content: Markdown render mode (asMarkdown) + 20 tests (263/263)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/content/api.sx

@@ -49,7 +49,8 @@
     (if (content/op? ops) (doc-apply doc ops) (doc-apply-all doc ops))))
 
 ;; ── render boundary ──
-;; fmt is "html"/"sx" (or :html/:sx — keywords evaluate to their name).
+;; fmt is "html"/"sx"/"md" (or :html/:sx/:md — keywords evaluate to their name).
+;; "md" needs markdown.sx loaded.
 (define
   content/render
   (fn
@@ -57,6 +58,8 @@
     (cond
       ((= fmt "html") (asHTML doc))
       ((= fmt "sx") (asSx doc))
+      ((= fmt "md") (asMarkdown doc))
+      ((= fmt "markdown") (asMarkdown doc))
       (else (error (str "unknown render format: " fmt))))))
 
 (define content/html asHTML)