Terminal directory only updated on `cd`, causes problems with subshells

Fish updates the terminal's notion of the current directory every time I run `cd`, but it doesn't seem to update it any other time. This is a problem if I run a subshell and change the directory there, because upon exiting the subshell, the terminal continues to believe we're in the wrong directory.

For comparison, the system configuration for bash on macOS has it update the terminal directory as part of the `PROMPT_COMMAND` (for login shells). This means the moment I exit the subshell, it'll inform the terminal what the correct directory is.

Reproduced with fish 3.0.2.