Files missing from trace, cache not invalidated

[zopsicle]

$ cached-nix-shell --version     
cached-nix-shell v0.1.6
Using /nix/store/w4l4xvw461ywc4ia3accj5i3hh50n4r8-nix-2.24.10/bin/nix-shell
nix-shell (Nix) 2.24.10
$ echo '(import <nixpkgs> {}).mkShell {}' > shell.nix
$ cached-nix-shell --pure --run :
cached-nix-shell: updating cache
cached-nix-shell: done in 578.051974ms

Then:

$ echo > shell.nix
$ cached-nix-shell --pure --run :
$ echo $?
0

should instead have invalidated cache and subsequently failed with Nix error: syntax error, unexpected end of file.

$ cat ~/.cache/cached-nix-shell/64155d6fb1607858b3c0e0c0f2891067f9b4603f0f3f150e7d1b8a5c991c9c31.trace

Observe that shell.nix is listed as s FILENAME \0 + \0, not as f FILENAME \0 b3sum(file contents) \0.