content: TOC rendering (toc.sx) + 8 tests (594/594)

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

lib/content/toc.sx

@@ -0,0 +1,68 @@
+;; content-on-sx — table-of-contents rendering.
+;;
+;; Turns content/headings into a user-facing TOC: a Markdown bullet list indented
+;; by heading level, and an HTML <ul> of anchor links (#id). The blog page links
+;; these to heading anchors.
+;;
+;; Requires (loaded by harness): query.sx (content/headings), render.sx
+;; (htmlEscaped).
+
+(define toc-nl (str "\n"))
+(define
+  toc-join
+  (fn
+    (sep parts)
+    (cond
+      ((= (len parts) 0) "")
+      ((= (len parts) 1) (first parts))
+      (else (str (first parts) sep (toc-join sep (rest parts)))))))
+
+(define
+  toc-indent
+  (fn
+    (n)
+    (if (<= n 0) "" (str "  " (toc-indent (- n 1))))))
+(define toc-esc (fn (s) (str (st-send s "htmlEscaped" (list)))))
+
+(define
+  content/toc-markdown
+  (fn
+    (doc)
+    (toc-join
+      toc-nl
+      (map
+        (fn
+          (h)
+          (str
+            (toc-indent (- (get h :level) 1))
+            "- ["
+            (get h :text)
+            "](#"
+            (get h :id)
+            ")"))
+        (content/headings doc)))))
+
+(define
+  content/toc-html
+  (fn
+    (doc)
+    (let
+      ((hs (content/headings doc)))
+      (if
+        (= (len hs) 0)
+        ""
+        (str
+          "<ul>"
+          (toc-join
+            ""
+            (map
+              (fn
+                (h)
+                (str
+                  "<li><a href=\"#"
+                  (get h :id)
+                  "\">"
+                  (toc-esc (get h :text))
+                  "</a></li>"))
+              hs))
+          "</ul>")))))