perf(ui): scope cooldown heartbeat to visible items

docs/research/2026-07-25-slice-h-a2-cooldown-scope.md

@@ -0,0 +1,24 @@
+# Slice H-a2 — retained cooldown heartbeat scope
+
+Retail updates item cooldown children from
+`UIElement_UIItem::DoHeartbeat @ 0x004E1DF0`. Hidden retained subtrees do not
+receive that heartbeat.
+
+The shared acdream controller now keeps the same one-result-per-item heartbeat,
+but:
+
+- returns before reading the clock or visiting a slot when the authoritative
+  enchantment registry has no cooldown entries;
+- visits a mounted `UiItemList` only when the list and every ancestor are
+  visible;
+- clears the frame's step projection first, so a hidden-only item cannot retain
+  a stale ring;
+- recomputes the authoritative step on the first heartbeat after the panel
+  becomes visible;
+- retains existing future-slot and shared-cooldown-group behavior.
+
+Focused tests cover shared groups/future cells, hidden-parent suppression and
+reopen, and the zero-work empty-registry path.
+
+Release gate: 3,781 App tests passed / 3 skipped; 8,265 complete-solution
+tests passed / 5 skipped.