content: deep tree editing (tree-edit.sx) + 17 tests (551/551)

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

lib/content/tree-edit.sx

@@ -0,0 +1,96 @@
+;; content-on-sx — deep tree editing.
+;;
+;; Mutate blocks anywhere in the nested tree (descending into CtSection children),
+;; complementing the top-level doc ops and the deep-find read path. All return
+;; new documents (immutable).
+;;
+;; Requires (loaded by harness): doc.sx, section.sx (section? / section-children /
+;; section-with-children / section-append).
+
+;; map f over every block in the tree, replacing the one whose id matches.
+(define
+  block-tree-update
+  (fn
+    (blocks id f)
+    (map
+      (fn
+        (b)
+        (if
+          (= (blk-id b) id)
+          (f b)
+          (if
+            (section? b)
+            (section-with-children
+              b
+              (block-tree-update (section-children b) id f))
+            b)))
+      blocks)))
+
+;; remove the block with id from anywhere in the tree.
+(define
+  block-tree-delete
+  (fn
+    (blocks id)
+    (map
+      (fn
+        (b)
+        (if
+          (section? b)
+          (section-with-children
+            b
+            (block-tree-delete (section-children b) id))
+          b))
+      (filter (fn (b) (if (= (blk-id b) id) false true)) blocks))))
+
+;; append a block into the children of the section with section-id.
+(define
+  block-tree-insert-into
+  (fn
+    (blocks section-id block)
+    (map
+      (fn
+        (b)
+        (if
+          (section? b)
+          (if
+            (= (blk-id b) section-id)
+            (section-append b block)
+            (section-with-children
+              b
+              (block-tree-insert-into (section-children b) section-id block)))
+          b))
+      blocks)))
+
+;; ── document-level deep ops ──
+(define
+  doc-deep-update
+  (fn
+    (doc id field value)
+    (doc-with-blocks
+      doc
+      (block-tree-update
+        (doc-blocks doc)
+        id
+        (fn (b) (blk-set b field value))))))
+
+(define
+  doc-deep-replace
+  (fn
+    (doc id newblock)
+    (doc-with-blocks
+      doc
+      (block-tree-update (doc-blocks doc) id (fn (b) newblock)))))
+
+(define
+  doc-deep-delete
+  (fn
+    (doc id)
+    (doc-with-blocks doc (block-tree-delete (doc-blocks doc) id))))
+
+(define
+  doc-deep-insert-into
+  (fn
+    (doc section-id block)
+    (doc-with-blocks
+      doc
+      (block-tree-insert-into (doc-blocks doc) section-id block))))