Editor: composition structure wireframe (read-only)

docs/architecture/08-vega-editor-techniques.md

@@ -299,6 +299,11 @@ thin app-layer services.
 - `spec-insert` — the composition the cursor is in (`compositionTargetAt`), inserting a view
   at an index (`insertView`) and reordering siblings (`moveView`), plus `elementOffset` to
   re-find a view after the edit.
+- `spec-view-tree` — the whole composition as a recursive tree (`viewTree`), each node carrying
+  its operator, orientation and byte range. Read at once (vs. `spec-insert`'s one-array edits) to
+  drive the composition wireframe — a read-only schematic of the multi-view structure in a preview-
+  toolbar disclosure (`CompositionWireframe`); clicking a box reveals that view's range in the
+  editor via `AppStore.requestRevealView`. Interaction contract in [arch 10](10-interaction-and-feedback.md).
 
 **Services (app, store-aware via `getState`):** `spec-transform-actions` (the
 wrap/simplify/add-view operations and their surfaces), `spec-dataset-hints` (completion,