Editor: composition structure wireframe (read-only)

docs/architecture/10-interaction-and-feedback.md

@@ -221,6 +221,19 @@ below) like `PaneSplitHandle`, with the gesture in `useRowResizeDrag` (the row t
 _(Consulted via `/council` → WAI-ARIA APG `windowsplitter`. This bullet is the contract;
 cite it, not the APG file.)_
 
+**Resolved — composition structure wireframe.** The preview toolbar's structure disclosure (a
+read-only schematic of the spec's multi-view composition — `CompositionWireframe`, arch 08) is a
+**WAI-ARIA APG `tree`** inside a disclosure popover (`usePopover`): bare nested boxes are
+`tree` → `treeitem` → `group`, single-select via `aria-selected`, **one tab stop with a roving
+tabindex**, arrow keys in **logical (document) order** — Up/Down between nodes, Left → parent,
+Right → first child, Home/End, Enter/Space activate — not spatial, since a mixed horizontal/
+vertical layout makes spatial arrows ambiguous. Selecting a box reveals + selects that view's
+source range in the editor (`AppStore.requestRevealView`) but **does not steal focus**, so the
+wireframe stays the active surface while the editor scrolls to follow; the editor selection is the
+single source of truth. The toolbar glyph appears **only for a composed spec** — a single-view
+spec hides the affordance rather than disclosing an empty tree. _(Council: APG treeview; the
+cursor-scoping reachability rationale is in [arch 08](08-vega-editor-techniques.md).)_
+
 **Resolved — pane toggle strip.** The persistent show/hide strip (spec §01A) is a **WAI-ARIA
 APG `toolbar`** (`role="toolbar"`, `aria-orientation="vertical"`, an `aria-label` such as
 "Workspace panes") — **not** a row of independently-tabbable buttons. Grouping into a toolbar