content: document composition (compose.sx) + 17 tests (502/502)

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

lib/content/compose.sx

@@ -0,0 +1,42 @@
+;; content-on-sx — document composition.
+;;
+;; Combine documents (header + body + footer, templates, partials) into a new
+;; document. The result keeps the FIRST document's id and metadata; blocks are
+;; concatenated. Immutable — inputs are untouched. Block-id collisions across
+;; combined docs are the caller's concern (content/validate flags duplicates).
+;;
+;; Requires (loaded by harness): doc.sx.
+
+(define
+  content/concat
+  (fn (a b) (doc-with-blocks a (append (doc-blocks a) (doc-blocks b)))))
+
+(define
+  content/prepend
+  (fn (a b) (doc-with-blocks a (append (doc-blocks b) (doc-blocks a)))))
+
+(define
+  content/-concat-fold
+  (fn
+    (acc more)
+    (if
+      (= (len more) 0)
+      acc
+      (content/-concat-fold (content/concat acc (first more)) (rest more)))))
+
+(define
+  content/concat-all
+  (fn
+    (docs)
+    (if
+      (= (len docs) 0)
+      (doc-empty "merged")
+      (content/-concat-fold (first docs) (rest docs)))))
+
+;; wrap a document's blocks inside a single section (collapse to a subtree).
+;; Requires section.sx (mk-section) when used.
+(define
+  content/wrap-section
+  (fn
+    (doc section-id)
+    (doc-with-blocks doc (list (mk-section section-id (doc-blocks doc))))))

lib/content/conformance.sh

@@ -15,7 +15,7 @@ if [ ! -x "$SX_SERVER" ]; then
   fi
 fi
 
-SUITES=(block doc render api meta page page-full markdown text section stats table validate store snapshot crdt crdt-store sync md-import md-doc fed)
+SUITES=(block doc render api meta page page-full markdown text section compose stats table validate store snapshot crdt crdt-store sync md-import md-doc fed)
 
 OUT_JSON="lib/content/scoreboard.json"
 OUT_MD="lib/content/scoreboard.md"
@@ -45,6 +45,7 @@ run_suite() {
 (load "lib/content/meta.sx")
 (load "lib/content/text.sx")
 (load "lib/content/section.sx")
+(load "lib/content/compose.sx")
 (load "lib/content/stats.sx")
 (load "lib/content/table.sx")
 (load "lib/content/page.sx")

lib/content/scoreboard.json

@@ -10,6 +10,7 @@
     "markdown": {"pass": 20, "fail": 0},
     "text": {"pass": 20, "fail": 0},
     "section": {"pass": 25, "fail": 0},
+    "compose": {"pass": 17, "fail": 0},
     "stats": {"pass": 17, "fail": 0},
     "table": {"pass": 15, "fail": 0},
     "validate": {"pass": 23, "fail": 0},
@@ -22,7 +23,7 @@
     "md-doc": {"pass": 12, "fail": 0},
     "fed": {"pass": 20, "fail": 0}
   },
-  "total_pass": 485,
+  "total_pass": 502,
   "total_fail": 0,
-  "total": 485
+  "total": 502
 }

lib/content/scoreboard.md

@@ -14,6 +14,7 @@ _Generated by `lib/content/conformance.sh`_
 | markdown | 20 | 0 | 20 |
 | text | 20 | 0 | 20 |
 | section | 25 | 0 | 25 |
+| compose | 17 | 0 | 17 |
 | stats | 17 | 0 | 17 |
 | table | 15 | 0 | 15 |
 | validate | 23 | 0 | 23 |
@@ -25,4 +26,4 @@ _Generated by `lib/content/conformance.sh`_
 | md-import | 38 | 0 | 38 |
 | md-doc | 12 | 0 | 12 |
 | fed | 20 | 0 | 20 |
-| **Total** | **485** | **0** | **485** |
+| **Total** | **502** | **0** | **502** |

lib/content/tests/compose.sx

@@ -0,0 +1,76 @@
+;; Extension — document composition.
+
+(st-bootstrap-classes!)
+(content/bootstrap!)
+(content-bootstrap-section!)
+
+(define
+  a
+  (doc-with-title
+    (doc-append (doc-empty "a") (mk-heading "h" 1 "A"))
+    "Doc A"))
+(define
+  b
+  (doc-append
+    (doc-append (doc-empty "b") (mk-text "p" "B1"))
+    (mk-text "q" "B2")))
+
+;; ── concat ──
+(define ab (content/concat a b))
+(content-test "concat ids" (doc-ids ab) (list "h" "p" "q"))
+(content-test "concat keeps first id" (doc-id ab) "a")
+(content-test "concat keeps first title" (doc-title ab) "Doc A")
+(content-test "concat immutable a" (doc-ids a) (list "h"))
+(content-test "concat immutable b" (doc-ids b) (list "p" "q"))
+
+;; ── prepend ──
+(define ba (content/prepend a b))
+(content-test "prepend ids" (doc-ids ba) (list "p" "q" "h"))
+(content-test "prepend keeps a id" (doc-id ba) "a")
+
+;; ── concat with empty ──
+(content-test
+  "concat empty right"
+  (doc-ids (content/concat a (doc-empty "e")))
+  (list "h"))
+(content-test
+  "concat empty left"
+  (doc-ids (content/concat (doc-empty "e") b))
+  (list "p" "q"))
+
+;; ── concat-all ──
+(define c (doc-append (doc-empty "c") (mk-divider "d")))
+(content-test
+  "concat-all order"
+  (doc-ids (content/concat-all (list a b c)))
+  (list "h" "p" "q" "d"))
+(content-test
+  "concat-all keeps first id"
+  (doc-id (content/concat-all (list a b c)))
+  "a")
+(content-test
+  "concat-all single"
+  (doc-ids (content/concat-all (list a)))
+  (list "h"))
+(content-test
+  "concat-all empty"
+  (doc-ids (content/concat-all (list)))
+  (list))
+
+;; ── render of composed doc ──
+(content-test
+  "composed renders"
+  (asHTML (content/concat a b))
+  "<h1>A</h1><p>B1</p><p>B2</p>")
+
+;; ── wrap-section collapses blocks into a subtree ──
+(define w (content/wrap-section ab "sec"))
+(content-test "wrap top-level is one section" (doc-ids w) (list "sec"))
+(content-test
+  "wrap children preserved"
+  (doc-tree-ids w)
+  (list "sec" "h" "p" "q"))
+(content-test
+  "wrap renders nested"
+  (asHTML w)
+  "<section><h1>A</h1><p>B1</p><p>B2</p></section>")

plans/content-on-sx.md

@@ -19,7 +19,7 @@ injected adapter, not core.
 
 ## Status (rolling)
 
-`bash lib/content/conformance.sh` → **485/485** (Phases 1–4 COMPLETE + extensions: HTML/SX escaping, Markdown render + import/export incl. tables & frontmatter (full round-trip), CRDT replication, tree-aware validation, snapshot cache, doc metadata, plain-text render, nested block trees, doc stats, table block, HTML page wrapper + SEO page)
+`bash lib/content/conformance.sh` → **502/502** (Phases 1–4 COMPLETE + extensions: HTML/SX escaping, Markdown render + import/export incl. tables & frontmatter (full round-trip), CRDT replication, tree-aware validation, snapshot cache, doc metadata, plain-text render, nested block trees, doc stats, table block, HTML page wrapper + SEO page, doc composition)
 
 ## Ground rules
 
@@ -91,9 +91,15 @@ lib/content/api.sx ── (content/edit) (content/render) (content/history) ─
 - [x] table block (`table.sx`: CtTable, renders html/sx/text/md, validated)
 - [x] HTML page wrapper (`page.sx`: content/page, escaped title from metadata)
 - [x] SEO page (`page-full.sx`: content/page-full, lang + meta description from excerpt)
+- [x] document composition (`compose.sx`: concat/prepend/concat-all/wrap-section)
 
 ## Progress log
 
+- 2026-06-07 — Extension: document composition (`compose.sx`). `content/concat`
+  / `content/prepend` / `content/concat-all` combine documents (keeping the
+  first's id + metadata, concatenating blocks, immutable); `content/wrap-section`
+  collapses a doc's blocks into a single nested section. For assembling pages
+  from header/body/footer parts and templates. 17 tests; suite 502/502.
 - 2026-06-07 — Extension: SEO-complete page (`page-full.sx`). `content/page-full`
   extends content/page with `<html lang="en">` and a `<meta name="description">`
   drawn from the document excerpt (plain text, escaped, 160 chars), composing the