Document persistence failure-surfacing and overlay-store conventions

docs/architecture/01-state-and-stores.md

@@ -162,6 +162,20 @@ Each cohesive feature owns a store holding its durable domain state.
 - **`useSettingsStore`** — user preferences (editor options, render debounce,
   date format, theme); mirrors what gets persisted to `localStorage`.
 
+### Global overlay stores (imperative trigger)
+
+Some surfaces are summoned from anywhere — including non-React code — and own only
+ephemeral request state, not durable data:
+
+- **`useConfirmStore`** — the blocking confirm dialog (the `window.confirm` replacement).
+- **`useNotificationStore`** — non-blocking toasts (failed saves, etc.).
+
+Each pairs its store with a thin **imperative trigger** exported alongside the hook —
+`confirm(opts): Promise<boolean>` and `notify(opts): string` — so orchestration/services can
+raise one without a hook: `export const notify = (o) => useNotificationStore.getState().notify(o)`.
+Components subscribe to the store to _render_ it; everyone else calls the function. (Why a
+toast at all, and which channel for which message: [10 · Interaction & Feedback](10-interaction-and-feedback.md) §1.)
+
 ### The central `useAppStore`
 
 `useAppStore` holds only _cross-cutting, ephemeral UI state_ that no single