Texture allocation or usage glitches
At low framerates (or possibly only on web builds) the Animation demo glitches out and displays the wrong texture on a block. We're supposed to prevent this by keeping texture tile handles alive until the mesh is no longer in use, but evidently that isn't happening.
https://github.com/kpreid/all-is-cubes/assets/779501/a1546c0e-32ab-416f-b799-ae9e2af887cb
Commit 9e723292fe695d633c6a1fc011114efa2d21ba21 adds overwriting deallocated texels; this color does appear for some animation frames, showing that the problem is indeed that meshes are outliving tiles.
It's also possible to trigger this bug by toggling the transparency option (which currently causes all meshes to be rebuilt).