content: Markdown frontmatter -> metadata + 9 tests (469/469)

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

lib/content/tests/md-import.sx

@@ -1,5 +1,5 @@
 ;; Extension — Markdown import adapter (markdown text -> blocks), inverse of
-;; asMarkdown. Round-trips canonical Markdown.
+;; asMarkdown. Round-trips canonical Markdown; parses frontmatter + tables.
 
 (st-bootstrap-classes!)
 (content/bootstrap!)
@@ -130,6 +130,43 @@
   (doc-types dmix)
   (list "heading" "table" "text"))
 
+;; ── frontmatter ──
+(define
+  dfm
+  (md/import
+    (str
+      "---"
+      nl
+      "title: My Post"
+      nl
+      "slug: my-post"
+      nl
+      "tags: a, b, c"
+      nl
+      "---"
+      nl
+      "# Hi"
+      nl
+      nl
+      "body")
+    "d"))
+(content-test "fm title" (doc-title dfm) "My Post")
+(content-test "fm slug" (doc-slug dfm) "my-post")
+(content-test "fm tags" (doc-tags dfm) (list "a" "b" "c"))
+(content-test "fm body types" (doc-types dfm) (list "heading" "text"))
+(content-test
+  "fm body content"
+  (str (blk-send (doc-find dfm "b0") "text"))
+  "Hi")
+(content-test "no fm title nil" (doc-title (md/import "# Hi" "d")) nil)
+(content-test
+  "hr not frontmatter"
+  (doc-types (md/import (str "text" nl nl "---") "d"))
+  (list "text" "divider"))
+(define dfmo (md/import (str "---" nl "title: T" nl "---") "d"))
+(content-test "fm only title" (doc-title dfmo) "T")
+(content-test "fm only empty body" (doc-ids dfmo) (list))
+
 ;; ── round-trip: import . export == identity (canonical markdown) ──
 (define
   src