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/R3-scene-ui.md

@@ -0,0 +1,34 @@
+# R3 — Scene-management UI
+
+## What exists today
+
+| Feature | File | Line |
+|---|---|---|
+| "Save Build" → download `layout_YYYY-MM-DD.json` | `packages/editor/src/components/ui/sidebar/panels/settings-panel/index.tsx` | 205–216, 362–365 |
+| "Load Build" → file picker `.json` → `setScene` | `…settings-panel/index.tsx` | 218–239, 367–383 |
+| "Export Scene (JSON)" in command palette | `editor-commands.tsx` | 328–346 |
+| "Export GLB / STL / OBJ" | `export-manager.tsx` | — |
+| "Clear & Start New" destructive button | `settings-panel/index.tsx` | 427–434 |
+| "Explore scene graph" read-only tree dialog | `settings-panel/index.tsx` | 398–421 |
+| Autosave hook (1 s debounce → onSave or localStorage fallback) | `use-auto-save.ts` | 1–191 |
+| Scene-dirty tracking exposed to host via `onDirty` / `onSaveStatusChange` | `use-auto-save.ts` | 56–187 |
+
+## What's missing from a typical editor
+
+1. **New scene dialog with naming.** Saves are all date-stamped; no user-given names.
+2. **Scene list / picker.** No sidebar panel that lists saved scenes.
+3. **Open recent.**
+4. **Delete scene** (the destructive button clears current, can't delete a stored scene).
+5. **No `Ctrl+S` / `Cmd+S` save shortcut** registered in `use-keyboard.ts`.
+6. **No top-bar File menu.** `appMenuButton` slot exists for host to inject one, but nothing ships by default.
+
+## Where new UI should live
+
+- **Scene picker panel** via `extraSidebarPanels` prop — non-invasive, no Editor-core change.
+- **Quick actions** via `useCommandRegistry().register([...])` — `editor.scene.open`, `editor.scene.new`, `editor.scene.save-as`.
+- **Save-status badge** next to the navbar via `navbarSlot` (v2 layout).
+- **"Created by MCP" toast** via a new `Toast` provider in the editor's runtime init.
+
+## Verdict
+
+UI foundation is **~40%** of the way there. The infrastructure (autosave, callbacks, dialogs, palette extensibility) is all present. The missing pieces are UI-only: a scene-list panel (~150 LOC) + a few palette commands + a status indicator. No Editor core changes required if we keep it callback-driven and plug a host-side scene switcher.