Improve timeline scroll, media layout, avatars, and emoji coverage.

Remember room scroll position across switches, reserve image/video heights from Matrix dimensions, cache authenticated media blobs for avatars, restore jumbo emoji-only messages, and extend emoji font unicode-range for Unicode 15 glyphs.

src/app/components/room-avatar/RoomAvatar.tsx

@@ -1,13 +1,23 @@
 import { JoinRule } from 'matrix-js-sdk';
 import { AvatarFallback, AvatarImage, color } from 'folds';
 import { Icon, Icons } from '../icons';
-import React, { ComponentProps, ReactEventHandler, ReactNode, forwardRef, useState } from 'react';
+import React, { ComponentProps, ReactEventHandler, ReactNode, forwardRef, useEffect, useState } from 'react';
+import { Blurhash } from 'react-blurhash';
 import * as css from './RoomAvatar.css';
 import { joinRuleToIconSrc } from '../../utils/room';
 import colorMXID from '../../../util/colorMXID';
 import { useAuthenticatedMediaUrl } from '../../hooks/useAuthenticatedMediaUrl';
 import { useMediaAuthentication } from '../../hooks/useMediaAuthentication';
 import { cacheAvatar, isAvatarCached, pruneAvatarCache } from '../../utils/avatarCache';
+import {
+  getCachedAuthenticatedMediaUrl,
+  isAuthenticatedMediaUrl,
+} from '../../utils/authenticatedMediaCache';
+import {
+  getMediaBlurHash,
+  getMediaDimensions,
+  rememberMediaBlurHash,
+} from '../../state/mediaDimensionCache';
 
 type RoomAvatarProps = {
   roomId: string;
@@ -17,19 +27,36 @@ type RoomAvatarProps = {
 };
 export function RoomAvatar({ roomId, src, alt, renderFallback }: RoomAvatarProps) {
   const [error, setError] = useState(false);
-  const [loaded, setLoaded] = useState(() => isAvatarCached(src));
   const useAuthentication = useMediaAuthentication();
   const authenticatedSrc = useAuthenticatedMediaUrl(src, useAuthentication);
+  const blurHash = getMediaBlurHash(src ?? '');
+  const dims = getMediaDimensions(src ?? '');
+  const blobCached =
+    !!src &&
+    (!useAuthentication ||
+      !isAuthenticatedMediaUrl(src) ||
+      !!getCachedAuthenticatedMediaUrl(src));
+  const [loaded, setLoaded] = useState(() => isAvatarCached(src) || blobCached);
+
+  useEffect(() => {
+    if (
+      authenticatedSrc &&
+      (isAvatarCached(src) ||
+        (src && (!useAuthentication || !isAuthenticatedMediaUrl(src) || getCachedAuthenticatedMediaUrl(src))))
+    ) {
+      setLoaded(true);
+    }
+  }, [authenticatedSrc, src, useAuthentication]);
 
   const handleLoad: ReactEventHandler<HTMLImageElement> = (evt) => {
     evt.currentTarget.setAttribute('data-image-loaded', 'true');
     setLoaded(true);
     cacheAvatar(src);
     pruneAvatarCache();
+    rememberMediaBlurHash(src ?? '', evt.currentTarget);
   };
 
-  // No src or error - show fallback only
-  if (!authenticatedSrc || error) {
+  if (!src || error) {
     return (
       <AvatarFallback
         style={{ backgroundColor: colorMXID(roomId ?? ''), color: color.Surface.Container }}
@@ -40,8 +67,7 @@ export function RoomAvatar({ roomId, src, alt, renderFallback }: RoomAvatarProps
     );
   }
 
-  // If already cached, show image directly without fallback flash
-  if (loaded) {
+  if (authenticatedSrc && loaded) {
     return (
       <AvatarImage
         className={css.RoomAvatar}
@@ -55,12 +81,17 @@ export function RoomAvatar({ roomId, src, alt, renderFallback }: RoomAvatarProps
     );
   }
 
-  // Loading state - render fallback with image overlay
+  const blurResolutionX = 32;
+  const blurResolutionY =
+    dims?.w && dims?.h && dims.w > 0
+      ? Math.max(1, Math.round(blurResolutionX * (dims.h / dims.w)))
+      : 32;
+
   return (
     <div style={{ position: 'relative', width: '100%', height: '100%' }}>
       <AvatarFallback
-        style={{ 
-          backgroundColor: colorMXID(roomId ?? ''), 
+        style={{
+          backgroundColor: colorMXID(roomId ?? ''),
           color: color.Surface.Container,
           position: 'absolute',
           inset: 0,
@@ -69,15 +100,39 @@ export function RoomAvatar({ roomId, src, alt, renderFallback }: RoomAvatarProps
       >
         {renderFallback()}
       </AvatarFallback>
-      <AvatarImage
-        className={css.RoomAvatar}
-        style={{ position: 'relative', zIndex: 1 }}
-        src={authenticatedSrc}
-        alt={alt}
-        onError={() => setError(true)}
-        onLoad={handleLoad}
-        draggable={false}
-      />
+      {blurHash && (
+        <div
+          style={{
+            position: 'absolute',
+            inset: 0,
+            overflow: 'hidden',
+            borderRadius: 'inherit',
+            filter: 'blur(6px)',
+            transform: 'scale(1.08)',
+          }}
+        >
+          <Blurhash
+            hash={blurHash}
+            width="100%"
+            height="100%"
+            resolutionX={blurResolutionX}
+            resolutionY={blurResolutionY}
+            punch={1.1}
+            style={{ display: 'block' }}
+          />
+        </div>
+      )}
+      {authenticatedSrc && (
+        <AvatarImage
+          className={css.RoomAvatar}
+          style={{ position: 'relative', zIndex: 1, opacity: loaded ? 1 : 0 }}
+          src={authenticatedSrc}
+          alt={alt}
+          onError={() => setError(true)}
+          onLoad={handleLoad}
+          draggable={false}
+        />
+      )}
     </div>
   );
 }