Context (and thanks for the help in that thread) https://lemmy.world/post/48690873
It's been a week since I seriously injured that snail. The day after the injury I returned with a plastic box you might get a pair of boots in and put 1-2cm of soil from the surrounding area into it. I added leaves for shelter, some calcium carbonate, moisture and daily replacement of fresh greens.
Just before I moved her to the box, she had been trying but failing to climb over a small wooden log (for about an hour). Her tentacles seemed perfectly straight so I assumed she was somewhat healthy.
I scooped her up gently with a pair of playing cards and added her to the box. When I got home, which was a 5 minute walk, there was no sign of her besides her broken shell. I'm assuming she borrowed slightly into the soil or took shelter under the leaves.

She's shaded and sheltered now. Curiously, I've noticed some days when I replace the food, the previous day's food has a few nibbles in it (see pics 1 & 2). So something is eating. There were other tiny creatures in the soil that I couldn't entirely shake off.
From what I've read online the smell of a dead snail is unmistakeable, but since this box is outdoors (although well sheltered) I wonder if I'd notice. For now I'll keep an eye and try to maintain fresh food and humidity. I assume that if she's still alive, she'll emerge when she's ready.
I can't tell what's in the box now (pic 3) and I'm afraid to disturb anything. Thanks to everyone for the advice and encouragement so far!