrl, t) : null;
-    if (expiringMediaLinkAlert) {
-      setFormError(expiringMediaLinkAlert);
-      return;
-    }
+      if (currentUrl && !isValidPublishURL(currentUrl)) {
+        setFormError(`${t('error')}: ${t('invalid_url_alert')}`);
+        return;
+      }
+      if (currentUrl && requirePostLinkIsMedia && !isPublishFileMediaLink(currentUrl)) {
+        setFormError(`${t('error')}: ${t('link_not_image_or_video_alert')}`);
+        return;
+      }
+      const expiringMediaLinkAlert = currentUrl ? getExpiringMediaLinkAlert(currentUrl, t) : null;
+      if (expiringMediaLinkAlert) {
+        setFormError(expiringMediaLinkAlert);
+        return;
+      }
 
-    if (publishContent.trim().length > 2000) {
-      setFormError(`${t('error')}: ${t('field_too_long')}`);
-      return;
-    }
+      if (publishContent.trim().length > 2000) {
+        setFormError(`${t('error')}: ${t('field_too_long')}`);
+        return;
+      }
 
-    const flagPublishOptions = getCommentFlagPublishOptionsForDirectory(directoryEntry, flagRef.current?.value);
+      const flagPublishOptions = getCommentFlagPublishOptionsForDirectory(directoryEntry, flagRef.current?.value);
 
-    nonokoRedirectPathRef.current = hasNonokoOption(currentOptions) ? getBoardIndexPath() : null;
-    publishReply({ content: publishContent, ...getPublishLinkOptions(currentUrl, appliedYouTubeConversion), ...flagPublishOptions });
-  };
+      nonokoRedirectPathRef.current = hasNonokoOption(currentOptions) ? getBoardIndexPath() : null;
+      await publishReply({ content: publishContent, ...getPublishLinkOptions(currentUrl, appliedYouTubeConversion), ...flagPublishOptions });
+    });
 
   const setLinkValue = (nextUrl: string) => {
     setUrl(nextUrl);
@@ -966,6 +977,7 @@ const PostFormTable = ({ closeForm, postCid }: { closeForm: () => void; postCid:
             handleUpload={handleUpload}
             uploadFile={uploadFile}
             onOekakiClearUploadedUrl={handleOekakiClearUploadedUrl}
+            isPublishSubmissionInFlight={isPublishSubmissionInFlight}
             disableReplyPublish={isResolvingExternalQuotes}
           />
         </tbody>
diff --git a/src/components/reply-modal/__tests__/reply-modal.test.tsx b/src/components/reply-modal/__tests__/reply-modal.test.tsx
index 3b0cf8df..48fd3a03 100644
--- a/src/components/reply-modal/__tests__/reply-modal.test.tsx
+++ b/src/components/reply-modal/__tests__/reply-modal.test.tsx
@@ -62,6 +62,7 @@ const testState = vi.hoisted(() => ({
       address: 'music-posting.eth',
     },
   } as Record<string, { address: string }>,
+  fetchMock: vi.fn(),
   showUploadControls: true,
   uploadComplete: undefined as ((url: string) => void) | undefined,
   uploadedFileName: null as string | null,
@@ -190,22 +191,32 @@ vi.mock('../../../hooks/use-stable-community', () => ({
     selector(communityAddress ? { roles: testState.rolesByCommunity[communityAddress] } : undefined),
 }));
 
-vi.mock('../../../hooks/use-publish-reply', () => ({
-  default: () => ({
-    isResolvingExternalQuotes: testState.isResolvingExternalQuotes,
-    publishReply: (options?: Record<string, unknown>) => {
-      if (options) {
-        testState.setPublishReplyOptionsMock(options);
-      }
-      return testState.publishReplyMock(options);
+vi.mock('../../../hooks/use-publish-reply', async () => {
+  const React = await vi.importActual<typeof import('react')>('react');
+
+  return {
+    default: () => {
+      const [, forceUpdate] = React.useReducer((value: number) => value + 1, 0);
+
+      return {
+        isResolvingExternalQuotes: testState.isResolvingExternalQuotes,
+        publishReply: (options?: Record<string, unknown>) => {
+          if (options) {
+            testState.setPublishReplyOptionsMock(options);
+          }
+          const result = testState.publishReplyMock(options);
+          forceUpdate();
+          return result;
+        },
+        publishReplyError: testState.publishReplyError,
+        publishReplyStateMessage: testState.publishReplyStateMessage,
+        replyIndex: testState.replyIndex,
+        resetPublishReplyOptions: testState.resetPublishReplyOptionsMock,
+        setPublishReplyOptions: (options: Record<string, unknown>) => testState.setPublishReplyOptionsMock(options),
+      };
     },
-    publishReplyError: testState.publishReplyError,
-    publishReplyStateMessage: testState.publishReplyStateMessage,
-    replyIndex: testState.replyIndex,
-    resetPublishReplyOptions: testState.resetPublishReplyOptionsMock,
-    setPublishReplyOptions: (options: Record<string, unknown>) => testState.setPublishReplyOptionsMock(options),
-  }),
-}));
+  };
+});
 
 vi.mock('../../../hooks/use-is-mobile', () => ({
   default: () => testState.isMobile,
@@ -452,6 +463,14 @@ describe('ReplyModal', () => {
         address: 'traditional-games.bso',
       },
     };
+    testState.fetchMock.mockReset();
+    testState.fetchMock.mockResolvedValue({
+      headers: {
+        get: (name: string) => (name.toLowerCase() === 'content-length' ? '12345' : null),
+      },
+      ok: true,
+    });
+    vi.stubGlobal('fetch', testState.fetchMock);
     testState.showUploadControls = true;
     testState.uploadComplete = undefined;
     testState.uploadedFileName = null;
@@ -467,6 +486,7 @@ describe('ReplyModal', () => {
     container.remove();
     document.body.style.userSelect = '';
     document.body.style.webkitUserSelect = '';
+    vi.unstubAllGlobals();
   });
 
   it('initializes quoted content, display name, upload controls, and shared offline warning on board routes', async () => {
@@ -772,7 +792,7 @@ describe('ReplyModal', () => {
 
   it('moves YouTube links into reply content and publishes the thumbnail link on media-only boards', async () => {
     const youtubeLink = 'https://youtu.be/reply123';
-    const thumbnailLink = 'https://img.youtube.com/vi/reply123/0.jpg';
+    const thumbnailLink = 'https://img.youtube.com/vi/reply123/maxresdefault.jpg';
     testState.openEmpty = true;
     testState.selectedText = 'reply body';
     testState.directoryByAddress['music-posting.eth'] = {
@@ -808,6 +828,84 @@ describe('ReplyModal', () => {
     });
   });
 
+  it('rejects unresolved YouTube links on media-only reply modal boards', async () => {
+    const youtubeLink = 'https://youtu.be/replymissing';
+    testState.fetchMock.mockResolvedValue({
+      headers: {
+        get: () => null,
+      },
+      ok: false,
+    });
+    testState.openEmpty = true;
+    testState.selectedText = 'reply body';
+    testState.directoryByAddress['music-posting.eth'] = {
+      address: 'music-posting.eth',
+      features: { requirePostLinkIsMedia: true },
+      title: '/mu/ - Music',
+    };
+
+    await renderReplyModal('/mu/thread/post-1');
+
+    const linkInput = container.querySelectorAll<HTMLInputElement>('input[type="text"]')[2];
+
+    await dispatchInput(linkInput, youtubeLink);
+    await clickButtonByText('post');
+    await flushEffects(8);
+
+    expect(testState.fetchMock).toHaveBeenCalled();
+    expect(container.textContent).toContain('error: link_not_image_or_video_alert');
+    expect(linkInput.value).toBe(youtubeLink);
+    expect(testState.publishReplyMock).not.toHaveBeenCalled();
+  });
+
+  it('ignores duplicate reply clicks while youtube thumbnail resolution is pending', async () => {
+    const youtubeLink = 'https://youtu.be/replyslow';
+    const thumbnailLink = 'https://img.youtube.com/vi/replyslow/maxresdefault.jpg';
+    let resolveFetch: (response: unknown) => void = () => {};
+    const fetchPromise = new Promise((resolve) => {
+      resolveFetch = resolve;
+    });
+    testState.fetchMock.mockReturnValue(fetchPromise);
+    testState.openEmpty = true;
+    testState.selectedText = 'reply body';
+    testState.directoryByAddress['music-posting.eth'] = {
+      address: 'music-posting.eth',
+      features: { requirePostLinkIsMedia: true },
+      title: '/mu/ - Music',
+    };
+
+    await renderReplyModal('/mu/thread/post-1');
+
+    const linkInput = container.querySelectorAll<HTMLInputElement>('input[type="text"]')[2];
+    const postButton = Array.from(container.querySelectorAll('button')).find((button) => button.textContent === 'post') as HTMLButtonElement;
+
+    await dispatchInput(linkInput, youtubeLink);
+
+    await clickButtonByText('post');
+    expect(postButton.disabled).toBe(true);
+
+    await clickButtonByText('post');
+    expect(testState.fetchMock).toHaveBeenCalledTimes(1);
+    expect(testState.publishReplyMock).not.toHaveBeenCalled();
+
+    await act(async () => {
+      resolveFetch({
+        headers: {
+          get: (name: string) => (name.toLowerCase() === 'content-length' ? '12345' : null),
+        },
+        ok: true,
+      });
+      await fetchPromise;
+      await Promise.resolve();
+    });
+
+    expect(testState.publishReplyMock).toHaveBeenCalledTimes(1);
+    expect(testState.publishReplyMock).toHaveBeenCalledWith({
+      content: `${youtubeLink}\nreply body`,
+      link: thumbnailLink,
+    });
+  });
+
   it('validates unsupported options and keeps fortune output out of preview state until reply publish', async () => {
     const randomSpy = vi.spyOn(Math, 'random').mockReturnValue(0.25);
     testState.openEmpty = true;
@@ -1065,6 +1163,7 @@ describe('ReplyModal', () => {
     await dispatchInput(optionsInput, 'nonoko');
     await dispatchInput(textarea as HTMLTextAreaElement, 'reply body');
     await clickButtonByText('post');
+    await flushEffects();
     await rerenderReplyModal('/mu/thread/post-1');
 
     expect(testState.publishReplyMock).toHaveBeenCalledTimes(1);
diff --git a/src/components/reply-modal/reply-modal.tsx b/src/components/reply-modal/reply-modal.tsx
index 9cb4aaf5..c61d146c 100644
--- a/src/components/reply-modal/reply-modal.tsx
+++ b/src/components/reply-modal/reply-modal.tsx
@@ -3,7 +3,7 @@ import { useLocation, useNavigate, useParams } from 'react-router-dom';
 import { useTranslation } from 'react-i18next';
 import type { TFunction } from 'i18next';
 import { setAccount, useAccount } from '@bitsocial/bitsocial-react-hooks';
-import { getExpiringMediaLinkAlert, getPublishFileDisplayName, getPublishLinkOptions } from '../../lib/utils/media-link-validation-utils';
+import { getExpiringMediaLinkAlert, getPublishFileDisplayName, getPublishLinkOptions, isPublishFileMediaLink } from '../../lib/utils/media-link-validation-utils';
 import { getTwimgMediaFilePublishUrl } from '../../lib/utils/media-utils';
 import { getCommentFlagOptionsForDirectory, getCommentFlagPublishOptionsForDirectory } from '../../lib/comment-flag-selection';
 import {
@@ -33,6 +33,7 @@ import usePublishReply from '../../hooks/use-publish-reply';
 import useIsMobile from '../../hooks/use-is-mobile';
 import { useFileUpload } from '../../hooks/use-file-upload';
 import { useYouTubeThumbnailLinkConversion } from '../../hooks/use-youtube-thumbnail-link-conversion';
+import usePublishSubmissionGuard from '../../hooks/use-publish-submission-guard';
 import { useCommunityField } from '../../hooks/use-stable-community';
 import { OEKAKI_WEB_WARNING_TEXT } from '../../lib/oekaki/oekaki-copy';
 import BbcodeEditorToolbar, { BbcodePreview } from '../bbcode-editor-toolbar/bbcode-editor-toolbar';
@@ -127,6 +128,7 @@ const ReplyModal = ({ closeModal, showReplyModal, parentCid, parentNumber, threa
   const [isBbcodePreviewing, setIsBbcodePreviewing] = useState(false);
   const [bbcodePreviewContent, setBbcodePreviewContent] = useState('');
   const [showTexPreview, setShowTexPreview] = useState(false);
+  const { isPublishSubmissionInFlight, runPublishSubmission } = usePublishSubmissionGuard();
   const texButtonRef = useRef<HTMLButtonElement>(null);
   // Blur in the close handler so the TeX button doesn't keep a lingering focus state
   // (focus-visible promotion on Escape, focus-triggered tooltip) after the preview closes.
@@ -157,51 +159,56 @@ const ReplyModal = ({ closeModal, showReplyModal, parentCid, parentNumber, threa
     }, POST_OPTIONS_VALIDATION_DELAY_MS),
   );
 
-  const onPublishReply = () => {
-    const appliedYouTubeConversion = applyPendingConversion();
+  const onPublishReply = () =>
+    runPublishSubmission(async () => {
+      const appliedYouTubeConversion = await applyPendingConversion();
 
-    const currentContent = textRef.current?.value || '';
-    const currentUrl = urlRef.current?.value.trim() || '';
-    const currentOptions = optionsRef.current?.value || '';
-    const currentOptionsError = getPostOptionsValidationError(currentOptions, postOptionsDirectoryCode);
-    const publishContent = getContentWithOptions(currentContent, currentOptions, fortuneEntryRef, diceRollRef, postOptionsDirectoryCode);
+      const currentContent = textRef.current?.value || '';
+      const currentUrl = urlRef.current?.value.trim() || '';
+      const currentOptions = optionsRef.current?.value || '';
+      const currentOptionsError = getPostOptionsValidationError(currentOptions, postOptionsDirectoryCode);
+      const publishContent = getContentWithOptions(currentContent, currentOptions, fortuneEntryRef, diceRollRef, postOptionsDirectoryCode);
 
-    checkContentLengthRef.current.cancel();
-    checkPostOptionsRef.current.cancel();
-    setLengthError(null);
-    nonokoRedirectPathRef.current = null;
+      checkContentLengthRef.current.cancel();
+      checkPostOptionsRef.current.cancel();
+      setLengthError(null);
+      nonokoRedirectPathRef.current = null;
 
-    if (currentOptionsError) {
-      setError(currentOptionsError);
-      return;
-    }
+      if (currentOptionsError) {
+        setError(currentOptionsError);
+        return;
+      }
 
-    if (!publishContent.trim() && !currentUrl) {
-      setError(t('error') + ': ' + t('empty_comment_alert'));
-      return;
-    }
+      if (!publishContent.trim() && !currentUrl) {
+        setError(t('error') + ': ' + t('empty_comment_alert'));
+        return;
+      }
 
-    if (currentUrl && !isValidPublishURL(currentUrl)) {
-      setError(t('error') + ': ' + t('invalid_url_alert'));
-      return;
-    }
-    const expiringMediaLinkAlert = currentUrl ? getExpiringMediaLinkAlert(currentUrl, t) : null;
-    if (expiringMediaLinkAlert) {
-      setError(expiringMediaLinkAlert);
-      return;
-    }
+      if (currentUrl && !isValidPublishURL(currentUrl)) {
+        setError(t('error') + ': ' + t('invalid_url_alert'));
+        return;
+      }
+      if (currentUrl && requirePostLinkIsMedia && !isPublishFileMediaLink(currentUrl)) {
+        setError(t('error') + ': ' + t('link_not_image_or_video_alert'));
+        return;
+      }
+      const expiringMediaLinkAlert = currentUrl ? getExpiringMediaLinkAlert(currentUrl, t) : null;
+      if (expiringMediaLinkAlert) {
+        setError(expiringMediaLinkAlert);
+        return;
+      }
 
-    if (publishContent.trim().length > 2000) {
-      setError(t('error') + ': ' + t('field_too_long'));
-      return;
-    }
+      if (publishContent.trim().length > 2000) {
+        setError(t('error') + ': ' + t('field_too_long'));
+        return;
+      }
 
-    const flagPublishOptions = getCommentFlagPublishOptionsForDirectory(directoryEntry, flagRef.current?.value);
+      const flagPublishOptions = getCommentFlagPublishOptionsForDirectory(directoryEntry, flagRef.current?.value);
 
-    setError(null);
-    nonokoRedirectPathRef.current = hasNonokoOption(currentOptions) ? `/${postOptionsDirectoryCode || params.boardIdentifier || communityAddress}` : null;
-    publishReply({ content: publishContent, ...getPublishLinkOptions(currentUrl, appliedYouTubeConversion), ...flagPublishOptions });
-  };
+      setError(null);
+      nonokoRedirectPathRef.current = hasNonokoOption(currentOptions) ? `/${postOptionsDirectoryCode || params.boardIdentifier || communityAddress}` : null;
+      await publishReply({ content: publishContent, ...getPublishLinkOptions(currentUrl, appliedYouTubeConversion), ...flagPublishOptions });
+    });
 
   useEffect(() => {
     if (typeof replyIndex === 'number') {
@@ -698,7 +705,7 @@ const ReplyModal = ({ closeModal, showReplyModal, parentCid, parentNumber, threa
               ]
             </span>
           )}
-          <button className={styles.publishButton} disabled={isResolvingExternalQuotes} type='button' onClick={onPublishReply}>
+          <button className={styles.publishButton} disabled={isResolvingExternalQuotes || isPublishSubmissionInFlight} type='button' onClick={onPublishReply}>
             {t('post')}
           </button>
         </div>
diff --git a/src/hooks/__tests__/use-youtube-thumbnail-fallback.test.tsx b/src/hooks/__tests__/use-youtube-thumbnail-fallback.test.tsx
new file mode 100644
index 00000000..e06367eb
--- /dev/null
+++ b/src/hooks/__tests__/use-youtube-thumbnail-fallback.test.tsx
@@ -0,0 +1,64 @@
+import * as React from 'react';
+import { createElement } from 'react';
+import { createRoot, type Root } from 'react-dom/client';
+import { afterEach, beforeEach, describe, expect, it } from 'vitest';
+import { useYouTubeThumbnailFallback } from '../use-youtube-thumbnail-fallback';
+
+(globalThis as { IS_REACT_ACT_ENVIRONMENT?: boolean }).IS_REACT_ACT_ENVIRONMENT = true;
+const act = (React as { act?: (cb: () => void | Promise<void>) => void | Promise<void> }).act as (cb: () => void | Promise<void>) => void | Promise<void>;
+
+let container: HTMLDivElement;
+let root: Root;
+let latestValue: ReturnType<typeof useYouTubeThumbnailFallback>;
+
+const HookHarness = ({ thumbnailUrl }: { thumbnailUrl: string | undefined }) => {
+  latestValue = useYouTubeThumbnailFallback(thumbnailUrl);
+  return null;
+};
+
+const renderFallback = async (thumbnailUrl: string | undefined) => {
+  await act(async () => {
+    root.render(createElement(HookHarness, { thumbnailUrl }));
+  });
+};
+
+const getPlaceholderImage = () => ({ naturalHeight: 90, naturalWidth: 120 }) as HTMLImageElement;
+
+describe('useYouTubeThumbnailFallback', () => {
+  beforeEach(() => {
+    container = document.createElement('div');
+    document.body.appendChild(container);
+    root = createRoot(container);
+  });
+
+  afterEach(() => {
+    act(() => root.unmount());
+    container.remove();
+  });
+
+  it('advances to the next YouTube fallback when a placeholder loads before the final candidate', async () => {
+    await renderFallback('https://img.youtube.com/vi/missing-max/maxresdefault.jpg');
+
+    let handled = false;
+    await act(async () => {
+      handled = latestValue.handleThumbnailLoad(getPlaceholderImage());
+    });
+
+    expect(handled).toBe(true);
+    expect(latestValue.isUnavailable).toBe(false);
+    expect(latestValue.thumbnailUrl).toBe('https://img.youtube.com/vi/missing-max/sddefault.jpg');
+  });
+
+  it('marks the thumbnail unavailable when the last YouTube candidate is a placeholder', async () => {
+    await renderFallback('https://img.youtube.com/vi/missing-hq/hqdefault.jpg');
+
+    let handled = false;
+    await act(async () => {
+      handled = latestValue.handleThumbnailLoad(getPlaceholderImage());
+    });
+
+    expect(handled).toBe(true);
+    expect(latestValue.isUnavailable).toBe(true);
+    expect(latestValue.thumbnailUrl).toBeUndefined();
+  });
+});
diff --git a/src/hooks/use-publish-submission-guard.ts b/src/hooks/use-publish-submission-guard.ts
new file mode 100644
index 00000000..d9b455ed
--- /dev/null
+++ b/src/hooks/use-publish-submission-guard.ts
@@ -0,0 +1,26 @@
+import { useCallback, useRef, useState } from 'react';
+
+const usePublishSubmissionGuard = () => {
+  const publishSubmissionInFlightRef = useRef(false);
+  const [isPublishSubmissionInFlight, setIsPublishSubmissionInFlight] = useState(false);
+
+  const runPublishSubmission = useCallback(async (publish: () => Promise<void>) => {
+    if (publishSubmissionInFlightRef.current) {
+      return;
+    }
+
+    publishSubmissionInFlightRef.current = true;
+    setIsPublishSubmissionInFlight(true);
+
+    try {
+      await publish();
+    } finally {
+      publishSubmissionInFlightRef.current = false;
+      setIsPublishSubmissionInFlight(false);
+    }
+  }, []);
+
+  return { isPublishSubmissionInFlight, runPublishSubmission };
+};
+
+export default usePublishSubmissionGuard;
diff --git a/src/hooks/use-youtube-thumbnail-fallback.ts b/src/hooks/use-youtube-thumbnail-fallback.ts
new file mode 100644
index 00000000..46c23946
--- /dev/null
+++ b/src/hooks/use-youtube-thumbnail-fallback.ts
@@ -0,0 +1,48 @@
+import { useCallback, useMemo, useState } from 'react';
+import { getYouTubeThumbnailFallbackUrls, isMissingYouTubeThumbnailImage } from '../lib/utils/media-utils';
+
+interface YouTubeThumbnailFallbackState {
+  sourceUrl?: string;
+  index: number;
+  unavailable: boolean;
+}
+
+export const useYouTubeThumbnailFallback = (thumbnailUrl: string | undefined) => {
+  const fallbackUrls = useMemo(() => getYouTubeThumbnailFallbackUrls(thumbnailUrl), [thumbnailUrl]);
+  const [state, setState] = useState<YouTubeThumbnailFallbackState>({ index: 0, unavailable: false });
+  const index = state.sourceUrl === thumbnailUrl ? state.index : 0;
+  const unavailable = state.sourceUrl === thumbnailUrl ? state.unavailable : false;
+  const resolvedThumbnailUrl = unavailable ? undefined : (fallbackUrls[index] ?? thumbnailUrl);
+
+  const advance = useCallback(() => {
+    if (!thumbnailUrl || !fallbackUrls.length) {
+      return false;
+    }
+
+    if (index < fallbackUrls.length - 1) {
+      setState({ index: index + 1, sourceUrl: thumbnailUrl, unavailable: false });
+      return true;
+    }
+
+    setState({ index, sourceUrl: thumbnailUrl, unavailable: true });
+    return true;
+  }, [fallbackUrls, index, thumbnailUrl]);
+
+  const handleThumbnailLoad = useCallback(
+    (image: HTMLImageElement) => {
+      if (!resolvedThumbnailUrl || !isMissingYouTubeThumbnailImage(resolvedThumbnailUrl, image.naturalWidth, image.naturalHeight)) {
+        return false;
+      }
+
+      return advance();
+    },
+    [advance, resolvedThumbnailUrl],
+  );
+
+  return {
+    handleThumbnailError: advance,
+    handleThumbnailLoad,
+    isUnavailable: unavailable,
+    thumbnailUrl: resolvedThumbnailUrl,
+  };
+};
diff --git a/src/hooks/use-youtube-thumbnail-link-conversion.ts b/src/hooks/use-youtube-thumbnail-link-conversion.ts
index d94da17b..6e46690d 100644
--- a/src/hooks/use-youtube-thumbnail-link-conversion.ts
+++ b/src/hooks/use-youtube-thumbnail-link-conversion.ts
@@ -1,5 +1,5 @@
 import { useCallback, useEffect, useRef, useState } from 'react';
-import { getYouTubeThumbnailUrlFromLink } from '../lib/utils/media-utils';
+import { getBestAvailableYouTubeThumbnailUrlFromLink, getYouTubeThumbnailUrlFromLink } from '../lib/utils/media-utils';
 
 const YOUTUBE_THUMBNAIL_LINK_CONVERSION_DELAY_SECONDS = 3;
 const YOUTUBE_THUMBNAIL_LINK_CONVERSION_INTERVAL_MS = 1000;
@@ -9,7 +9,7 @@ type ElementRef<T extends HTMLElement> = {
 };
 
 interface PendingYouTubeThumbnailLinkConversion {
-  thumbnailLink: string;
+  thumbnailLinkPromise: Promise<string | undefined>;
   youtubeLink: string;
 }
 
@@ -29,13 +29,13 @@ const getContentWithYouTubeLinkAtTop = (content: string, youtubeLink: string): s
 
 const getPendingConversion = (link: string): PendingYouTubeThumbnailLinkConversion | null => {
   const youtubeLink = link.trim();
-  const thumbnailLink = getYouTubeThumbnailUrlFromLink(youtubeLink);
+  const preferredThumbnailLink = getYouTubeThumbnailUrlFromLink(youtubeLink);
 
-  if (!youtubeLink || !thumbnailLink || youtubeLink === thumbnailLink) {
+  if (!youtubeLink || !preferredThumbnailLink || youtubeLink === preferredThumbnailLink) {
     return null;
   }
 
-  return { thumbnailLink, youtubeLink };
+  return { thumbnailLinkPromise: getBestAvailableYouTubeThumbnailUrlFromLink(youtubeLink), youtubeLink };
 };
 
 export const useYouTubeThumbnailLinkConversion = ({ enabled, onContentChange, onLinkChange, textRef, urlRef }: UseYouTubeThumbnailLinkConversionOptions) => {
@@ -56,7 +56,7 @@ export const useYouTubeThumbnailLinkConversion = ({ enabled, onContentChange, on
     setNoticeCountdown(null);
   }, [clearCountdownTimer]);
 
-  const applyPendingConversion = useCallback(() => {
+  const applyPendingConversion = useCallback(async () => {
     if (!enabled) {
       cancelPendingConversion();
       return false;
@@ -69,6 +69,13 @@ export const useYouTubeThumbnailLinkConversion = ({ enabled, onContentChange, on
       return false;
     }
 
+    const thumbnailLink = await pendingConversion.thumbnailLinkPromise;
+    const latestLink = urlRef.current?.value.trim() || '';
+    if (!thumbnailLink || latestLink !== pendingConversion.youtubeLink) {
+      cancelPendingConversion();
+      return false;
+    }
+
     clearCountdownTimer();
     pendingConversionRef.current = null;
     setNoticeCountdown(null);
@@ -80,11 +87,11 @@ export const useYouTubeThumbnailLinkConversion = ({ enabled, onContentChange, on
       textRef.current.value = nextContent;
     }
     if (urlRef.current) {
-      urlRef.current.value = pendingConversion.thumbnailLink;
+      urlRef.current.value = thumbnailLink;
     }
 
     onContentChange(nextContent);
-    onLinkChange(pendingConversion.thumbnailLink);
+    onLinkChange(thumbnailLink);
     return true;
   }, [cancelPendingConversion, clearCountdownTimer, enabled, onContentChange, onLinkChange, textRef, urlRef]);
 
@@ -99,7 +106,7 @@ export const useYouTubeThumbnailLinkConversion = ({ enabled, onContentChange, on
         }
 
         if (seconds <= 0) {
-          applyPendingConversion();
+          void applyPendingConversion();
           return;
         }
 
diff --git a/src/lib/utils/__tests__/media-utils.test.ts b/src/lib/utils/__tests__/media-utils.test.ts
index c2ee72bb..f9c2ac65 100644
--- a/src/lib/utils/__tests__/media-utils.test.ts
+++ b/src/lib/utils/__tests__/media-utils.test.ts
@@ -4,6 +4,7 @@ const testState = vi.hoisted(() => ({
   cachedThumbnails: new Map<string, string>(),
   canEmbedHosts: new Set<string>(),
   capacitorHttpGetMock: vi.fn(),
+  capacitorHttpRequestMock: vi.fn(),
   consoleErrorMock: vi.fn(),
   fetchMock: vi.fn(),
   isNativePlatform: false,
@@ -34,10 +35,12 @@ vi.mock('@capacitor/core', () => ({
   },
   CapacitorHttp: {
     get: (options: unknown) => testState.capacitorHttpGetMock(options),
+    request: (options: unknown) => testState.capacitorHttpRequestMock(options),
   },
 }));
 
 import {
+  getBestAvailableYouTubeThumbnailUrlFromLink,
   fetchWebpageThumbnailIfNeeded,
   getCommentMediaInfo,
   getDisplayMediaInfoType,
@@ -47,7 +50,10 @@ import {
   getPostMediaTypeLabel,
   getTwimgMediaFilePublishUrl,
   getYouTubeEmbedPostMediaFileLink,
+  getYouTubeThumbnailCandidateUrlsFromLink,
+  getYouTubeThumbnailFallbackUrls,
   getYouTubeThumbnailUrlFromLink,
+  isMissingYouTubeThumbnailImage,
 } from '../media-utils';
 
 const clearMemoizedCache = (fn: unknown) => {
@@ -78,6 +84,20 @@ const createFetchResponse = (html: string, ok = true) => {
   };
 };
 
+const createHeadResponse = (ok: boolean, contentLength = '12345') => ({
+  headers: {
+    get: (name: string) => (name.toLowerCase() === 'content-length' ? contentLength : null),
+  },
+  ok,
+});
+
+const createNativeHeadResponse = (status: number, contentLength = '12345') => ({
+  headers: {
+    'Content-Length': contentLength,
+  },
+  status,
+});
+
 describe('media-utils', () => {
   let consoleErrorSpy: ReturnType<typeof vi.spyOn>;
 
@@ -92,6 +112,7 @@ describe('media-utils', () => {
     });
     testState.fetchMock.mockReset();
     testState.capacitorHttpGetMock.mockReset();
+    testState.capacitorHttpRequestMock.mockReset();
     vi.stubGlobal('fetch', testState.fetchMock);
     clearMemoizedCache(getHasThumbnail);
     clearMemoizedCache(getLinkMediaInfo);
@@ -119,18 +140,87 @@ describe('media-utils', () => {
 
   it('uses the youtube thumbnail url for post media file links and labels', () => {
     const mediaInfo = {
-      patternThumbnailUrl: 'https://img.youtube.com/vi/abc123/0.jpg',
+      patternThumbnailUrl: 'https://img.youtube.com/vi/abc123/maxresdefault.jpg',
       type: 'iframe',
       url: 'https://www.youtube.com/watch?v=abc123',
     };
 
-    expect(getYouTubeEmbedPostMediaFileLink(mediaInfo)).toBe('https://img.youtube.com/vi/abc123/0.jpg');
+    expect(getYouTubeEmbedPostMediaFileLink(mediaInfo)).toBe('https://img.youtube.com/vi/abc123/maxresdefault.jpg');
     expect(getPostMediaTypeLabel(mediaInfo, 'iframe', (key) => key)).toBe('youtube_video');
     expect(getYouTubeEmbedPostMediaFileLink({ type: 'iframe', url: 'https://streamable.com/clip123' })).toBeUndefined();
-    expect(getYouTubeThumbnailUrlFromLink('https://youtu.be/short123')).toBe('https://img.youtube.com/vi/short123/0.jpg');
+    expect(getYouTubeThumbnailUrlFromLink('https://youtu.be/short123')).toBe('https://img.youtube.com/vi/short123/maxresdefault.jpg');
     expect(getYouTubeThumbnailUrlFromLink('https://example.com/watch?v=not-youtube')).toBeUndefined();
   });
 
+  it('builds youtube thumbnail candidates and detects the served missing-thumbnail placeholder', () => {
+    expect(getYouTubeThumbnailCandidateUrlsFromLink('https://www.youtube.com/watch?v=abc123')).toEqual([
+      'https://img.youtube.com/vi/abc123/maxresdefault.jpg',
+      'https://img.youtube.com/vi/abc123/sddefault.jpg',
+      'https://img.youtube.com/vi/abc123/mqdefault.jpg',
+      'https://img.youtube.com/vi/abc123/hqdefault.jpg',
+    ]);
+    expect(getYouTubeThumbnailFallbackUrls('https://i3.ytimg.com/vi/abc123/maxresdefault.jpg')).toEqual([
+      'https://i3.ytimg.com/vi/abc123/maxresdefault.jpg',
+      'https://img.youtube.com/vi/abc123/sddefault.jpg',
+      'https://img.youtube.com/vi/abc123/mqdefault.jpg',
+      'https://img.youtube.com/vi/abc123/hqdefault.jpg',
+    ]);
+    expect(getYouTubeThumbnailFallbackUrls('https://i3.ytimg.com/vi/abc123/sddefault.jpg')).toEqual([
+      'https://i3.ytimg.com/vi/abc123/sddefault.jpg',
+      'https://img.youtube.com/vi/abc123/mqdefault.jpg',
+      'https://img.youtube.com/vi/abc123/hqdefault.jpg',
+    ]);
+    expect(isMissingYouTubeThumbnailImage('https://i3.ytimg.com/vi/abc123/maxresdefault.jpg', 120, 90)).toBe(true);
+    expect(isMissingYouTubeThumbnailImage('https://i3.ytimg.com/vi/abc123/maxresdefault.jpg', 1280, 720)).toBe(false);
+    expect(isMissingYouTubeThumbnailImage('https://example.com/thumb.jpg', 120, 90)).toBe(false);
+  });
+
+  it('resolves the best available youtube thumbnail without accepting the failed placeholder response', async () => {
+    testState.fetchMock
+      .mockResolvedValueOnce(createHeadResponse(false, '1097'))
+      .mockResolvedValueOnce(createHeadResponse(true, '1097'))
+      .mockResolvedValueOnce(createHeadResponse(true, '8710'));
+
+    await expect(getBestAvailableYouTubeThumbnailUrlFromLink('https://www.youtube.com/watch?v=resolve123')).resolves.toBe(
+      'https://img.youtube.com/vi/resolve123/mqdefault.jpg',
+    );
+    expect(testState.fetchMock).toHaveBeenNthCalledWith(1, 'https://img.youtube.com/vi/resolve123/maxresdefault.jpg', expect.objectContaining({ method: 'HEAD' }));
+    expect(testState.fetchMock).toHaveBeenNthCalledWith(2, 'https://img.youtube.com/vi/resolve123/sddefault.jpg', expect.objectContaining({ method: 'HEAD' }));
+    expect(testState.fetchMock).toHaveBeenNthCalledWith(3, 'https://img.youtube.com/vi/resolve123/mqdefault.jpg', expect.objectContaining({ method: 'HEAD' }));
+  });
+
+  it('uses native http requests when resolving youtube thumbnails in native builds', async () => {
+    testState.isNativePlatform = true;
+    testState.capacitorHttpRequestMock.mockResolvedValueOnce(createNativeHeadResponse(404, '1097')).mockResolvedValueOnce(createNativeHeadResponse(200, '8765'));
+
+    await expect(getBestAvailableYouTubeThumbnailUrlFromLink('https://www.youtube.com/watch?v=native123')).resolves.toBe(
+      'https://img.youtube.com/vi/native123/sddefault.jpg',
+    );
+    expect(testState.fetchMock).not.toHaveBeenCalled();
+    expect(testState.capacitorHttpRequestMock).toHaveBeenNthCalledWith(
+      1,
+      expect.objectContaining({
+        connectTimeout: 3000,
+        method: 'HEAD',
+        readTimeout: 3000,
+        url: 'https://img.youtube.com/vi/native123/maxresdefault.jpg',
+      }),
+    );
+    expect(testState.capacitorHttpRequestMock).toHaveBeenNthCalledWith(
+      2,
+      expect.objectContaining({
+        method: 'HEAD',
+        url: 'https://img.youtube.com/vi/native123/sddefault.jpg',
+      }),
+    );
+  });
+
+  it('returns no youtube thumbnail when every candidate is unavailable', async () => {
+    testState.fetchMock.mockResolvedValue(createHeadResponse(false, '1097'));
+
+    await expect(getBestAvailableYouTubeThumbnailUrlFromLink('https://www.youtube.com/watch?v=missing123')).resolves.toBeUndefined();
+  });
+
   it('recognizes which media types expose thumbnails', () => {
     expect(getHasThumbnail(undefined, 'https://example.com/file.png')).toBe(false);
     expect(getHasThumbnail({ type: 'image', url: 'https://example.com/file.png' }, 'https://example.com/file.png')).toBe(true);
@@ -141,7 +231,7 @@ describe('media-utils', () => {
     expect(getHasThumbnail({ thumbnail: 'https://example.com/thumb.png', type: 'webpage', url: 'https://example.com' }, 'https://example.com')).toBe(true);
     expect(
       getHasThumbnail(
-        { patternThumbnailUrl: 'https://img.youtube.com/vi/abc/0.jpg', type: 'iframe', url: 'https://www.youtube.com/watch?v=abc' },
+        { patternThumbnailUrl: 'https://img.youtube.com/vi/abc/maxresdefault.jpg', type: 'iframe', url: 'https://www.youtube.com/watch?v=abc' },
         'https://www.youtube.com/watch?v=abc',
       ),
     ).toBe(true);
@@ -171,7 +261,7 @@ describe('media-utils', () => {
     expect(getLinkMediaInfo('https://example.com/file.swf')).toMatchObject({ type: 'swf' });
     expect(getLinkMediaInfo('https://example.com/path')).toMatchObject({ type: 'webpage' });
     expect(getLinkMediaInfo('https://www.youtube.com/watch?v=abc123')).toEqual({
-      patternThumbnailUrl: 'https://img.youtube.com/vi/abc123/0.jpg',
+      patternThumbnailUrl: 'https://img.youtube.com/vi/abc123/maxresdefault.jpg',
       type: 'iframe',
       url: 'https://www.youtube.com/watch?v=abc123',
     });
@@ -181,13 +271,13 @@ describe('media-utils', () => {
       url: 'https://streamable.com/clip123',
     });
     expect(getLinkMediaInfo('https://yt.example/watch?v=yt123')).toEqual({
-      patternThumbnailUrl: 'https://img.youtube.com/vi/yt123/0.jpg',
+      patternThumbnailUrl: 'https://img.youtube.com/vi/yt123/maxresdefault.jpg',
       type: 'iframe',
       url: 'https://yt.example/watch?v=yt123',
     });
     testState.canEmbedHosts = new Set(['yewtu.be']);
     expect(getLinkMediaInfo('https://yewtu.be/invidious123')).toEqual({
-      patternThumbnailUrl: 'https://img.youtube.com/vi/invidious123/0.jpg',
+      patternThumbnailUrl: 'https://img.youtube.com/vi/invidious123/maxresdefault.jpg',
       type: 'iframe',
       url: 'https://yewtu.be/invidious123',
     });
@@ -237,7 +327,7 @@ describe('media-utils', () => {
     expect(getCommentMediaInfo('https://www.youtube.com/watch?v=abc123', '', 800, 450)).toEqual({
       linkHeight: 450,
       linkWidth: 800,
-      patternThumbnailUrl: 'https://img.youtube.com/vi/abc123/0.jpg',
+      patternThumbnailUrl: 'https://img.youtube.com/vi/abc123/maxresdefault.jpg',
       thumbnail: undefined,
       type: 'iframe',
       url: 'https://www.youtube.com/watch?v=abc123',
diff --git a/src/lib/utils/media-utils.ts b/src/lib/utils/media-utils.ts
index cd96b27c..53caa6ca 100644
--- a/src/lib/utils/media-utils.ts
+++ b/src/lib/utils/media-utils.ts
@@ -66,19 +66,146 @@ export const getPostMediaTypeLabel = (commentMediaInfo: CommentMediaInfo | undef
 };
 
 const isYouTubeLikeUrl = (url: URL): boolean => youtubeHosts.has(url.host) || url.host.startsWith('yt.');
+const YOUTUBE_THUMBNAIL_FILENAMES = ['maxresdefault.jpg', 'sddefault.jpg', 'mqdefault.jpg', 'hqdefault.jpg'] as const;
+const YOUTUBE_MISSING_THUMBNAIL_CONTENT_LENGTH = '1097';
+const YOUTUBE_MISSING_THUMBNAIL_HEIGHT = 90;
+const YOUTUBE_MISSING_THUMBNAIL_WIDTH = 120;
+const YOUTUBE_THUMBNAIL_RESOLUTION_TIMEOUT_MS = 3000;
+const youtubeThumbnailResolutionPromises = new Map<string, Promise<string | undefined>>();
 
-export const getYouTubeThumbnailUrl = (url: URL): string | undefined => {
-  if (!isYouTubeLikeUrl(url)) {
+const getHeaderValue = (headers: Record<string, string>, headerName: string): string | undefined => {
+  const matchingHeader = Object.entries(headers).find(([name]) => name.toLowerCase() === headerName);
+  return matchingHeader?.[1];
+};
+
+const getYouTubeThumbnailUrlFromVideoId = (videoId: string, filename: (typeof YOUTUBE_THUMBNAIL_FILENAMES)[number]): string => {
+  return `https://img.youtube.com/vi/${videoId}/${filename}`;
+};
+
+const getYouTubeThumbnailVideoId = (url: URL): string | undefined => {
+  const hostname = url.hostname.toLowerCase();
+  if (hostname !== 'img.youtube.com' && hostname !== 'i.ytimg.com' && !/^i\d+\.ytimg\.com$/.test(hostname)) {
     return undefined;
   }
 
+  const pathParts = url.pathname.split('/').filter(Boolean);
+  if (pathParts.length !== 3 || pathParts[0] !== 'vi') {
+    return undefined;
+  }
+
+  return pathParts[1];
+};
+
+export const getYouTubeThumbnailCandidateUrls = (url: URL): string[] => {
+  if (!isYouTubeLikeUrl(url)) {
+    return [];
+  }
+
   const videoId = getYouTubeVideoId(url);
-  return videoId ? `https://img.youtube.com/vi/${videoId}/0.jpg` : undefined;
+  return videoId ? YOUTUBE_THUMBNAIL_FILENAMES.map((filename) => getYouTubeThumbnailUrlFromVideoId(videoId, filename)) : [];
+};
+
+export const getYouTubeThumbnailCandidateUrlsFromLink = (link: string): string[] => {
+  const parsedUrl = parseHttpUrl(link.trim());
+  return parsedUrl ? getYouTubeThumbnailCandidateUrls(parsedUrl) : [];
+};
+
+export const getYouTubeThumbnailFallbackUrls = (thumbnailUrl: string | undefined): string[] => {
+  if (!thumbnailUrl) {
+    return [];
+  }
+
+  const parsedUrl = parseHttpUrl(thumbnailUrl);
+  const videoId = parsedUrl ? getYouTubeThumbnailVideoId(parsedUrl) : undefined;
+  if (!videoId) {
+    return [thumbnailUrl];
+  }
+
+  const currentFilename = parsedUrl?.pathname.split('/').filter(Boolean)[2];
+  const startIndex = YOUTUBE_THUMBNAIL_FILENAMES.findIndex((filename) => filename === currentFilename);
+  const filenames = startIndex >= 0 ? YOUTUBE_THUMBNAIL_FILENAMES.slice(startIndex) : YOUTUBE_THUMBNAIL_FILENAMES;
+
+  return filenames.map((filename) => (filename === currentFilename ? thumbnailUrl : getYouTubeThumbnailUrlFromVideoId(videoId, filename)));
+};
+
+export const isMissingYouTubeThumbnailImage = (thumbnailUrl: string, width: number, height: number): boolean => {
+  const parsedUrl = parseHttpUrl(thumbnailUrl);
+  return Boolean(parsedUrl && getYouTubeThumbnailVideoId(parsedUrl) && width === YOUTUBE_MISSING_THUMBNAIL_WIDTH && height === YOUTUBE_MISSING_THUMBNAIL_HEIGHT);
+};
+
+export const getYouTubeThumbnailUrl = (url: URL): string | undefined => {
+  return getYouTubeThumbnailCandidateUrls(url)[0];
 };
 
 export const getYouTubeThumbnailUrlFromLink = (link: string): string | undefined => {
-  const parsedUrl = parseHttpUrl(link.trim());
-  return parsedUrl ? getYouTubeThumbnailUrl(parsedUrl) : undefined;
+  return getYouTubeThumbnailCandidateUrlsFromLink(link)[0];
+};
+
+const isAvailableYouTubeThumbnailUrl = async (thumbnailUrl: string): Promise<boolean> => {
+  if (Capacitor.isNativePlatform()) {
+    try {
+      const response = await CapacitorHttp.request({
+        url: thumbnailUrl,
+        method: 'HEAD',
+        readTimeout: YOUTUBE_THUMBNAIL_RESOLUTION_TIMEOUT_MS,
+        connectTimeout: YOUTUBE_THUMBNAIL_RESOLUTION_TIMEOUT_MS,
+      });
+
+      return response.status >= 200 && response.status < 300 && getHeaderValue(response.headers, 'content-length') !== YOUTUBE_MISSING_THUMBNAIL_CONTENT_LENGTH;
+    } catch {
+      return false;
+    }
+  }
+
+  if (typeof fetch !== 'function') {
+    return false;
+  }
+
+  const controller = new AbortController();
+  const timeoutId = globalThis.setTimeout(() => controller.abort(), YOUTUBE_THUMBNAIL_RESOLUTION_TIMEOUT_MS);
+
+  try {
+    const response = await fetch(thumbnailUrl, {
+      method: 'HEAD',
+      signal: controller.signal,
+    });
+
+    return response.ok && response.headers.get('content-length') !== YOUTUBE_MISSING_THUMBNAIL_CONTENT_LENGTH;
+  } catch {
+    return false;
+  } finally {
+    globalThis.clearTimeout(timeoutId);
+  }
+};
+
+export const getBestAvailableYouTubeThumbnailUrlFromLink = (link: string): Promise<string | undefined> => {
+  const candidateUrls = getYouTubeThumbnailCandidateUrlsFromLink(link);
+  if (!candidateUrls.length) {
+    return Promise.resolve(undefined);
+  }
+
+  const cacheKey = candidateUrls.join('\n');
+  const cachedPromise = youtubeThumbnailResolutionPromises.get(cacheKey);
+  if (cachedPromise) {
+    return cachedPromise;
+  }
+
+  const resolutionPromise = (async () => {
+    for (const candidateUrl of candidateUrls) {
+      if (await isAvailableYouTubeThumbnailUrl(candidateUrl)) {
+        return candidateUrl;
+      }
+    }
+    return undefined;
+  })().then((thumbnailUrl) => {
+    if (!thumbnailUrl) {
+      youtubeThumbnailResolutionPromises.delete(cacheKey);
+    }
+    return thumbnailUrl;
+  });
+
+  youtubeThumbnailResolutionPromises.set(cacheKey, resolutionPromise);
+  return resolutionPromise;
 };
 
 export const getHasThumbnail = memoize(