content: tree-CRDT orphan reparenting (no content loss on concurrent delete-section) + 4 tests (742/742)

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

lib/content/tests/crdt-tree.sx

@@ -251,3 +251,39 @@
   "two-replica tree ids"
   (doc-tree-ids (crdt-tree-materialize "d" (crdt-tree-merge repl1 repl2)))
   (list "s1" "p1" "s2" "p2"))
+
+;; ── orphan reparenting: concurrent delete-section + insert-child ──
+;; A deletes section s; B inserts a child into s. After merge, s is gone but the
+;; child must survive (reparented to root), not silently vanish.
+(define delA (crdt-tree-delete base "s"))
+(define
+  insB
+  (crdt-tree-insert
+    base
+    "c"
+    "text"
+    (crdt-pos 9 0)
+    "s"
+    (list (list "text" "kept"))
+    5
+    2))
+(define orphan-merge (crdt-tree-merge delA insB))
+(content-test
+  "orphan survives delete-section"
+  (doc-tree-ids (crdt-tree-materialize "d" orphan-merge))
+  (list "h" "c"))
+(content-test
+  "orphan reparent commutes"
+  (same? orphan-merge (crdt-tree-merge insB delA))
+  true)
+(content-test
+  "orphan content preserved"
+  (str
+    (blk-send
+      (doc-deep-find (crdt-tree-materialize "d" orphan-merge) "c")
+      "text"))
+  "kept")
+(content-test
+  "orphan render at root"
+  (asHTML (crdt-tree-materialize "d" orphan-merge))
+  "<h2>Sub</h2><p>kept</p>")