feat(mcp,editor): Option A+B storage + 10 agent deliverables (Phase 7)

Ships the combined filesystem/Supabase storage adapter + MCP scene
lifecycle tools + Next.js API routes + editor /scene/[id] route, so
an MCP save is directly openable at /scene/<id> without any
injection hack. End-to-end verified: 10/10 e2e steps pass.

Storage (A1/A2/A3):
- SceneStore interface + error classes + slug helpers
- FilesystemSceneStore at $PASCAL_DATA_DIR (defaults XDG/~/.pascal)
  with atomic writes, .index sidecar, optimistic locking
- SupabaseSceneStore with scenes + scene_revisions tables, RLS
  migration SQL, mock-backed unit tests
- createSceneStore(env) auto-selects based on SUPABASE_URL +
  SUPABASE_SERVICE_ROLE_KEY

MCP tools (A4, A8, A9, A10):
- save_scene / load_scene / list_scenes / delete_scene / rename_scene
- list_templates / create_from_template (3 seed templates:
  empty-studio, two-bedroom, garden-house)
- generate_variants (7 mutation kinds, seeded RNG, save=true|false)
- photo_to_scene (vision sampling → scene graph → save)

Editor (A5, A6):
- /api/scenes + /api/scenes/[id] with RFC 7232 If-Match locking
- /scene/[id] and /scenes route pages with save button, SceneLoader
- Removed the window.__pascalScene dev injection hack

Security + UX edges (A7, A8):
- AssetUrl Zod validator: asset:// blob: data:image/ /path https:
  (http://localhost for dev) + PASCAL_ALLOWED_ASSET_ORIGINS env
  allowlist. Hardens scan.url, guide.url, item.asset.src,
  material.texture.url, MaterialMaps.*Map
- Auto-frame camera on empty→non-empty scene transition
  (camera-controls:fit-scene emitter event)

Shared utilities:
- rehydrateSiteChildren() extracted to packages/mcp/src/lib/ and
  used by both create-from-template and generate-variants to work
  around the SiteNode.children-as-objects vs. ids inconsistency
  (CROSS_CUTTING §2)
- Storage + MCP subpath exports added to packages/mcp/package.json
  (CROSS_CUTTING §4)

Tests: 293 pass / 0 fail across 40 files (was 142 pre-Phase-7).
Biome: clean.

Phase-7 e2e script at packages/mcp/test-reports/phase7-e2e.ts:
MCP HTTP + editor Next.js both point at $PASCAL_DATA_DIR =
/tmp/pascal-e2e, save_scene from MCP, GET /api/scenes/<id> from
editor server, /scenes list page renders all saved scenes, scene
page renders SceneLoader, delete_scene works.

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

packages/mcp/src/tools/scene-lifecycle/delete-scene.ts

@@ -0,0 +1,50 @@
+import type { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js'
+import { z } from 'zod'
+import { SceneNotFoundError, type SceneStore, SceneVersionConflictError } from '../../storage/types'
+import { ErrorCode, throwMcpError } from '../errors'
+
+export const deleteSceneInput = {
+  id: z.string().min(1).max(64),
+  expectedVersion: z.number().int().positive().optional(),
+}
+
+export const deleteSceneOutput = {
+  deleted: z.boolean(),
+}
+
+export function registerDeleteScene(server: McpServer, store: SceneStore): void {
+  server.registerTool(
+    'delete_scene',
+    {
+      title: 'Delete scene',
+      description:
+        'Delete a scene from the SceneStore by id. Optionally pass `expectedVersion` for optimistic concurrency.',
+      inputSchema: deleteSceneInput,
+      outputSchema: deleteSceneOutput,
+    },
+    async ({ id, expectedVersion }) => {
+      try {
+        const deleted = await store.delete(id, {
+          ...(expectedVersion !== undefined ? { expectedVersion } : {}),
+        })
+        const payload = { deleted }
+        return {
+          content: [{ type: 'text' as const, text: JSON.stringify(payload) }],
+          structuredContent: payload,
+        }
+      } catch (err) {
+        if (err instanceof SceneNotFoundError) {
+          throwMcpError(ErrorCode.InvalidParams, 'scene_not_found', { id })
+        }
+        if (err instanceof SceneVersionConflictError) {
+          throwMcpError(ErrorCode.InvalidRequest, 'version_conflict', {
+            id,
+            expectedVersion,
+          })
+        }
+        const msg = err instanceof Error ? err.message : String(err)
+        throwMcpError(ErrorCode.InternalError, msg)
+      }
+    },
+  )
+}