udisksctl: get loop device and mount point without resorting to parsing localized output?

udisksctl is my tool of choice when dealing with file system images ([recent example](https://unix.stackexchange.com/questions/775274/create-fat-formatted-disk-image-that-can-fit-1g-file/775277#775277) , but I've been doing this [all over the place](https://unix.stackexchange.com/search?q=user%3A106650+udisksctl+is%3Aanswer)) . The dance typically looks like

fallocate -l ${img_size} filesystem.img
mkfs.${fs} filesystem.img

# Set up loop device as regular user
loopback=$(udisksctl loop-setup -b "${img_file}" | sed 's/.* \([^ ]*\)\.$/\1/')

# Mount as regular user
mounted=$(udisksctl mount -b "${loopback}" | sed 's/^.* \([^ ]*\)$/\1/')

# Do the testing/benchmarking/file management
# e.g.:
cp -- "${files[@]}" "${mounted}"

Quite frankly, I have a bad feeling about the way I parse the output of udisksctl; these are clearly human-aimed strings: >

> Mapped file filesystem.img as /dev/loop0.
> Mounted /dev/loop1 at /run/media/marcus/E954-81FB
>

And I don't think anyone considers their actual format "API". So, my scripts might break in the future! (Not to mention the nasal demons I invite if the image file name contains line breaks.) udisksctl doesn't seem to have a "porcelain" output option or similar. Is there an existing method that does udisksctl's job of loopback mounting with user privilege through udisks2, with a proper, unambiguous output?