Editor: interactive composition wireframe — drag to reorder and restructure

Drag a view's box (or Alt+up/down) to reorder it within its container; drag onto another view's edge to pair the two in a new row/column, move across containers, or insert. Each leaf shows a glyph of its mark type.

Core: spec-restructure.wrapViews (wrap, with flatten-to-insert, collapse, and data-pin invariants) and spec-insert.moveViewTo; the editor applies every drag as one undoable edit via AppStore.composeRequest, keeping the editor the single text source.

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

@@ -297,13 +297,24 @@ thin app-layer services.
 - `spec-inline-data` — the rows a specific `data` binding carries for profiling
   (`rowsForDataBinding`: inline `values`, or a self-defined `datasets` entry).
 - `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.
+  at an index (`insertView`) and reordering siblings (`moveView` swaps a neighbour, `moveViewTo`
+  slides to any index), plus `elementOffset` to re-find a view after the edit. It also owns the
+  shared `SpecPath` walkers (`valueAtPath`/`arrayAtPath`/`isPrefixPath`) — a module navigating a
+  path reuses these rather than re-inlining the array/object descent.
 - `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).
+  drive the composition wireframe — a 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`, and on the draft it is **drag-editable** (reorder + restructure).
+  Interaction contract in [arch 10](10-interaction-and-feedback.md).
+- `spec-restructure` — the path-targeted cross-container moves behind the wireframe's drag.
+  `wrapViews(target, source, axis, side)` pairs the dragged source beside the drop target in a new
+  concat (placed where the target was, the source removed), enforcing three invariants:
+  **flatten** a bare same-orientation concat nested directly in a concat (so a with-axis drop reads
+  as a plain _insert_, not redundant nesting), **collapse** the source's emptied container (unwrap a
+  one-child, drop a zero-child, recursing up the chain), and **data-pin** a source's inherited
+  `data` before it changes ancestor (`dataBindingAtPath`, so it never silently rebinds). Degenerate
+  drops — onto itself, its own ancestor/descendant, or the root — return null.
 
 **Services (app, store-aware via `getState`):** `spec-transform-actions` (the
 wrap/simplify/add-view operations and their surfaces), `spec-dataset-hints` (completion,
@@ -325,6 +336,13 @@ Decision rules:
 - **One edit path.** The lightbulb returns a `WorkspaceEdit` (no editor handle); the toolbar
   and palette use `executeEdits`. Both build the replacement through the same
   serialize-and-reindent step, bracketed by `pushUndoStop`, so ⌘Z restores the prior text.
+- **Wireframe restructuring is one core op + the editor's undo.** Every drag resolves to either
+  `moveViewTo` (reorder within one container) or `wrapViews` (everything else — wrap, cross-container
+  move, insert); the wireframe only _requests_ it (`AppStore.requestComposeMove`/`requestComposeWrap`)
+  and `SpecEditor` applies it through the same `executeEdits` + `pushUndoStop` path as the other
+  transforms, so a drag is one ⌘Z and the editor stays the single text source. `wrapViews` covers
+  wrap and insert with one operation because it flattens bare same-orientation nesting afterward; the
+  drag's edge-zone interaction model lives in [arch 10](10-interaction-and-feedback.md).
 - **Composition CodeLens is cursor-scoped.** It follows the view the cursor sits in —
   `＋ Add view above/below` at the view's edges and `↑/↓ Move` to reorder among its siblings —
   rather than one fixed button per composition array; an empty composition shows a single `＋ Add view`,