I'm dumb. Read-sequence destructively modifies the sequence rather than handing it back.

src/posts.lisp

@@ -55,8 +55,9 @@
          (parse-field (str)
            (nth-value 1 (cl-ppcre:scan-to-strings "[a-zA-Z]+: (.*)" str)))
          (slurp-remainder ()
-           (read-sequence (make-string (- (file-length in) (file-position in)))
-                          in :start (file-position in))))
+           (let ((seq (make-string (- (file-length in) (file-position in)))))
+             (read-sequence seq in)
+             (remove #\Nul seq))))
     (check-header)
     (let ((args (loop for field in '("title" "tags" "date" "format")
                    for line = (read-line in nil)