content: tree-wide revision diff (772/772)

content/diff + diff-versions enumerated ids top-level only (doc-ids/
doc-find), so diffs of documents with sections missed every nested add/
remove/change. Now via doc-tree-ids + doc-deep-find; sections excluded from
:changed (no own content), still reported in :added/:removed. Flat-doc
diffs unchanged. +9 store tests.

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

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))