content: tree-aware validation (descends into sections) + 6 tests (416/416)

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

lib/content/tests/validate.sx

@@ -1,8 +1,10 @@
-;; Extension — document integrity validation.
+;; Extension — document integrity validation (tree-aware: descends into sections).
+;; (Conformance loads section.sx before this suite.)
 
 (st-bootstrap-classes!)
 (content-bootstrap-blocks!)
 (content-bootstrap-doc!)
+(content-bootstrap-section!)
 
 ;; ── a fully valid document ──
 (define
@@ -114,3 +116,51 @@
       (mk-heading "hh" 2 "H"))
     (mk-text "tt" "T")))
 (content-test "all well-formed types valid" (content/valid? allgood) true)
+
+;; ── tree-aware: descends into sections ──
+(define
+  nested
+  (doc-append
+    (doc-empty "d")
+    (mk-section
+      "s"
+      (list (mk-heading "nh" 1 "H") (mk-text "np" "ok")))))
+(content-test "valid nested section" (content/valid? nested) true)
+
+(define
+  nested-bad
+  (doc-append
+    (doc-empty "d")
+    (mk-section "s" (list (mk-heading "nh" "notnum" "H")))))
+(content-test
+  "nested bad field detected"
+  (content/issue-kinds nested-bad)
+  (list "field"))
+
+;; valid section block itself
+(content-test
+  "section valid"
+  (content/valid? (doc-append (doc-empty "d") (mk-section "s" (list))))
+  true)
+(content-test
+  "section bad children"
+  (content/issue-kinds
+    (doc-append
+      (doc-empty "d")
+      (st-iv-set! (mk-section "s" (list)) "children" "nope")))
+  (list "field"))
+
+;; duplicate id across a section boundary (top-level id == nested id)
+(define
+  dup-tree
+  (doc-append
+    (doc-append (doc-empty "d") (mk-text "x" "top"))
+    (mk-section "s" (list (mk-text "x" "nested")))))
+(content-test
+  "tree-wide duplicate detected"
+  (len
+    (filter
+      (fn (i) (= (get i :kind) "duplicate"))
+      (content/validate dup-tree)))
+  1)
+(content-test "tree dup not valid" (content/valid? dup-tree) false)