docs(CLAUDE.md,ARCHITECTURE.md): record snapshot-consumer rollback (e142efd)

CLAUDE.md updates:
- Patterns to use: "useSessionSnapshots" section retitled "(OPT-IN)";
  the documented pilot adopters (useSessionInfo,
  AvatarInfoWidgetAvatarView) are removed. Adds explicit warning about
  the suspected useBetween + useSyncExternalStore + React Compiler
  interaction and the rollback in e142efd.
- Adopted table: snapshot-consumer row changed to "No in-tree
  consumers" with note about defensive fallbacks remaining.
- Not yet table: the useChatWidget reactive-ownUserId line corrected
  to reflect the rollback; the "migrate session-data mirrors" row
  marked BLOCKED with a retry hint (try a non-useBetween consumer
  first to isolate the cause).

ARCHITECTURE.md update:
- useExternalSnapshot bullet in the "Solution" section gains a note
  pointing at the 8 pre-built consumers in useSessionSnapshots.ts and
  the 2026-05-18 rollback caveat with the suspected interaction and
  retry guidance.

Pure documentation refresh; no code change. The useSessionSnapshots.ts
file and the vite alias remain in place — they're not what got rolled
back, only the consumer-side migrations were.

docs/ARCHITECTURE.md

@@ -103,7 +103,21 @@ information when forced into a single selector.
   `useSyncExternalStore` wrapper pairing the renderer's
   `EventDispatcher.subscribe()` with the `getXxxSnapshot()` getters
   added in renderer 2.1.0. Use this for readonly views over manager
-  state (`getUserDataSnapshot`, `getActiveRoomSessionSnapshot`).
+  state. Eight pre-built consumers live in
+  `src/hooks/session/useSessionSnapshots.ts` (userData / activeRoomSession
+  / ignoredUsers / groupBadges / soundVolumes / roomUserList + scalar
+  derivations `useIsUserIgnored`, `useGroupBadge`), each with defensive
+  `typeof` guards against a stale renderer bundle.
+
+  **Note (2026-05-18):** the first three pilot migrations (`useSessionInfo`,
+  `useChatWidget.ownUserId`, `AvatarInfoWidgetAvatarView` Ignore-menu)
+  were rolled back in `e142efd` after a persistent runtime error
+  `(intermediate value)() is undefined` at `ToolbarView.tsx:46` that
+  the vite-alias fix (`790ad2b`) and defensive guards (`c35a2d4`) could
+  not eliminate. Suspected interaction: `useBetween` +
+  `useSyncExternalStore` + React Compiler. Before retrying any
+  migration here, exercise the snapshot hooks from a non-`useBetween`
+  consumer in a low-blast-radius widget first to isolate the cause.
 
 For state owned outside the listener (the `useState` + `setState(prev =>
 applyX(prev, event))` pattern), keep using `useNitroEvent` /