fix: dialog draw-border arg, markdown/slot nil guards, +integration test suite

src/components/markdown.lisp

@@ -31,6 +31,7 @@
 ;; ─── Block-level parser ───────────────────────────────────────────────────────
 
 (defun split-string-into-lines (string)
+  (unless string (return-from split-string-into-lines (coerce nil 'vector)))
   (let ((result nil) (start 0))
     (flet ((add-line (end) (push (subseq string start end) result)))
       (loop for i from 0 below (length string)
@@ -212,6 +213,7 @@
               i))))
 
 (defun parse-blocks (text)
+  (unless text (return-from parse-blocks nil))
   (let ((lines (split-string-into-lines text)) (nodes nil) (i 0))
     (loop while (< i (length lines))
           do (let* ((line (string-trim (list #\return) (aref lines i)))
@@ -502,6 +504,7 @@
     (nreverse tokens)))
 
 (defun highlight-code (code language)
+  (unless code (return-from highlight-code nil))
   (let ((highlighter (get-highlighter (and language (string-downcase language)))))
     (unless highlighter (return-from highlight-code (list (cons code :plain))))
     (let ((tokens nil))
@@ -672,6 +675,7 @@
     lines))
 
 (defun render-markdown (text)
+  (unless text (return-from render-markdown ""))
   (let ((nodes (parse-blocks text)) (parts nil))
     (dolist (line (render-md nodes)) (push line parts))
     (with-output-to-string (s)