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/validate.sx

@@ -1,9 +1,10 @@
 ;; content-on-sx — document integrity validation.
 ;;
-;; Guards imports, edits and federated input: checks each block's id and the
-;; required fields/types for its kind, plus document-level duplicate ids. Returns
-;; a list of issue dicts {:id :kind :detail}; an empty list means valid. Dispatch
-;; on block type is a validation-boundary concern, not core behaviour.
+;; Guards imports, edits and federated input: walks the whole block TREE (into
+;; nested sections) checking each block's id and required fields/types, plus
+;; tree-wide duplicate ids. Returns issue dicts {:id :kind :detail}; empty = ok.
+;; Tree detection is inline (class + st-iv-get) so this file needs no section.sx.
+;; Dispatch on block type is a validation-boundary concern, not core behaviour.
 ;;
 ;; Requires (loaded by harness): block.sx, doc.sx.
 
@@ -35,6 +36,30 @@
 
 (define ct-uniq (fn (xs) (ct-uniq-loop xs (list))))
 
+;; ── tree flatten (descends into CtSection children; guards malformed children) ──
+(define
+  ct-section-block?
+  (fn (b) (and (st-instance? b) (= (get b :class) "CtSection"))))
+(define
+  ct-tree-blocks
+  (fn
+    (blocks)
+    (if
+      (= (len blocks) 0)
+      (list)
+      (let
+        ((b (first blocks)))
+        (append
+          (cons
+            b
+            (if
+              (ct-section-block? b)
+              (let
+                ((ch (st-iv-get b "children")))
+                (if (list? ch) (ct-tree-blocks ch) (list)))
+              (list)))
+          (ct-tree-blocks (rest blocks)))))))
+
 ;; ── id checks ──
 (define
   content/-id-issues
@@ -120,32 +145,36 @@
               id
               (list? (blk-get b "items"))
               "list items must be a list")))
+        ((= t "section")
+          (ct-field-issue
+            id
+            (list? (blk-get b "children"))
+            "section children must be a list"))
         (else (list (ct-issue id "type" (str "unknown block type: " t))))))))
 
 (define
   content/-block-issues
   (fn (b) (append (content/-id-issues b) (content/-field-issues b))))
 
-;; ── document-level: duplicate ids ──
+;; ── duplicate ids across the whole tree ──
 (define
   content/-dup-issues
   (fn
-    (doc)
-    (let
-      ((ids (doc-ids doc)))
-      (map
-        (fn (id) (ct-issue id "duplicate" (str "duplicate block id: " id)))
-        (ct-uniq
-          (filter (fn (id) (> (ct-count-in id ids) 1)) ids))))))
+    (ids)
+    (map
+      (fn (id) (ct-issue id "duplicate" (str "duplicate block id: " id)))
+      (ct-uniq (filter (fn (id) (> (ct-count-in id ids) 1)) ids)))))
 
 ;; ── public ──
 (define
   content/validate
   (fn
     (doc)
-    (append
-      (content/-dup-issues doc)
-      (ct-flatmap content/-block-issues (doc-blocks doc)))))
+    (let
+      ((all (ct-tree-blocks (doc-blocks doc))))
+      (append
+        (content/-dup-issues (map (fn (b) (blk-id b)) all))
+        (ct-flatmap content/-block-issues all)))))
 
 (define
   content/valid?