https://github.com/torvalds/linux/blob/v6.17/fs/binfmt_scrip...
I think it makes it to calling open_exec but there's a test for BINPRM_FLAGS_PATH_INACCESSIBLE, which doesn't seem relevant since 'bash' isn't like '/dev/fd/<fd>/..', but does provoke an ENOENT.
https://github.com/torvalds/linux/blob/v6.17/fs/exec.c#L1445
Maybe someone else can explain it, I'd enjoy the details, and ran out of steam.