Media survive failures: uploaded when attached, the server's limits, alt text asked for

The composer uploads each file as soon as it is attached (streamed from the browser file, under its own ten-minute
timeout), shows it uploading, processing (a 202 followed until ready), ready or failed with Retry, and cancels one
removed; publishing sends the ids, so a failed publish or a retried upload sends nothing twice. Size limits and types
come from /api/v2/instance, a file without a browser type gets one from its extension, and each refusal names the file
and why. Previews are 320 px thumbnails, not whole files in memory. A picture without a description is asked about once
("Publish anyway"; a setting turns it off), descriptions are sent with PUT, and an edit keeps the post's media, language
and sensitive flag.

Profile pictures are checked against the server's types and can be removed. A card shows "Media unavailable" with the
original's link when a picture fails, the blurhash behind a sensitive placeholder, and plays a GIF only on tap under
reduced motion. A failed export says so instead of downloading part of a file.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

Components/Content.razor

@@ -623,9 +623,10 @@
 					<NerdTip Heading="@Localizer["Media"]" Rows="MediaRows(media)" Class="block w-full" TapOpens="false">
 						@if ((status.Sensitive || IsBlurred) && !revealedMedia.Contains(media.Id))
 						{
-							<button type="button" class="flex items-center justify-center w-full aspect-video rounded-lg neo-inset neo-2xs text-sm"
-									@onclick="() => revealedMedia.Add(media.Id)">
-								<i class="ion-md-eye-off mr-2"></i>@(IsBlurred ? Localizer["Filtered media, show"] : Localizer["Sensitive media, show"])
+							@* its blurhash shows behind it: the colours, nothing of what it shows *@
+							<button type="button" class="flex items-center justify-center w-full aspect-video rounded-lg neo-inset neo-2xs text-sm bg-cover"
+									@onclick="() => revealedMedia.Add(media.Id)" data-blurhash="@media.Blurhash">
+								<span class="inline-flex items-center rounded-box bg-base-100/85 px-3 py-1"><i class="ion-md-eye-off mr-2"></i>@(IsBlurred ? Localizer["Filtered media, show"] : Localizer["Sensitive media, show"])</span>
 							</button>
 						}
 						else
@@ -776,22 +777,37 @@
 		}
 	</div>;
 
-	RenderFragment Media(MediaAttachment media, bool several) => media.Type switch
+	// media that didn't load (gone from their server, or refused): said so, with the way to their original
+	HashSet<string> unavailableMedia = [];
+
+	RenderFragment Media(MediaAttachment media, bool several) => unavailableMedia.Contains(media.Id) ? Unavailable(media) : media.Type switch
 	{
 		"image" => @<button type="button" class="block w-full cursor-zoom-in" @onclick="() => OpenPicture(media)"
 								 aria-label="@(media.Description ?? Localizer["Picture"])" data-picture>
 			<img alt="@media.Description" title="@media.Description" loading="lazy" class="w-full rounded-lg object-cover @(several ? "aspect-square" : "max-h-[60vh]")"
-				 src="@(media.PreviewUrl ?? media.Url)" data-blurhash="@media.Blurhash" style="@FocalPoint(media)" />
+				 src="@(media.PreviewUrl ?? media.Url)" data-blurhash="@media.Blurhash" style="@FocalPoint(media)" @onerror="() => unavailableMedia.Add(media.Id)" />
 		</button>,
-		"gifv" => @<video class="w-full rounded-lg" autoplay muted loop playsinline title="@media.Description" src="@media.Url"></video>,
+		// under reduced motion a gifv waits for a tap (its controls)
+		"gifv" => @<video class="w-full rounded-lg" autoplay="@(!CascadingState.Status.PrefersReducedMotion())" controls="@CascadingState.Status.PrefersReducedMotion()" muted loop
+						  playsinline poster="@media.PreviewUrl" title="@media.Description" src="@media.Url" @onerror="() => unavailableMedia.Add(media.Id)"></video>,
 		"video" => @<video class="w-full max-h-[50vh] aspect-video rounded-lg neo-inset neo-2xs" controls playsinline preload="metadata"
-						  poster="@media.PreviewUrl" title="@media.Description" src="@media.Url"></video>,
-		"audio" => @<audio class="w-full" controls preload="metadata" title="@media.Description" src="@media.Url"></audio>,
+						  poster="@media.PreviewUrl" title="@media.Description" src="@media.Url" @onerror="() => unavailableMedia.Add(media.Id)"></video>,
+		"audio" => @<audio class="w-full" controls preload="metadata" title="@media.Description" src="@media.Url" @onerror="() => unavailableMedia.Add(media.Id)"></audio>,
 		_ => @<a class="btn btn-sm justify-start" href="@media.Url" target="_blank" rel="noopener noreferrer">
 			<i class="ion-md-document"></i><span class="truncate">@(media.Description ?? media.Url)</span>
 		</a>
 	};
 
+	RenderFragment Unavailable(MediaAttachment media) =>
+		@<div class="flex flex-col items-center justify-center gap-2 w-full aspect-video rounded-lg neo-inset neo-2xs text-sm" data-media-unavailable>
+			<i class="ion-md-alert text-lg opacity-70" aria-hidden="true"></i>
+			<span>@Localizer["Media unavailable"]</span>
+			@if ((media.RemoteUrl ?? media.Url) is { Length: > 0 } original)
+			{
+				<a class="link text-xs pointer-coarse:py-3.5" href="@original" target="_blank" rel="noopener noreferrer">@Localizer["Open original"]</a>
+			}
+		</div>;
+
 	async Task Act(StatusAction action)
 	{
 		isActing = true;