Rename dotfiles -> briefcase

Renaming my mono-repo briefcase.

I first introduced this commit in master, but it introduced a bug where one of
two things would happen:

1. Emacs wouldn't start and would crash X.
2. Emacs would start but my keyboard wouldn't work.

I learned some valuable debugging skills in the process. Here are some of them:

When my keyboard was broken, I wanted to control my computer using my
laptop. Thankfully this is possible by using `x2x`, which forward X events from
the SSH client to the SSH host.

```shell
> # I'm unsure if this is the *exact* command
> ssh -X desktop x2x -west :0.0
```

Git commit-local bisecting. I didn't need to do a `git bisect` because I knew
which commit introduced the bug; it was HEAD, master. But -- as you can see from
the size of this commit -- there are many changes involved. I wanted to binary
search through the changes, so I did the following workflow using `magit`:

- git reset --soft HEAD^
- git stash 1/2 of the files changed
- re-run `nix-env -f ~/briefcase/emacs -i`
- restart X session
- If the problem persists, the bug exists in the non-stashed files. Repeat the
  process until you find the bug.

In my case, the bug was pretty benign. Calling `(exwm/switch "Dotfiles")` at the
bottom of `window-manager.el` was failing because "Dotfiles" is the name of a
non-existent workspace; it should've been `(exwm/switch "Briefcase")`.

There may have been more problems. I changed a few other things along the way,
including exposing the env vars BRIEFCASE to `wpcarros-emacs` inside of
`emacs/default.nix`.

The important part is that this was a valuable learning opportunity, and I'm
glad that I'm walking away from the two days of "lost productivity" feeling
actually productive.

emacs/.emacs.d/wpc/wpc-nix.el

@@ -8,8 +8,10 @@
 ;; Dependencies
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
-(prelude/assert (f-exists? "~/universe"))
-(prelude/assert (f-exists? "~/depot"))
+;; TODO: These may fail at startup. How can I make sure that the .envrc is
+;; consulted when Emacs starts?
+(prelude/assert (f-exists? (getenv "BRIEFCASE")))
+(prelude/assert (f-exists? (getenv "DEPOT")))
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; Library
@@ -19,7 +21,7 @@
 (use-package nix-mode
   :mode "\\.nix\\'")
 
-(defun nix/sly-from-universe (attribute)
+(defun nix/sly-from-briefcase (attribute)
   "Start a Sly REPL configured with a Lisp matching a derivation
   from my monorepo.
 
@@ -29,12 +31,12 @@ This function was taken from @tazjin's depot and adapted for my monorepo.
   asynchronously. The build output is included in the error
   thrown on build failures."
   (interactive "sAttribute: ")
-  (lexical-let* ((outbuf (get-buffer-create (format "*universe-out/%s*" attribute)))
-         (errbuf (get-buffer-create (format "*universe-errors/%s*" attribute)))
-         (expression (format "let depot = import <depot> {}; universe = import <universe> {}; in depot.nix.buildLisp.sbclWith [ universe.%s ]" attribute))
+  (lexical-let* ((outbuf (get-buffer-create (format "*briefcase-out/%s*" attribute)))
+         (errbuf (get-buffer-create (format "*briefcase-errors/%s*" attribute)))
+         (expression (format "let depot = import <depot> {}; briefcase = import <briefcase> {}; in depot.nix.buildLisp.sbclWith [ briefcase.%s ]" attribute))
          (command (list "nix-build" "-E" expression)))
-    (message "Acquiring Lisp for <depot>.%s" attribute)
-    (make-process :name (format "depot-nix-build/%s" attribute)
+    (message "Acquiring Lisp for <briefcase>.%s" attribute)
+    (make-process :name (format "nix-build/%s" attribute)
                   :buffer outbuf
                   :stderr errbuf
                   :command command
@@ -45,7 +47,7 @@ This function was taken from @tazjin's depot and adapted for my monorepo.
                           ("finished\n"
                            (let* ((outpath (s-trim (with-current-buffer outbuf (buffer-string))))
                                   (lisp-path (s-concat outpath "/bin/sbcl")))
-                             (message "Acquired Lisp for <depot>.%s at %s" attribute lisp-path)
+                             (message "Acquired Lisp for <briefcase>.%s at %s" attribute lisp-path)
                              (sly lisp-path)))
                           (_ (with-current-buffer errbuf
                                (error "Failed to build '%s':\n%s" attribute (buffer-string)))))