[vbmithr]

Downloaded Discord images failed to display on Linux/Windows because media cache filenames are extensionless hashes, while the still-image decoder selected the format from the filename. The error tooltip also let its text extend beyond its background.

Detect image formats from their bytes, as the avatar decoder already does, and prevent thumbnail decoding from enlarging a smaller source. Give tooltip text a shrinking, wrapping flex slot within the 240px box while keeping shortcut labels on one line. Update the system and media design specifications.

Validation:

• The extensionless cache regression failed before the fix and passes for PNG, JPEG, and WebP afterwards.
• The existing thumbnail sizing/cropping regression now passes; previously it enlarged a 64×32 BMP to 4096×2048 against its documented contract.
• Full GUI-feature tests pass on the PR base.
• Arch package revision 18 built successfully; the user confirmed the previously reported image now loads.
• git diff --check passes. Tooltip wrapping was not visually verified after the change.

[itz4blitz]

Cache files have no extension, and ImageReader::with_guessed_format reads the bytes the way the macOS path already does. The thumbnail edge is now capped at the source's long side, so a small picture is no longer scaled up to the requested size. The tooltip text sits in a shrinking flex slot inside the 240-point box, and the shortcut stays on one line. macOS, Linux, and Windows are green on 2d1d7e1.