Fullscreen / enlarged animated custom emoji is blurry (low-res thumbnail upscaled) #2296

Description

When opening an animated / custom emoji in Telegram’s full-size media viewer, the client shows a blurry, low-quality image. It looks like a small inline thumbnail is being scaled up instead of rendering the full Lottie/.tgs animation (or a high-resolution still) at a crisp large size.

Reported by Hyperlinks Space — tracking: HyperlinksSpace/HyperlinksSpaceProgram#92
Write-up: https://github.com/HyperlinksSpace/HyperlinksSpaceProgram/blob/docs/telegram-emoji-fullscreen-quality/docs/telegram-upstream/animated-emoji-fullscreen-quality.md

Steps to reproduce

1. Open a chat that contains an animated / custom emoji (or emoji status / pack preview that opens in the media viewer).
2. Tap / click the emoji to open it full size in the media viewer.
3. Observe the enlarged image.

Expected behaviour

The fullscreen view should play the vector/Lottie animation crisply, or show a high-resolution asset suitable for large display (HiDPI-aware).

Actual behaviour

The viewer enlarges a small raster preview. Edges are jagged and the image looks soft/pixelated.

Screenshot

Suggested direction

When opening custom/animated emoji in the media viewer, prefer the document / animation (or largest available preview) over the inline emoji cache thumbnail. Avoid treating this path as a generic photo open that sticks to the smallest cached bitmap.

Environment

• Observed on Telegram Desktop (Windows) media viewer (“Photo N of M” style chrome).
• Please confirm whether the same thumbnail-upscale path exists on this client.

Related

• Possibly related to large emoji Retina quality: Large single emoji looks oversized and blurry on Retina (3×) displays #2292