diff --git a/lib/content/conformance.sh b/lib/content/conformance.sh
index 52eae428..762ec963 100755
--- a/lib/content/conformance.sh
+++ b/lib/content/conformance.sh
@@ -15,7 +15,7 @@ if [ ! -x "$SX_SERVER" ]; then
   fi
 fi
 
-SUITES=(block doc render api meta page page-full markdown text section compose tree-edit move clone query toc anchor outline flatten transform normalize find-replace stats summary index table callout media data wire validate store snapshot crdt crdt-tree crdt-store sync md-import md-doc fed)
+SUITES=(block doc render api meta page page-full markdown text section compose tree-edit move clone query toc anchor outline flatten transform normalize find-replace stats summary index table callout media data wire validate store snapshot crdt crdt-tree crdt-blocks crdt-store sync md-import md-doc fed)
 
 OUT_JSON="lib/content/scoreboard.json"
 OUT_MD="lib/content/scoreboard.md"
diff --git a/lib/content/scoreboard.json b/lib/content/scoreboard.json
index bd3c1bc1..b8c4625b 100644
--- a/lib/content/scoreboard.json
+++ b/lib/content/scoreboard.json
@@ -35,13 +35,14 @@
     "snapshot": {"pass": 20, "fail": 0},
     "crdt": {"pass": 34, "fail": 0},
     "crdt-tree": {"pass": 17, "fail": 0},
+    "crdt-blocks": {"pass": 7, "fail": 0},
     "crdt-store": {"pass": 14, "fail": 0},
     "sync": {"pass": 14, "fail": 0},
     "md-import": {"pass": 38, "fail": 0},
     "md-doc": {"pass": 12, "fail": 0},
     "fed": {"pass": 20, "fail": 0}
   },
-  "total_pass": 731,
+  "total_pass": 738,
   "total_fail": 0,
-  "total": 731
+  "total": 738
 }
diff --git a/lib/content/scoreboard.md b/lib/content/scoreboard.md
index 65aeabd4..9cdf12c2 100644
--- a/lib/content/scoreboard.md
+++ b/lib/content/scoreboard.md
@@ -39,9 +39,10 @@ _Generated by `lib/content/conformance.sh`_
 | snapshot | 20 | 0 | 20 |
 | crdt | 34 | 0 | 34 |
 | crdt-tree | 17 | 0 | 17 |
+| 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** | **731** | **0** | **731** |
+| **Total** | **738** | **0** | **738** |
diff --git a/lib/content/tests/crdt-blocks.sx b/lib/content/tests/crdt-blocks.sx
new file mode 100644
index 00000000..7d4619ad
--- /dev/null
+++ b/lib/content/tests/crdt-blocks.sx
@@ -0,0 +1,136 @@
+;; Hardening — non-core block types (callout/table/media/section) survive the
+;; flat and tree CvRDT materialise paths (regression for the ct-class-for-type
+;; fix: these route through crdt-element->block -> mk-block).
+
+(st-bootstrap-classes!)
+(content-bootstrap-blocks!)
+(content-bootstrap-doc!)
+(content-bootstrap-render!)
+(content-bootstrap-section!)
+(content-bootstrap-callout!)
+(content-bootstrap-table!)
+(content-bootstrap-media!)
+
+;; ── flat CRDT: callout / table / media leaves ──
+(define
+  s
+  (crdt-apply-all
+    (crdt-empty)
+    (list
+      (crdt-op-insert
+        "co"
+        "callout"
+        (crdt-pos 1 0)
+        (list (list "kind" "note") (list "text" "hi"))
+        1
+        0)
+      (crdt-op-insert
+        "tb"
+        "table"
+        (crdt-pos 2 0)
+        (list (list "headers" (list "A")) (list "rows" (list (list "1"))))
+        1
+        0)
+      (crdt-op-insert
+        "vid"
+        "media"
+        (crdt-pos 3 0)
+        (list (list "kind" "video") (list "src" "/v.mp4"))
+        1
+        0))))
+(content-test
+  "flat crdt callout render"
+  (asHTML (crdt-materialize "d" s))
+  "<aside class=\"callout callout-note\">hi</aside><table><thead><tr><th>A</th></tr></thead><tbody><tr><td>1</td></tr></tbody></table><video src=\"/v.mp4\" controls></video>")
+(content-test "flat crdt order" (crdt-order s) (list "co" "tb" "vid"))
+
+;; ── flat CRDT: callout field via LWW update ──
+(define s2 (crdt-update s "co" "text" "edited" 5 1))
+(content-test
+  "flat crdt callout update"
+  (str (blk-send (doc-find (crdt-materialize "d" s2) "co") "text"))
+  "edited")
+
+;; ── tree CRDT: callout/table inside a section ──
+(define
+  t
+  (crdt-tree-apply-all
+    (crdt-empty)
+    (list
+      (crdt-tree-op-insert
+        "sec"
+        "section"
+        (crdt-pos 1 0)
+        ""
+        (list)
+        1
+        0)
+      (crdt-tree-op-insert
+        "co"
+        "callout"
+        (crdt-pos 1 0)
+        "sec"
+        (list (list "kind" "tip") (list "text" "T"))
+        1
+        0)
+      (crdt-tree-op-insert
+        "tb"
+        "table"
+        (crdt-pos 2 0)
+        "sec"
+        (list (list "headers" (list "H")) (list "rows" (list)))
+        1
+        0))))
+(content-test
+  "tree crdt nested blocks"
+  (doc-tree-ids (crdt-tree-materialize "d" t))
+  (list "sec" "co" "tb"))
+(content-test
+  "tree crdt nested render"
+  (asHTML (crdt-tree-materialize "d" t))
+  "<section><aside class=\"callout callout-tip\">T</aside><table><thead><tr><th>H</th></tr></thead><tbody></tbody></table></section>")
+
+;; ── tree CRDT: concurrent callout inserts into a section converge ──
+(define
+  base
+  (crdt-tree-insert
+    (crdt-empty)
+    "sec"
+    "section"
+    (crdt-pos 1 0)
+    ""
+    (list)
+    1
+    0))
+(define
+  rA
+  (crdt-tree-insert
+    base
+    "x"
+    "callout"
+    (crdt-pos 5 1)
+    "sec"
+    (list (list "kind" "note") (list "text" "A"))
+    2
+    1))
+(define
+  rB
+  (crdt-tree-insert
+    base
+    "y"
+    "media"
+    (crdt-pos 5 2)
+    "sec"
+    (list (list "kind" "audio") (list "src" "/a.mp3"))
+    2
+    2))
+(content-test
+  "tree crdt mixed converge"
+  (=
+    (get (crdt-tree-merge rA rB) :elements)
+    (get (crdt-tree-merge rB rA) :elements))
+  true)
+(content-test
+  "tree crdt mixed ids"
+  (doc-tree-ids (crdt-tree-materialize "d" (crdt-tree-merge rA rB)))
+  (list "sec" "x" "y"))
diff --git a/plans/content-on-sx.md b/plans/content-on-sx.md
index d30126bc..69d5cb74 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` → **731/731** (Phases 1–4 COMPLETE + ~34 extensions: 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` → **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)
 
 ## Ground rules
 
@@ -113,6 +113,12 @@ lib/content/api.sx ── (content/edit) (content/render) (content/history) ─
 
 ## Progress log
 
+- 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),
+  the integration the ct-class-for-type fix repaired. Verified flat + tree,
+  including concurrent mixed-type inserts into a section converging. Suite
+  738/738.
 - 2026-06-07 — Hardening: fixed `ct-class-for-type` (block.sx) to map all block
   tags (added section/table/callout/media). Latent bug: `content/from-data` and
   CRDT materialise of callout/media blocks failed with "unknown block type" (they