diff --git a/lib/content/crdt-tree.sx b/lib/content/crdt-tree.sx
index 9ba58d49..9b76f42a 100644
--- a/lib/content/crdt-tree.sx
+++ b/lib/content/crdt-tree.sx
@@ -4,13 +4,14 @@
 ;; (the id of its containing section, "" = root) alongside its Logoot position.
 ;; Merge is still a join — it reuses crdt.sx's position/register/field merges and
 ;; adds parent (immutable, set once at insert). Materialisation rebuilds the
-;; ordered tree: root = elements with parent "", a section's children = elements
-;; whose parent is that section's id, each sorted by position. Commutative,
-;; associative, idempotent like the flat layer; concurrent inserts into the same
-;; or different parents converge deterministically.
+;; ordered tree: root = elements with parent "" (plus ORPHANS — elements whose
+;; parent is not a live section, e.g. after a concurrent delete-section +
+;; insert-child, so content is never silently lost); a section's children =
+;; elements whose parent is that section's id. Commutative/associative/idempotent
+;; like the flat layer.
 ;;
 ;; Requires (loaded by harness): crdt.sx (merge helpers + live/sort/materialise
-;; bits), block.sx, doc.sx, section.sx (mk-section).
+;; bits + crdt-member?), block.sx, doc.sx, section.sx (mk-section).
 
 (define ctt-merge-parent (fn (p1 p2) (if (= p1 nil) p2 p1)))
 
@@ -129,6 +130,34 @@
       (crdt-tree-apply-all (crdt-tree-apply state (first ops)) (rest ops)))))
 
 ;; ── materialise to a Phase-1 document (rebuild the ordered tree) ──
+(define
+  ctt-live-section-ids
+  (fn
+    (state)
+    (map
+      (fn (e) (get e :id))
+      (filter
+        (fn (e) (= (get e :type) "section"))
+        (crdt-live-elements state)))))
+
+;; an element belongs at root if its parent is "" or its parent is not a live
+;; section (orphan-reparenting: don't lose content when its section is deleted).
+(define
+  ctt-roots
+  (fn
+    (state)
+    (let
+      ((secids (ctt-live-section-ids state)))
+      (crdt-sort-by-pos
+        (filter
+          (fn
+            (e)
+            (if
+              (= (get e :parent) "")
+              true
+              (if (crdt-member? (get e :parent) secids) false true)))
+          (crdt-live-elements state))))))
+
 (define
   ctt-children
   (fn
@@ -157,8 +186,8 @@
     (doc-id state)
     (doc-new
       doc-id
-      (map (fn (e) (ctt-element->block state e)) (ctt-children state "")))))
+      (map (fn (e) (ctt-element->block state e)) (ctt-roots state)))))
 
 (define
   crdt-tree-order
-  (fn (state) (map (fn (e) (get e :id)) (ctt-children state ""))))
+  (fn (state) (map (fn (e) (get e :id)) (ctt-roots state))))
diff --git a/lib/content/scoreboard.json b/lib/content/scoreboard.json
index b8c4625b..526cba50 100644
--- a/lib/content/scoreboard.json
+++ b/lib/content/scoreboard.json
@@ -34,7 +34,7 @@
     "store": {"pass": 29, "fail": 0},
     "snapshot": {"pass": 20, "fail": 0},
     "crdt": {"pass": 34, "fail": 0},
-    "crdt-tree": {"pass": 17, "fail": 0},
+    "crdt-tree": {"pass": 21, "fail": 0},
     "crdt-blocks": {"pass": 7, "fail": 0},
     "crdt-store": {"pass": 14, "fail": 0},
     "sync": {"pass": 14, "fail": 0},
@@ -42,7 +42,7 @@
     "md-doc": {"pass": 12, "fail": 0},
     "fed": {"pass": 20, "fail": 0}
   },
-  "total_pass": 738,
+  "total_pass": 742,
   "total_fail": 0,
-  "total": 738
+  "total": 742
 }
diff --git a/lib/content/scoreboard.md b/lib/content/scoreboard.md
index 9cdf12c2..0811d718 100644
--- a/lib/content/scoreboard.md
+++ b/lib/content/scoreboard.md
@@ -38,11 +38,11 @@ _Generated by `lib/content/conformance.sh`_
 | store | 29 | 0 | 29 |
 | snapshot | 20 | 0 | 20 |
 | crdt | 34 | 0 | 34 |
-| crdt-tree | 17 | 0 | 17 |
+| crdt-tree | 21 | 0 | 21 |
 | crdt-blocks | 7 | 0 | 7 |
 | crdt-store | 14 | 0 | 14 |
 | sync | 14 | 0 | 14 |
 | md-import | 38 | 0 | 38 |
 | md-doc | 12 | 0 | 12 |
 | fed | 20 | 0 | 20 |
-| **Total** | **738** | **0** | **738** |
+| **Total** | **742** | **0** | **742** |
diff --git a/lib/content/tests/crdt-tree.sx b/lib/content/tests/crdt-tree.sx
index b70c6f95..677a3593 100644
--- a/lib/content/tests/crdt-tree.sx
+++ b/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>")
diff --git a/plans/content-on-sx.md b/plans/content-on-sx.md
index 69d5cb74..f4c920c9 100644
--- a/plans/content-on-sx.md
+++ b/plans/content-on-sx.md
@@ -19,7 +19,7 @@ injected adapter, not core.
 
 ## Status (rolling)
 
-`bash lib/content/conformance.sh` → **738/738** (Phases 1–4 COMPLETE + ~34 extensions, hardened: HTML/SX escaping, Markdown render + import/export incl. tables & frontmatter (full round-trip), CvRDT flat + nested-tree + durable replication, tree-aware validation, snapshot cache, doc metadata, plain-text render, nested block trees + deep editing + flatten + relative reorder, doc stats + summary + multi-doc index, table + callout + media blocks, HTML page wrapper + SEO page, doc composition + id-remap, portable data + wire serialization, block query + transforms + find/replace, TOC + anchored headings + outline, normalization)
+`bash lib/content/conformance.sh` → **742/742** (Phases 1–4 COMPLETE + ~34 extensions, hardened: HTML/SX escaping, Markdown render + import/export incl. tables & frontmatter (full round-trip), CvRDT flat + nested-tree + durable replication, tree-aware validation, snapshot cache, doc metadata, plain-text render, nested block trees + deep editing + flatten + relative reorder, doc stats + summary + multi-doc index, table + callout + media blocks, HTML page wrapper + SEO page, doc composition + id-remap, portable data + wire serialization, block query + transforms + find/replace, TOC + anchored headings + outline, normalization)
 
 ## Ground rules
 
@@ -113,6 +113,13 @@ lib/content/api.sx ── (content/edit) (content/render) (content/history) ─
 
 ## Progress log
 
+- 2026-06-07 — Hardening: tree-CRDT orphan reparenting. Concurrent
+  delete-section + insert-child previously orphaned the child (its parent no
+  longer a live section) → silently dropped from materialise. Fixed
+  `crdt-tree-materialize`/`crdt-tree-order` to root any element whose parent is
+  "" OR not a live section, so content is never lost on concurrent edits. +4
+  tests (orphan survives, commutes, content preserved, renders at root). Suite
+  742/742.
 - 2026-06-07 — Hardening: regression suite `crdt-blocks` (7 tests) locking that
   non-core block types (callout/table/media/section) survive both the flat and
   nested-tree CvRDT materialise paths (insert → merge → materialise → render),