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/R4-routing.md

@@ -0,0 +1,38 @@
+# R4 — Routing & URLs
+
+## TL;DR
+**Zero dynamic routes today.** Every user lands on `/` which hardcodes `projectId="local-editor"`.
+
+## Route tree
+```
+apps/editor/app/
+├── page.tsx            (Home: <Editor projectId="local-editor">)
+├── layout.tsx
+├── privacy/page.tsx
+├── terms/page.tsx
+├── api/health/route.ts
+└── fonts/
+```
+
+- No `[id]`, `[projectId]`, `[sceneId]`, or `[[...slug]]` segments.
+- No middleware.
+- No `rewrites()` / `redirects()` in `next.config.ts`.
+- No query-param driven state.
+- No hash routing.
+
+## Latent expectation (dead code)
+`packages/editor/src/components/ui/action-menu/view-toggles.tsx:79`:
+```ts
+const projectId = window.location.pathname.split('/editor/')[1]?.split('/')[0]
+```
+Code expects URLs of shape `/editor/<projectId>/…`. No such routes exist. Falls through to `undefined` gracefully today but signals a planned structure.
+
+## Options to add
+| Option | Route | Effort |
+|---|---|---|
+| A | `/?sceneId=<id>` — reuse `/` + `useSearchParams` | XS |
+| B | `/editor/[projectId]` | S |
+| C | `/editor/[projectId]/[sceneId]` | M |
+| D | `/scene/[id]` — flat, project-agnostic | S |
+
+Recommended: **B for projects, `/scene/[id]` short-link for sharing**. Matches the latent expectation in view-toggles.tsx.