Phase 6 — Provider composer & data layer

[jonmatum]

Phase 6 — Provider composer & data layer

One import to wire up all the providers a consumer app needs, with opt-out / replace per slot.

Deliverables

• <AppProviders> composer nesting: ThemeProvider → QueryProvider → ToastProvider → ErrorBoundary → TooltipProvider → I18nProvider (optional)
• QueryProvider wrapping TanStack Query v5 with sensible defaults (retry, staleTime, SSR hydration helpers)
• ToastProvider wrapping Sonner, themed via tokens
• ErrorBoundary with fallback UI using ErrorState
• I18nProvider thin wrapper — adapter pattern, defaults to no-op; consumers can plug next-intl or similar
• Each provider individually exported so advanced users can compose manually
• Query hydration helpers for Next.js 15 server components

Acceptance

• A consumer wraps <AppProviders> once and gets theme + data fetching + toasts + error handling working
• Any single provider is replaceable via prop override without forking the composer
• Zero hydration warnings in Next.js 15 strict mode

Depends on Phase 2.

Part of the next-shell app shell extraction plan.