docs(plan6): note deferred localStorage first-paint mirror as follow-up

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/superpowers/specs/2026-06-02-void-v2-plan6-sacred-valley-design.md

@@ -216,3 +216,10 @@ Security: confirm the health checker rejects targets outside the registry.
 - Multi-host metrics; per-agent theming; final avatar art; agent-output cards.
 - Optional: pre-seed/vendor the icon cache at deploy (fully offline, no first-use
   CDN fetch) and a periodic refresh.
+- **Deferred from the alpha-8 build (final-review follow-ups):** the §4.4
+  localStorage first-paint mirror was not implemented — the dashboard fetches the
+  server layout before mounting, so a brief default-order paint can occur on slow
+  links. Implementing it well needs an async restructure of `sacred_valley.js`
+  (mount from cache synchronously, then reconcile with the server). Also optional:
+  a unit test asserting the health checker only receives registry-sourced services
+  (the guarantee is structural today).