content: asSx wire string-escaping (String>>sxEscaped) + 5 tests (243/243)

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

lib/content/tests/render.sx

@@ -1,5 +1,5 @@
 ;; Phase 1 — render boundary. asHTML / asSx are polymorphic message sends on
-;; blocks and the document. HTML escaping happens at the boundary.
+;; blocks and the document. Escaping happens at the boundary.
 
 (st-bootstrap-classes!)
 (content-bootstrap-blocks!)
@@ -109,3 +109,27 @@
   "escape code body"
   (asHTML (mk-code "xc" "html" "<div> & </div>"))
   "<pre><code class=\"language-html\">&lt;div&gt; &amp; &lt;/div&gt;</code></pre>")
+
+;; ── asSx string-escaping (build expected via q/bs to avoid miscounts) ──
+(define q1 (str "\""))
+(define bs (str "\\"))
+(content-test
+  "asSx escapes quote"
+  (asSx (mk-text "qt" (str "say " q1 "hi" q1)))
+  (str "(p " q1 "say " bs q1 "hi" bs q1 q1 ")"))
+(content-test
+  "asSx escapes backslash"
+  (asSx (mk-text "qb" (str "a" bs "b")))
+  (str "(p " q1 "a" bs bs "b" q1 ")"))
+(content-test
+  "asSx plain unchanged"
+  (asSx (mk-text "pp" "plain"))
+  "(p \"plain\")")
+(content-test
+  "asSx escapes image attr"
+  (asSx (mk-image "im" (str "/a" q1) "x"))
+  (str "(img :src " q1 "/a" bs q1 q1 " :alt " q1 "x" q1 ")"))
+(content-test
+  "asSx escapes list item"
+  (asSx (mk-list "lq" false (list (str "i" q1) "j")))
+  (str "(ul (li " q1 "i" bs q1 q1 ")(li " q1 "j" q1 "))"))