content: document normalization (normalize.sx) + 11 tests (605/605)

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

lib/content/normalize.sx

@@ -0,0 +1,49 @@
+;; content-on-sx — document normalization.
+;;
+;; A cleanup pass: drop empty text blocks and empty sections across the tree.
+;; Sections are normalised first, so a section that becomes empty (all children
+;; dropped) is itself dropped. For tidying imported/edited documents. Immutable.
+;; Inline tree handling (no section.sx dep).
+;;
+;; Requires (loaded by harness): block.sx, doc.sx.
+
+(define
+  norm-section?
+  (fn (b) (and (st-instance? b) (= (get b :class) "CtSection"))))
+(define
+  norm-empty-text?
+  (fn (b) (and (= (blk-type b) "text") (= (str (blk-get b "text")) ""))))
+(define
+  norm-empty-section?
+  (fn
+    (b)
+    (and
+      (norm-section? b)
+      (let
+        ((ch (st-iv-get b "children")))
+        (or (= ch nil) (= (len ch) 0))))))
+
+(define
+  norm-recurse
+  (fn
+    (b)
+    (if
+      (norm-section? b)
+      (let
+        ((ch (st-iv-get b "children")))
+        (if (list? ch) (st-iv-set! b "children" (norm-blocks ch)) b))
+      b)))
+
+(define
+  norm-keep?
+  (fn
+    (b)
+    (if (norm-empty-text? b) false (if (norm-empty-section? b) false true))))
+
+(define
+  norm-blocks
+  (fn (blocks) (filter norm-keep? (map norm-recurse blocks))))
+
+(define
+  content/normalize
+  (fn (doc) (doc-with-blocks doc (norm-blocks (doc-blocks doc)))))