docs(mcp): add 10-agent research on scene-save workflow

10 parallel research agents (R1-R10) investigated whether MCP can save
scenes as saveable entities that the user later opens in the editor —
rather than injecting via a dev-only window.__pascalScene hook.

Key findings:
- Editor is already backend-agnostic via onLoad/onSave callbacks (R2,R7)
- Current persistence is localStorage-only, single key (R1)
- Zero dynamic routes and no backend code yet — env declared (R4,R5)
- File import exists as "Load Build" but lacks Zod validation (R6)
- MCP-written scenes load cleanly into the editor today (R6, Casa del
  Sol test already proved this)
- Best path: filesystem-handoff this week, Supabase in weeks 2-4,
  Supabase Realtime for live mode in Q2. Skip Yjs for now. (R8)
- 4-5 weeks to private beta, 10-14 to GA (R9)
- 10 high-value ideas ranked; "photo -> scene" is the unblocker (R10)

SYNTHESIS.md pulls all 10 reports together with the recommended
implementation plan.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/mcp/test-reports/research/R1-persistence.md

@@ -0,0 +1,49 @@
+# R1 — Persistence layer
+
+## TL;DR
+- **Scene data:** single-key localStorage, `pascal-editor-scene`, shape `{ nodes, rootNodeIds }`. Written by the autosave hook with 1 s debounce; flushed on `beforeunload`.
+- **UI preferences, viewer prefs, audio:** three separate Zustand-persist stores, each with its own localStorage key.
+- **Asset binaries (textures):** IndexedDB via `idb-keyval`, keys `asset_data:<uuid>`.
+- **Backend persistence:** NONE in this repo. No Supabase calls, no API routes for scenes, no database integration.
+- **Scene identity / listing:** NONE. One scene per origin per browser.
+
+## Write pathways
+
+| When | What | Where |
+|---|---|---|
+| 1 s after any scene mutation | `{ nodes, rootNodeIds }` → `onSave` callback (if provided) else `localStorage['pascal-editor-scene']` | `packages/editor/src/hooks/use-auto-save.ts:104–135` |
+| Every UI state mutation | `pascal-editor-ui-preferences` | Zustand persist in `use-editor.tsx:372–607` |
+| Every viewer state mutation | `viewer-preferences` | Zustand persist in `use-viewer.ts:81–220` |
+| Every audio state mutation | `pascal-audio-settings` | `use-audio.tsx:22–43` |
+| On `beforeunload` | Final scene snapshot | `use-auto-save.ts:137–147` |
+
+## Read pathways
+
+1. **Editor mount** (`editor/index.tsx:765–796`):
+   - If host supplied `onLoad` → `await onLoad()`
+   - Else → `loadSceneFromLocalStorage()`
+   - Apply via `useScene.setScene(nodes, rootNodeIds)`
+2. **Selection hydration** — `syncEditorSelectionFromCurrentScene()` (`lib/scene.ts:251–332`)
+3. **Zustand persist** hydrates UI/viewer/audio stores automatically on first subscriber
+
+## What's NOT persisted
+- Undo/redo history (`useScene.temporal` — in-memory only)
+- Active tool state (`movingNode`, `editingHole`, `curvingWall`)
+- Camera position/rotation
+- Collections (stored in nodes array but not in the persist partialize)
+- Three.js mesh/material cache
+
+## Multi-scene support
+- Single global key `pascal-editor-scene`. No scene id, name, thumbnail, version.
+- `projectId` prop scopes UI **selection** (building/level/zone) but NOT scene data.
+- No listing, no metadata, no per-project isolation of the scene itself.
+
+## Gap to "MCP writes → user opens saved scene"
+Needs:
+1. Scene entity layer: id, name, projectId, created_at, thumbnail_url.
+2. Backend table (or filesystem for local dev).
+3. MCP tools for scene lifecycle (`save_scene`, `list_scenes`, `load_scene`, `delete_scene`).
+4. Editor route `/scene/[id]` that reads scene by id on mount.
+5. Host-app `onLoad(() => fetchScene(sceneId))`.
+
+Foundation is solid — `SceneGraph` type + `applySceneGraphToEditor` are production-ready; only the entity layer is missing.