Index: src/services/ThumbnailService.js
===================================================================
--- src/services/ThumbnailService.js	(revision 5bc67b493c1987f2d7e3261858e8b8c9739a19b5)
+++ src/services/ThumbnailService.js	(revision 7475ff3132b7044bdc1bf9541e5686fbbc3eadbf)
@@ -24,7 +24,8 @@
 
 // Allowed widths (whitelist → no arbitrary-size abuse). 96 = small feed/comment avatars
-// (~44px); 128 = nav/profile avatars; 256 ≈ 2× a list cover; 480 ≈ 2× a grid tile. Keep
-// these ~2× the display size so line-art stays crisp (the browser barely downscales).
-export const THUMB_SIZES = new Set([96, 128, 256, 320, 480, 640]);
+// (~44px); 128 = nav/profile avatars; 256 ≈ 2× a list cover; 480 ≈ 2× a grid tile; 1280 =
+// full-width timeline media (crisp on mobile retina, ~430px × 3 DPR). Keep these ~2× the
+// display size so the browser barely scales (avoids both jaggies and upscaling blur).
+export const THUMB_SIZES = new Set([96, 128, 256, 320, 480, 640, 1280]);
 
 let _seq = 0;