feat: gallery — video lightbox, auto-scroll load, month separators; fix 3 review bugs

New features:
- Video playback: lightbox renders <video controls autoPlay> for MsgType.Video;
  thumbnail tiles show a play-button badge overlay; LightboxImage renamed to
  LightboxMedia to handle both types.
- Auto-load on scroll: IntersectionObserver on a sentinel div replaces the
  manual "Load More" button. Detaches while loading or when history is exhausted.
- Month separators: image/video grid grouped by month ("June 2026", etc.) with
  a hairline divider; separator only shown when more than one month is present.

Bugs fixed by code review:
- flatIdx++: index was incremented before the !thumbMxc null-guard, causing
  tiles rendered after a skipped event to open the wrong lightbox item. Guard
  is now checked first; flatIdx only increments when a tile actually renders.
- lightboxIndex never reset on tab switch: stale index kept the lightbox open
  (or opened the wrong item) after switching tabs. handleTabChange() now calls
  setLightboxIndex(null) alongside setTab().
- Silent catch retry storm: pagination errors left canLoadMore=true, causing
  the IntersectionObserver to re-fire handleLoadMore on every render cycle
  when the sentinel was still visible. Error state now sets loadError=true,
  removes the sentinel, and shows a manual Retry button instead.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/features/room/MediaGallery.tsx

@@ -16,7 +16,6 @@ import {
 } from 'folds';
 import { EventType, MatrixClient, MatrixEvent, MsgType, Room } from 'matrix-js-sdk';
 import { IEncryptedFile, IImageInfo, IThumbnailContent } from '../../../types/matrix/common';
-import { FALLBACK_MIMETYPE } from '../../utils/mimeTypes';
 import { useMatrixClient } from '../../hooks/useMatrixClient';
 import { useMediaAuthentication } from '../../hooks/useMediaAuthentication';
 import { decryptFile, downloadEncryptedMedia, mxcUrlToHttp } from '../../utils/matrix';
@@ -36,7 +35,7 @@ const TAB_MSGTYPES: Record<GalleryTab, MsgType> = {
   file: MsgType.File,
 };
 
-// ── decrypt hook ──────────────────────────────────────────────────────────────
+// ── Decrypt hook ──────────────────────────────────────────────────────────────
 
 type DecryptState = { status: 'loading' } | { status: 'ok'; url: string } | { status: 'error' };
 
@@ -55,18 +54,15 @@ function useDecryptedMediaUrl(
       setState({ status: 'error' });
       return;
     }
-
     let cancelled = false;
-
     setState({ status: 'loading' });
 
     const run = async () => {
       const httpUrl = mxcUrlToHttp(mx, mxcUrl, useAuthentication);
       if (!httpUrl) throw new Error('bad url');
-
       if (encInfo) {
         const blob = await downloadEncryptedMedia(httpUrl, (buf) =>
-          decryptFile(buf, mimeType ?? FALLBACK_MIMETYPE, encInfo),
+          decryptFile(buf, mimeType ?? 'application/octet-stream', encInfo),
         );
         const blobUrl = URL.createObjectURL(blob);
         if (cancelled) {
@@ -90,7 +86,6 @@ function useDecryptedMediaUrl(
     };
   }, [mx, mxcUrl, encInfo, useAuthentication, mimeType]);
 
-  // Revoke blob URL when the component unmounts
   useEffect(
     () => () => {
       if (prevBlobUrl.current) URL.revokeObjectURL(prevBlobUrl.current);
@@ -101,18 +96,47 @@ function useDecryptedMediaUrl(
   return state;
 }
 
+// ── Helpers ───────────────────────────────────────────────────────────────────
+
+function formatRelativeDate(ts: number): string {
+  const diff = Date.now() - ts;
+  const mins = Math.floor(diff / 60000);
+  if (mins < 2) return 'Just now';
+  if (mins < 60) return `${mins}m ago`;
+  const hrs = Math.floor(diff / 3600000);
+  if (hrs < 24) return `${hrs}h ago`;
+  const days = Math.floor(diff / 86400000);
+  if (days < 7) return `${days}d ago`;
+  return new Date(ts).toLocaleDateString(undefined, { month: 'short', day: 'numeric' });
+}
+
+function formatBytes(bytes: number): string {
+  if (bytes < 1024) return `${bytes} B`;
+  if (bytes < 1048576) return `${(bytes / 1024).toFixed(1)} KB`;
+  return `${(bytes / 1048576).toFixed(1)} MB`;
+}
+
+function monthLabel(ts: number): string {
+  return new Date(ts).toLocaleDateString(undefined, { month: 'long', year: 'numeric' });
+}
+
+function getSenderName(room: Room, userId: string): string {
+  return room.getMember(userId)?.name ?? userId.split(':')[0]?.slice(1) ?? userId;
+}
+
 // ── Lightbox ──────────────────────────────────────────────────────────────────
 
 type LightboxItem = {
   mxcUrl: string;
   encInfo?: IEncryptedFile;
   mimeType?: string;
+  msgtype: MsgType.Image | MsgType.Video;
   body: string;
   sender: string;
   ts: number;
 };
 
-function LightboxImage({
+function LightboxMedia({
   item,
   useAuthentication,
 }: {
@@ -135,7 +159,14 @@ function LightboxImage({
       justifyContent="Center"
       style={{ height: '100%', gap: config.space.S200 }}
     >
-      {media.status === 'loading' && <Spinner size="600" />}
+      {media.status === 'loading' && (
+        <Box direction="Column" alignItems="Center" gap="200">
+          <Spinner size="600" />
+          <Text size="T300" priority="300">
+            {item.encInfo ? 'Decrypting…' : 'Loading…'}
+          </Text>
+        </Box>
+      )}
       {media.status === 'error' && (
         <Box direction="Column" alignItems="Center" gap="200">
           <Icon src={Icons.Warning} size="600" />
@@ -144,19 +175,34 @@ function LightboxImage({
           </Text>
         </Box>
       )}
-      {media.status === 'ok' && (
+      {media.status === 'ok' &&
-        <img
+        (item.msgtype === MsgType.Video ? (
-          src={media.url}
+          // eslint-disable-next-line jsx-a11y/media-has-caption
-          alt={item.body}
+          <video
-          style={{
+            src={media.url}
-            maxWidth: '100%',
+            controls
-            maxHeight: 'calc(100vh - 120px)',
+            autoPlay
-            objectFit: 'contain',
+            style={{
-            borderRadius: config.radii.R300,
+              maxWidth: '100%',
-            display: 'block',
+              maxHeight: 'calc(100vh - 120px)',
-          }}
+              borderRadius: config.radii.R300,
-        />
+              display: 'block',
-      )}
+              background: '#000',
+            }}
+          />
+        ) : (
+          <img
+            src={media.url}
+            alt={item.body}
+            style={{
+              maxWidth: '100%',
+              maxHeight: 'calc(100vh - 120px)',
+              objectFit: 'contain',
+              borderRadius: config.radii.R300,
+              display: 'block',
+            }}
+          />
+        ))}
     </Box>
   );
 }
@@ -191,8 +237,7 @@ function Lightbox({
   const item = items[index];
   if (!item) return null;
 
-  const date = new Date(item.ts);
+  const dateStr = new Date(item.ts).toLocaleDateString(undefined, {
-  const dateStr = date.toLocaleDateString(undefined, {
     month: 'short',
     day: 'numeric',
     year: 'numeric',
@@ -203,7 +248,7 @@ function Lightbox({
     <div
       role="dialog"
       aria-modal
-      aria-label="Image viewer"
+      aria-label="Media viewer"
       onKeyDown={handleKeyDown}
       tabIndex={-1}
       style={{
@@ -215,19 +260,19 @@ function Lightbox({
         flexDirection: 'column',
       }}
     >
-      {/* Top bar */}
+      {/* Header bar */}
       <Box
         alignItems="Center"
         gap="200"
         style={{
           padding: `${config.space.S200} ${config.space.S300}`,
-          borderBottom: `1px solid rgba(255,255,255,0.08)`,
+          borderBottom: '1px solid rgba(255,255,255,0.08)',
           flexShrink: 0,
         }}
       >
         <Box grow="Yes" direction="Column" style={{ overflow: 'hidden' }}>
           <Text size="T400" truncate style={{ color: '#fff', fontWeight: 500 }}>
-            {item.body || 'Image'}
+            {item.body || (item.msgtype === MsgType.Video ? 'Video' : 'Image')}
           </Text>
           <Text size="T200" style={{ color: 'rgba(255,255,255,0.5)' }}>
             {item.sender} · {dateStr}
@@ -247,14 +292,14 @@ function Lightbox({
           }
         >
           {(ref) => (
-            <IconButton ref={ref} variant="Surface" aria-label="Close lightbox" onClick={onClose}>
+            <IconButton ref={ref} variant="Surface" aria-label="Close" onClick={onClose}>
               <Icon src={Icons.Cross} />
             </IconButton>
           )}
         </TooltipProvider>
       </Box>
 
-      {/* Image area */}
+      {/* Media area with nav arrows */}
       <Box
         grow="Yes"
         alignItems="Center"
@@ -264,7 +309,7 @@ function Lightbox({
         {index > 0 && (
           <IconButton
             variant="Surface"
-            aria-label="Previous image"
+            aria-label="Previous"
             onClick={prev}
             style={{ flexShrink: 0, marginRight: config.space.S200 }}
           >
@@ -277,7 +322,7 @@ function Lightbox({
           justifyContent="Center"
           style={{ overflow: 'hidden', height: '100%' }}
         >
-          <LightboxImage
+          <LightboxMedia
             key={`${item.mxcUrl}-${item.ts}`}
             item={item}
             useAuthentication={useAuthentication}
@@ -286,7 +331,7 @@ function Lightbox({
         {index < items.length - 1 && (
           <IconButton
             variant="Surface"
-            aria-label="Next image"
+            aria-label="Next"
             onClick={next}
             style={{ flexShrink: 0, marginLeft: config.space.S200 }}
           >
@@ -298,12 +343,13 @@ function Lightbox({
   );
 }
 
-// ── Thumbnail tile ─────────────────────────────────────────────────────────────
+// ── Gallery tile ──────────────────────────────────────────────────────────────
 
 function GalleryTile({
   mxcUrl,
   encInfo,
   mimeType,
+  isVideo,
   body,
   sender,
   ts,
@@ -313,6 +359,7 @@ function GalleryTile({
   mxcUrl: string;
   encInfo?: IEncryptedFile;
   mimeType?: string;
+  isVideo: boolean;
   body: string;
   sender: string;
   ts: number;
@@ -320,17 +367,14 @@ function GalleryTile({
   onClick: () => void;
 }) {
   const mx = useMatrixClient();
-
-  // For thumbnails: prefer encrypted thumbnail if present, else use full image
   const media = useDecryptedMediaUrl(mx, mxcUrl, encInfo, useAuthentication, mimeType);
-
   const [hovered, setHovered] = useState(false);
   const relDate = formatRelativeDate(ts);
 
   return (
     <button
       type="button"
-      aria-label={body || 'Image'}
+      aria-label={body || (isVideo ? 'Video' : 'Image')}
       onClick={onClick}
       onMouseEnter={() => setHovered(true)}
       onMouseLeave={() => setHovered(false)}
@@ -357,13 +401,13 @@ function GalleryTile({
           gap="100"
           style={{ padding: config.space.S100 }}
         >
-          <Icon src={Icons.Photo} size="300" />
+          <Icon src={isVideo ? Icons.Play : Icons.Photo} size="300" />
           <Text
             size="T200"
             truncate
             style={{ maxWidth: '100%', textAlign: 'center', opacity: 0.5 }}
           >
-            {body || 'Image'}
+            {body}
           </Text>
         </Box>
       )}
@@ -374,13 +418,36 @@ function GalleryTile({
           style={{ width: '100%', height: '100%', objectFit: 'cover', display: 'block' }}
         />
       )}
+
+      {/* Video play badge */}
+      {isVideo && media.status === 'ok' && (
+        <div
+          style={{
+            position: 'absolute',
+            top: '50%',
+            left: '50%',
+            transform: 'translate(-50%, -50%)',
+            width: 28,
+            height: 28,
+            borderRadius: '50%',
+            background: 'rgba(0,0,0,0.6)',
+            display: 'flex',
+            alignItems: 'center',
+            justifyContent: 'center',
+            pointerEvents: 'none',
+          }}
+        >
+          <Icon src={Icons.Play} size="200" />
+        </div>
+      )}
+
       {/* Hover overlay */}
       {hovered && media.status === 'ok' && (
         <div
           style={{
             position: 'absolute',
             inset: 0,
-            background: 'linear-gradient(to top, rgba(0,0,0,0.75) 0%, transparent 50%)',
+            background: 'linear-gradient(to top, rgba(0,0,0,0.72) 0%, transparent 55%)',
             pointerEvents: 'none',
           }}
         >
@@ -406,28 +473,46 @@ function GalleryTile({
   );
 }
 
-// ── Helpers ───────────────────────────────────────────────────────────────────
+// ── Month separator ───────────────────────────────────────────────────────────
 
-function formatRelativeDate(ts: number): string {
+function MonthSeparator({ label }: { label: string }) {
-  const now = Date.now();
+  return (
-  const diff = now - ts;
+    <Box
-  const mins = Math.floor(diff / 60000);
+      alignItems="Center"
-  if (mins < 60) return mins <= 1 ? 'Just now' : `${mins}m ago`;
+      gap="200"
-  const hrs = Math.floor(diff / 3600000);
+      style={{ padding: `${config.space.S100} 0`, gridColumn: '1 / -1' }}
-  if (hrs < 24) return `${hrs}h ago`;
+    >
-  const days = Math.floor(diff / 86400000);
+      <div style={{ flex: 1, height: 1, background: color.Surface.ContainerLine }} />
-  if (days < 7) return `${days}d ago`;
+      <Text size="T200" priority="300" style={{ flexShrink: 0, whiteSpace: 'nowrap' }}>
-  return new Date(ts).toLocaleDateString(undefined, { month: 'short', day: 'numeric' });
+        {label}
+      </Text>
+      <div style={{ flex: 1, height: 1, background: color.Surface.ContainerLine }} />
+    </Box>
+  );
 }
 
-function formatBytes(bytes: number): string {
+// ── Tab button ────────────────────────────────────────────────────────────────
-  if (bytes < 1024) return `${bytes} B`;
-  if (bytes < 1048576) return `${(bytes / 1024).toFixed(1)} KB`;
-  return `${(bytes / 1048576).toFixed(1)} MB`;
-}
 
-function getSenderDisplayName(room: Room, userId: string): string {
+function TabButton({
-  return room.getMember(userId)?.name ?? userId.split(':')[0]?.slice(1) ?? userId;
+  label,
+  active,
+  onClick,
+}: {
+  label: string;
+  active: boolean;
+  onClick: () => void;
+}) {
+  return (
+    <Button
+      size="300"
+      variant={active ? 'Primary' : 'Secondary'}
+      fill={active ? 'Soft' : 'None'}
+      radii="300"
+      onClick={onClick}
+    >
+      <Text size="B300">{label}</Text>
+    </Button>
+  );
 }
 
 // ── Main component ────────────────────────────────────────────────────────────
@@ -445,22 +530,31 @@ export function MediaGallery({ room, onClose }: MediaGalleryProps) {
   const [loading, setLoading] = useState(false);
   const [hasLoadedOnce, setHasLoadedOnce] = useState(false);
   const [canLoadMore, setCanLoadMore] = useState(true);
+  const [loadError, setLoadError] = useState(false);
   const [lightboxIndex, setLightboxIndex] = useState<number | null>(null);
+  const sentinelRef = useRef<HTMLDivElement>(null);
+
+  const handleTabChange = useCallback((t: GalleryTab) => {
+    setTab(t);
+    setLightboxIndex(null); // stale index would open wrong item in new tab's lightboxItems
+  }, []);
 
   const msgtype = TAB_MSGTYPES[tab];
 
-  const getFilteredEvents = useCallback((): MatrixEvent[] => {
+  const getFilteredEvents = useCallback(
-    const timeline = room.getLiveTimeline();
+    (): MatrixEvent[] =>
-    return timeline
+      room
-      .getEvents()
+        .getLiveTimeline()
-      .filter((ev) => {
+        .getEvents()
-        if (ev.isRedacted()) return false;
+        .filter((ev) => {
-        const c = ev.getContent();
+          if (ev.isRedacted()) return false;
-        return ev.getType() === EventType.RoomMessage && c.msgtype === msgtype;
+          const c = ev.getContent();
-      })
+          return ev.getType() === EventType.RoomMessage && c.msgtype === msgtype;
-      .slice()
+        })
-      .reverse();
+        .slice()
-  }, [room, msgtype]);
+        .reverse(),
+    [room, msgtype],
+  );
 
   const [events, setEvents] = useState<MatrixEvent[]>(() => getFilteredEvents());
 
@@ -468,24 +562,46 @@ export function MediaGallery({ room, onClose }: MediaGalleryProps) {
     setEvents(getFilteredEvents());
     setCanLoadMore(true);
     setHasLoadedOnce(false);
+    setLoadError(false);
   }, [getFilteredEvents]);
 
   const handleLoadMore = useCallback(async () => {
+    if (loading || !canLoadMore) return;
     setLoading(true);
+    setLoadError(false);
     try {
-      const timeline = room.getLiveTimeline();
+      const hasMore = await mx.paginateEventTimeline(room.getLiveTimeline(), {
-      const hasMore = await mx.paginateEventTimeline(timeline, { backwards: true, limit: 100 });
+        backwards: true,
+        limit: 100,
+      });
       setEvents(getFilteredEvents());
       setCanLoadMore(hasMore);
       setHasLoadedOnce(true);
     } catch {
-      // silently swallow
+      // Stop auto-retry: the sentinel would keep firing on every render otherwise.
+      // The user can retry manually via the button shown in the error state.
+      setLoadError(true);
     } finally {
       setLoading(false);
     }
-  }, [mx, room, getFilteredEvents]);
+  }, [loading, canLoadMore, mx, room, getFilteredEvents]);
 
-  // Build lightbox items from current image/video events
+  // Auto-load when sentinel scrolls into view
+  useEffect(() => {
+    const sentinel = sentinelRef.current;
+    if (!sentinel || !canLoadMore || loading) return;
+
+    const observer = new IntersectionObserver(
+      ([entry]) => {
+        if (entry?.isIntersecting) handleLoadMore();
+      },
+      { threshold: 0.1 },
+    );
+    observer.observe(sentinel);
+    return () => observer.disconnect();
+  }, [canLoadMore, loading, handleLoadMore]);
+
+  // Lightbox items (images + videos, flat)
   const lightboxItems: LightboxItem[] = events
     .filter((ev) => {
       const c = ev.getContent();
@@ -494,18 +610,30 @@ export function MediaGallery({ room, onClose }: MediaGalleryProps) {
     .map((ev) => {
       const c = ev.getContent();
       const isEnc = !!c.file;
-      const info: (IImageInfo & IThumbnailContent) | undefined = c.info;
-      const mxcUrl: string = c.file?.url ?? c.url ?? '';
       return {
-        mxcUrl,
+        mxcUrl: c.file?.url ?? c.url ?? '',
         encInfo: isEnc ? c.file : undefined,
-        mimeType: info?.mimetype ?? c.info?.mimetype,
+        mimeType: c.info?.mimetype,
+        msgtype: c.msgtype as MsgType.Image | MsgType.Video,
         body: c.body ?? '',
-        sender: getSenderDisplayName(room, ev.getSender() ?? ''),
+        sender: getSenderName(room, ev.getSender() ?? ''),
         ts: ev.getTs(),
       };
     });
 
+  // Group image/video events by month for the grid
+  type MonthGroup = { label: string; events: MatrixEvent[] };
+  const monthGroups: MonthGroup[] = [];
+  let currentLabel = '';
+  for (const ev of events) {
+    const label = monthLabel(ev.getTs());
+    if (label !== currentLabel) {
+      currentLabel = label;
+      monthGroups.push({ label, events: [] });
+    }
+    monthGroups[monthGroups.length - 1]!.events.push(ev);
+  }
+
   return (
     <>
       <Box
@@ -564,31 +692,27 @@ export function MediaGallery({ room, onClose }: MediaGalleryProps) {
           </Box>
         </Header>
 
-        {/* Tab bar */}
+        {/* Tabs */}
         <Box
           shrink="No"
           gap="100"
           style={{ padding: `${config.space.S200} ${config.space.S200} 0` }}
         >
           {(Object.keys(TAB_LABELS) as GalleryTab[]).map((t) => (
-            <Button
+            <TabButton
               key={t}
-              size="300"
+              label={TAB_LABELS[t]}
-              variant={tab === t ? 'Primary' : 'Secondary'}
+              active={tab === t}
-              fill={tab === t ? 'Soft' : 'None'}
+              onClick={() => handleTabChange(t)}
-              radii="300"
+            />
-              onClick={() => setTab(t)}
-            >
-              <Text size="B300">{TAB_LABELS[t]}</Text>
-            </Button>
           ))}
         </Box>
 
         {/* Content */}
         <Box grow="Yes" style={{ position: 'relative', overflow: 'hidden' }}>
           <Scroll variant="Background" size="300" visibility="Hover" hideTrack>
-            <Box direction="Column" gap="200" style={{ padding: config.space.S200 }}>
+            <Box direction="Column" style={{ padding: config.space.S200, gap: 0 }}>
-              {/* Image / video grid */}
+              {/* ── Image / video grid ── */}
               {(tab === 'image' || tab === 'video') && (
                 <>
                   {events.length === 0 && !loading && (
@@ -598,7 +722,7 @@ export function MediaGallery({ room, onClose }: MediaGalleryProps) {
                       gap="200"
                       style={{ padding: config.space.S400 }}
                     >
-                      <Icon src={Icons.Photo} size="600" />
+                      <Icon src={tab === 'video' ? Icons.Play : Icons.Photo} size="600" />
                       <Text size="T300" priority="300" align="Center">
                         {hasLoadedOnce
                           ? `No ${TAB_LABELS[tab].toLowerCase()} found.`
@@ -606,50 +730,69 @@ export function MediaGallery({ room, onClose }: MediaGalleryProps) {
                       </Text>
                     </Box>
                   )}
-                  {events.length > 0 && (
+
-                    <div
+                  {/* Month groups */}
-                      style={{
+                  {(() => {
-                        display: 'grid',
+                    let flatIdx = 0;
-                        gridTemplateColumns: 'repeat(3, 1fr)',
+                    return monthGroups.map((group) => (
-                        gap: config.space.S100,
+                      <Box
-                      }}
+                        key={group.label}
-                    >
+                        direction="Column"
-                      {events.map((mEvent, idx) => {
+                        style={{ marginBottom: config.space.S200 }}
-                        const c = mEvent.getContent();
+                      >
-                        const isEnc = !!c.file;
+                        {/* Month header — only shown when there are multiple groups */}
-                        const info: (IImageInfo & IThumbnailContent) | undefined = c.info;
+                        {monthGroups.length > 1 && <MonthSeparator label={group.label} />}
-                        // For thumbnails: prefer thumbnail_file > file; for non-enc: use thumbnail URL
+                        <div
-                        const thumbMxc: string | undefined = isEnc
+                          style={{
-                          ? (info?.thumbnail_file?.url ?? c.file?.url)
+                            display: 'grid',
-                          : (info?.thumbnail_url ?? c.url);
+                            gridTemplateColumns: 'repeat(3, 1fr)',
-                        const thumbEncInfo: IEncryptedFile | undefined = isEnc
+                            gap: config.space.S100,
-                          ? (info?.thumbnail_file ?? c.file)
+                          }}
-                          : undefined;
+                        >
-                        const mimeType: string | undefined =
+                          {group.events.map((mEvent) => {
-                          info?.thumbnail_file != null
+                            const c = mEvent.getContent();
-                            ? (info.thumbnail_info?.mimetype ?? 'image/jpeg')
+                            const isEnc = !!c.file;
-                            : (info?.mimetype ?? c.info?.mimetype);
+                            const isVideo = c.msgtype === MsgType.Video;
-                        if (!thumbMxc) return null;
+                            const info: (IImageInfo & IThumbnailContent) | undefined = c.info;
-                        return (
+
-                          <GalleryTile
+                            // Prefer thumbnail_file (encrypted thumb) > file > thumbnail_url > url
-                            key={mEvent.getId()}
+                            const thumbMxc: string | undefined = isEnc
-                            mxcUrl={thumbMxc}
+                              ? (info?.thumbnail_file?.url ?? c.file?.url)
-                            encInfo={thumbEncInfo}
+                              : (info?.thumbnail_url ?? c.url);
-                            mimeType={mimeType}
+                            const thumbEnc: IEncryptedFile | undefined = isEnc
-                            body={c.body ?? ''}
+                              ? (info?.thumbnail_file ?? c.file)
-                            sender={getSenderDisplayName(room, mEvent.getSender() ?? '')}
+                              : undefined;
-                            ts={mEvent.getTs()}
+                            const thumbMime: string | undefined =
-                            useAuthentication={useAuthentication}
+                              info?.thumbnail_file != null
-                            onClick={() => setLightboxIndex(idx)}
+                                ? (info.thumbnail_info?.mimetype ?? 'image/jpeg')
-                          />
+                                : (info?.mimetype ?? 'image/jpeg');
-                        );
+
-                      })}
+                            // Guard before incrementing: skipped tiles must not consume a slot
-                    </div>
+                            if (!thumbMxc) return null;
-                  )}
+                            const idx = flatIdx++;
+                            return (
+                              <GalleryTile
+                                key={mEvent.getId()}
+                                mxcUrl={thumbMxc}
+                                encInfo={thumbEnc}
+                                mimeType={thumbMime}
+                                isVideo={isVideo}
+                                body={c.body ?? ''}
+                                sender={getSenderName(room, mEvent.getSender() ?? '')}
+                                ts={mEvent.getTs()}
+                                useAuthentication={useAuthentication}
+                                onClick={() => setLightboxIndex(idx)}
+                              />
+                            );
+                          })}
+                        </div>
+                      </Box>
+                    ));
+                  })()}
                 </>
               )}
 
-              {/* File list */}
+              {/* ── File list ── */}
               {tab === 'file' && (
                 <>
                   {events.length === 0 && !loading && (
@@ -671,7 +814,7 @@ export function MediaGallery({ room, onClose }: MediaGalleryProps) {
                       const mxcUrl: string | undefined = c.file?.url ?? c.url;
                       const body: string = c.body ?? 'Unnamed file';
                       const size: number | undefined = c.info?.size;
-                      const sender = getSenderDisplayName(room, mEvent.getSender() ?? '');
+                      const sender = getSenderName(room, mEvent.getSender() ?? '');
                       const downloadUrl = mxcUrl
                         ? (mxcUrlToHttp(mx, mxcUrl, useAuthentication) ?? '#')
                         : '#';
@@ -724,14 +867,22 @@ export function MediaGallery({ room, onClose }: MediaGalleryProps) {
                 </>
               )}
 
-              {/* Load more / spinner */}
+              {/* ── Pagination status / sentinel ── */}
               {loading && (
-                <Box justifyContent="Center" style={{ padding: config.space.S200 }}>
+                <Box justifyContent="Center" style={{ padding: config.space.S300 }}>
                   <Spinner />
                 </Box>
               )}
-              {!loading && canLoadMore && (
+              {loadError && !loading && (
-                <Box justifyContent="Center" style={{ padding: `${config.space.S100} 0` }}>
+                <Box
+                  direction="Column"
+                  alignItems="Center"
+                  gap="200"
+                  style={{ padding: config.space.S300 }}
+                >
+                  <Text size="T200" priority="300" align="Center">
+                    Failed to load history.
+                  </Text>
                   <Button
                     size="300"
                     variant="Secondary"
@@ -739,20 +890,24 @@ export function MediaGallery({ room, onClose }: MediaGalleryProps) {
                     radii="300"
                     onClick={handleLoadMore}
                   >
-                    <Text size="B300">Load More History</Text>
+                    <Text size="B300">Retry</Text>
                   </Button>
                 </Box>
               )}
-              {!loading && !canLoadMore && hasLoadedOnce && (
+              {!loading && !loadError && !canLoadMore && hasLoadedOnce && events.length > 0 && (
                 <Text
                   size="T200"
                   priority="300"
                   align="Center"
-                  style={{ padding: `${config.space.S100} 0` }}
+                  style={{ padding: `${config.space.S200} 0` }}
                 >
                   Beginning of history
                 </Text>
               )}
+              {/* IntersectionObserver sentinel — only rendered when safe to auto-trigger */}
+              {canLoadMore && !loading && !loadError && (
+                <div ref={sentinelRef} style={{ height: 1 }} />
+              )}
             </Box>
           </Scroll>
         </Box>