diff --git a/lib/content/scoreboard.json b/lib/content/scoreboard.json
index 30edd305..34cca8ab 100644
--- a/lib/content/scoreboard.json
+++ b/lib/content/scoreboard.json
@@ -31,7 +31,7 @@
     "data": {"pass": 25, "fail": 0},
     "wire": {"pass": 11, "fail": 0},
     "validate": {"pass": 23, "fail": 0},
-    "store": {"pass": 37, "fail": 0},
+    "store": {"pass": 46, "fail": 0},
     "snapshot": {"pass": 20, "fail": 0},
     "crdt": {"pass": 34, "fail": 0},
     "crdt-tree": {"pass": 21, "fail": 0},
@@ -42,7 +42,7 @@
     "md-doc": {"pass": 12, "fail": 0},
     "fed": {"pass": 20, "fail": 0}
   },
-  "total_pass": 763,
+  "total_pass": 772,
   "total_fail": 0,
-  "total": 763
+  "total": 772
 }
diff --git a/lib/content/scoreboard.md b/lib/content/scoreboard.md
index 5ce5087f..b3e0a611 100644
--- a/lib/content/scoreboard.md
+++ b/lib/content/scoreboard.md
@@ -35,7 +35,7 @@ _Generated by `lib/content/conformance.sh`_
 | data | 25 | 0 | 25 |
 | wire | 11 | 0 | 11 |
 | validate | 23 | 0 | 23 |
-| store | 37 | 0 | 37 |
+| store | 46 | 0 | 46 |
 | snapshot | 20 | 0 | 20 |
 | crdt | 34 | 0 | 34 |
 | crdt-tree | 21 | 0 | 21 |
@@ -45,4 +45,4 @@ _Generated by `lib/content/conformance.sh`_
 | md-import | 38 | 0 | 38 |
 | md-doc | 12 | 0 | 12 |
 | fed | 20 | 0 | 20 |
-| **Total** | **763** | **0** | **763** |
+| **Total** | **772** | **0** | **772** |
diff --git a/lib/content/store.sx b/lib/content/store.sx
index ef840c13..d59ddbb9 100644
--- a/lib/content/store.sx
+++ b/lib/content/store.sx
@@ -5,9 +5,10 @@
 ;; replay of its op stream up to a sequence number; the materialised doc is a
 ;; cache, never primary state.
 ;;
-;; Requires (loaded by the harness): block.sx, doc.sx, and persist
-;; (event/backend/log/kv/api). The persist backend `b` is opened by the caller
-;; via (persist/open) and injected — content knows nothing about which backend.
+;; Requires (loaded by the harness): block.sx, doc.sx, section.sx (doc-deep-find
+;; + doc-tree-ids, for the tree-wide diff), plus persist (event/backend/log/kv/
+;; api). The persist backend `b` is opened by the caller via (persist/open) and
+;; injected — content knows nothing about which backend.
 
 (define content/-stream (fn (doc-id) (str "content:" doc-id)))
 
@@ -69,11 +70,18 @@
   (fn (b doc-id) (map (fn (ev) {:type (persist/event-type ev) :at (persist/event-at ev) :seq (persist/event-seq ev)}) (content/log b doc-id))))
 
 ;; ── diff between two materialised document versions ──
-;; Returns {:added (ids) :removed (ids) :changed (ids)} where changed = ids
-;; present in both whose block content differs.
-(define
-  content/-missing?
-  (fn (doc id) (= (ct-index-of (doc-blocks doc) id) -1)))
+;; Tree-wide: ids are enumerated across the whole block tree (descending into
+;; sections), so nested-block adds/removes/changes are detected, not just
+;; top-level ones. Returns {:added :removed :changed} (lists of ids):
+;;   :added   — ids present (anywhere) in `new` but not in `old`
+;;   :removed — ids present (anywhere) in `old` but not in `new`
+;;   :changed — content blocks present in both whose block value differs
+;; Section containers never appear in :changed (they hold no own content — a
+;; child change surfaces as that child's own entry); a whole section appearing
+;; or disappearing shows up in :added / :removed by its id.
+(define content/-all-ids (fn (doc) (doc-tree-ids doc)))
+
+(define content/-missing? (fn (doc id) (= (doc-deep-find doc id) nil)))
 
 (define
   content/-changed
@@ -83,15 +91,16 @@
       (fn
         (id)
         (let
-          ((bo (doc-find old id)) (bn (doc-find new id)))
+          ((bo (doc-deep-find old id)) (bn (doc-deep-find new id)))
           (cond
             ((= bo nil) false)
             ((= bn nil) false)
+            ((= (blk-type bo) "section") false)
             ((= bo bn) false)
             (else true))))
-      (doc-ids old))))
+      (content/-all-ids old))))
 
-(define content/diff (fn (old new) {:changed (content/-changed old new) :removed (filter (fn (id) (content/-missing? new id)) (doc-ids old)) :added (filter (fn (id) (content/-missing? old id)) (doc-ids new))}))
+(define content/diff (fn (old new) {:changed (content/-changed old new) :removed (filter (fn (id) (content/-missing? new id)) (content/-all-ids old)) :added (filter (fn (id) (content/-missing? old id)) (content/-all-ids new))}))
 
 ;; convenience: diff two persisted versions by seq.
 (define
diff --git a/lib/content/tests/store.sx b/lib/content/tests/store.sx
index f452b66d..d8fb85cb 100644
--- a/lib/content/tests/store.sx
+++ b/lib/content/tests/store.sx
@@ -178,3 +178,31 @@
   "op-log nested delete via content/at seq2"
   (doc-tree-ids (content/at B4 "nest" 2))
   (list "sec" "n"))
+
+;; ── diff is TREE-WIDE: nested-block add/change/remove are detected, and
+;; section containers never appear in :changed (a top-level-only diff would miss
+;; "n" entirely and instead flag the section). ──
+(define dn01 (content/diff-versions B4 "nest" 0 1))
+(content-test
+  "diff nested added (section + child)"
+  (get dn01 :added)
+  (list "sec" "n"))
+(content-test "diff nested added removed empty" (get dn01 :removed) (list))
+(content-test "diff nested added changed empty" (get dn01 :changed) (list))
+
+(define dn12 (content/diff-versions B4 "nest" 1 2))
+(content-test
+  "diff nested changed child only"
+  (get dn12 :changed)
+  (list "n"))
+(content-test "diff nested changed no add" (get dn12 :added) (list))
+(content-test "diff nested changed no remove" (get dn12 :removed) (list))
+
+(define dn23 (content/diff-versions B4 "nest" 2 3))
+(content-test "diff nested removed child" (get dn23 :removed) (list "n"))
+(content-test "diff nested removed no change" (get dn23 :changed) (list))
+
+(content-test
+  "diff nested no-op"
+  (get (content/diff-versions B4 "nest" 1 1) :changed)
+  (list))
diff --git a/plans/content-on-sx.md b/plans/content-on-sx.md
index c36178d4..c1f8aaa1 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` → **763/763** (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` → **772/772** (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 +113,18 @@ lib/content/api.sx ── (content/edit) (content/render) (content/history) ─
 
 ## Progress log
 
+- 2026-06-07 — Hardening: `content/diff` (and `content/diff-versions`) are now
+  TREE-WIDE. They enumerated ids via `doc-ids`/`doc-find` (top-level only), so a
+  diff between two versions of a document containing sections silently missed
+  every nested-block add/remove/change — the same class of seam as the by-id
+  op-log bug. Now ids come from `doc-tree-ids` and lookups from `doc-deep-find`,
+  so nested changes surface precisely. Section containers are excluded from
+  `:changed` (they hold no own content; a child change reports as that child),
+  while whole-section add/remove still shows in `:added`/`:removed`. Flat-doc
+  diffs are unchanged (deep == top-level with no sections). +9 store tests
+  (nested add = section+child, nested change = child only, nested remove,
+  no-op). 772/772.
+
 - 2026-06-07 — Feature: in-document prose search. `content/search-text` (and
   `content/search-text-ids`) return every content block, tree-wide, whose
   `(asText b)` contains a term — so search spans text/heading/code/quote/callout