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

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

plans/content-on-sx.md

@@ -19,7 +19,7 @@ injected adapter, not core.
 
 ## Status (rolling)
 
-`bash lib/content/conformance.sh` → **238/238** (Phases 1–4 COMPLETE + extensions: HTML escaping)
+`bash lib/content/conformance.sh` → **243/243** (Phases 1–4 COMPLETE + extensions: HTML + SX escaping)
 
 ## Ground rules
 
@@ -77,10 +77,15 @@ lib/content/api.sx ── (content/edit) (content/render) (content/history) ─
 
 ## Extensions (post-roadmap)
 - [x] HTML escaping at the render boundary (`String>>htmlEscaped`: & < > ")
-- [ ] asSx wire string-escaping (" and \ in SX string literals)
+- [x] asSx wire string-escaping (`String>>sxEscaped`: \ and " in SX literals)
 
 ## Progress log
 
+- 2026-06-07 — Extension: asSx wire string-escaping. Added `String>>sxEscaped`
+  (escapes `\`→`\\` then `"`→`\"`) and routed every `asSx` text/attr/list-item
+  through it, so the SX wire format stays valid when content contains quotes or
+  backslashes. +5 render tests (expected strings built from `q`/`bs` helpers to
+  avoid escaping miscounts). Suite 243/243.
 - 2026-06-07 — Extension: HTML escaping at the render boundary. Added
   `String>>htmlEscaped` (recursive char walk escaping & < > ", order-safe so &
   isn't double-escaped) and routed every `asHTML` text/attr through it — heading,