content: plain-text render + excerpt (text.sx) + 20 tests (385/385)

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` → **365/365** (Phases 1–4 COMPLETE + extensions: HTML/SX escaping, Markdown render+import, durable CRDT replication, validation, snapshot cache, doc metadata)
+`bash lib/content/conformance.sh` → **385/385** (Phases 1–4 COMPLETE + 9 extensions: HTML/SX escaping, Markdown render+import, CRDT replication, validation, snapshot cache, doc metadata, plain-text render)
 
 ## Ground rules
 
@@ -84,9 +84,16 @@ lib/content/api.sx ── (content/edit) (content/render) (content/history) ─
 - [x] Markdown import adapter (`md-import.sx`: text → blocks, round-trips export)
 - [x] snapshot cache over replay (`snapshot.sx`: cache-not-primary, transparent)
 - [x] document metadata (`meta.sx`: title/slug/tags + Ghost title plumbing)
+- [x] plain-text render + excerpt (`text.sx`: asText, content/excerpt)
 
 ## Progress log
 
+- 2026-06-07 — Extension: plain-text render + excerpts (`text.sx`). Fourth
+  boundary format via polymorphic `asText` (heading/text/code/quote→text,
+  image→alt, embed/divider→"", list→", "-joined); the document joins non-empty
+  child texts with a space. `content/render doc "text"`, `content/text`,
+  `content/excerpt doc n` (first n chars + "…" if truncated). For previews,
+  meta-descriptions, search indexing. 20 tests; suite 385/385.
 - 2026-06-07 — Extension: document metadata (`meta.sx`). CtDoc gained optional
   title/slug/tags ivars (declared in doc.sx, default nil/empty, no effect on
   block ops). Reads via message dispatch; copy-on-write setters