Found a picture of it and looks like the cap on gandalfs head might not be the mushroom in the meme https://scd.landcareresearch.co.nz/Specimen/PDD 106954
I suspect it was named after gandalf because it seems to live in New Zealand.
It’s not referring to a valve but rather the structures protecting the spore bearing tissue of the mushroom. Bivelangiocarpic means there are two veils protecting the spore bearing tissue until that matures. My source: https://davidmoore.org.uk/21st_century_guidebook_to_fungi_platinum/Ch12_04.htm
I use this approach and there’s never been an unrecoverable situation over the decade plus I’ve used Arch Linux.