> Looks like there is support in Tiled for optional automatic mirroring or rotations to add missing tile variations.

Tiled uses tile "Global IDs" that encode booleans for flip and rotation into the upper bits: https://doc.mapeditor.org/en/latest/reference/global-tile-id...

It's kind of a pain in the ass to implement IMHO because you need to strip these bits and iterate all of your tilesets to find the correct tileset and tile for the GID for every ID (which is what the tile layers actually store) but a lot of the inherent performance issues can be improved upon by caching the last result, since consecutive tiles in a tilemap are likely to repeat.

Also I found this page useful: https://eishiya.com/articles/tiled/