The panel decoration was drawn as vector and flattened to a 4KB indexed GIF around 2007, with the panel colour baked in as an opaque backdrop. It has only two colours, one of them byte-identical to the background-color the same element already paints. Refitting its four ellipse boundaries recovers the original geometry, so it goes back to being what it was: two elliptical annuli, 553 bytes of SVG, transparent so it composites over the panel instead of having to match it.

The geometry is fitted, not traced: sub-pixel boundary extraction (the alpha=0.5 crossing between neighbouring pixels, which also uses the sparse anti-aliased pixels) feeding a direct least-squares conic fit, max radial residual 0.57px. Rasterised at the same size, the only pixels that differ from the GIF are single-pixel anti-aliasing fringes along the four boundaries, and none survive a 3x3 erosion of that difference, so no edge has moved. An auto-trace would have produced several KB of bezier soup with the raster wobble baked in.

Test 142 asserted image/gif on the deleted file. That assertion moves to header_title_4.gif, and the new asset gets an image/svg+xml check; svg was already in htsserver's table.

The engine keeps its own embedded copy of this GIF for the backblue.gif it writes into mirrors. That one is untouched: the filename and byte length are a contract with pages already on disk.