Next.js App Architecture

This repository (Asymmetric-al/core)

Subordinate to installed Next.js docs (apps/<app>/node_modules/next/dist/docs/ or .next-docs/), docs/ai/rules/frontend.md, docs/ai/skills/nextjs-app-router/SKILL.md, docs/ai/skills/cache-components/SKILL.md, and docs/guides/architecture/data-access-boundary.md.

Apply only to the requested scope. An audit does not authorize a repository-wide async-page refactor. Core's Stream / Cache / explicit Block decisions remain controlling; synchronous composition is this skill's default, not a ban on deliberately qualified async routes.

This skill is for page composition, Suspense placement, leaf client boundaries, and feature-owned UI. It is not a license to invent a new app folder scheme or move business database logic.

Repo mapping:

• Privileged reads, writes, payments, webhooks, and vendor calls stay in packages/api.
• Browser-visible table data uses @asym/database/hooks only in 'use client' leaves when a collection exists. Async Server Components call published server-read subpaths instead.
• Shared UI stays in @asym/ui / exact base-maia. Existing apps/*/features/ directories are UI composition, not a new query layer.
• All apps already run cacheComponents: true and partialPrefetching: true. Do not "enable Cache Components." Follow Instant Navigation (Stream / Cache / explicit Block) in docs/ai/rules/frontend.md.
• Get API mechanics from the installed Next.js docs, not preview.nextjs.org or remembered APIs.
• Do not add Zustand. Use the installed TanStack Query / TanStack DB patterns from docs/ai/rules/frontend.md.
• Do not regenerate or expand the managed root AGENTS.md.

Core remaps — apply these at every numbered step. Upstream file-placement lines are vendor text, not permission to add a query layer.

• Feature-owned means UI composition only. Server feature components select a published @asym/api/* read; client leaves use approved browser hooks or API routes. A plain server helper is not a callable Server Action. Do not create features/<domain>/<domain>-queries.ts or features/<domain>/<domain>-actions.ts at all.
• Mutation boundary: A client leaf calls an existing approved hook/API route, or an authenticated 'use server' adapter in an established app boundary that validates input and delegates business work to packages/api. It never directly imports an ordinary API server command.
• Cache ownership: Server tags and invalidators stay in packages/api/src/shared/cache-tags.ts or their API-owned domain module. Feature-local files own browser query keys/options only; coordinate the two explicitly without an API-to-app import.
• Prerequisite: Prefer the project's installed Next.js docs (apps/<app>/node_modules/next/dist/docs/ or .next-docs/). Do not create or refresh root AGENTS.md from preview.nextjs.org.

Refresh: references/upstream.md.

A workflow for building and auditing Next.js 16+ App Router apps so they follow one consistent, feature-sliced RSC architecture like next-beats.

Follow the workflow below step by step — apply the Core remaps at each step. Upstream *-queries.ts / *-actions.ts lines are vendor text: CORE: skip file creation. Load the reference a step names for the decision it depends on. Get framework mechanics (API signatures, config options, hook contracts) from the linked docs — don't restate or improvise them.

Prerequisite

Before changing a Next.js app, read version-matched docs from apps/<app>/node_modules/next/dist/docs/ or .next-docs/. Do not create or refresh root AGENTS.md from preview.nextjs.org. Then use this skill for architecture decisions.

Architecture target

Build pages that describe the loading experience, not pages that act like route loaders:

• app/**/page.tsx and layout.tsx are synchronous composition surfaces: static chrome, section headings, <Suspense> boundaries, error boundaries, and transition wrappers.
• Feature components own their reads on the server. They receive minimal stable inputs (id, slug, handle, parsed filter values) or already-fetched records, never raw params / searchParams.
• Queries and actions live in the feature folder. Components import queries; client leaves import actions directly. (CORE: skip file creation. Server components call published API read subpaths; client leaves use approved browser hooks/API routes or authenticated Server Action adapters.)
• When server tags and client query keys describe the same feature data, a pure feature-local cache contract owns those identities. (CORE: server tags remain API-owned; feature-local contracts own browser keys only, with explicit coordination.)
• Stable chrome, wrappers, and skeletons preserve layout: cards/panels stay outside Suspense, and fallbacks swap only the data-dependent body.

Invariants (what every change must satisfy)

The non-negotiables. The workflow produces them; the final check verifies them.

1. Pages compose, they never fetch. A page/layout imports feature components and places <Suspense>. No queries or domain logic inline. Tiny route-local control-flow helpers are allowed only when they exist to place a boundary around connection(), redirect(), or a resolved route prop.
2. Pages stay synchronous. Use params.then() / searchParams.then() or Promise.all([params, searchParams]).then(...), never await params at the top — so chrome paints into the static shell and only data-dependent sections suspend.
3. Feature components receive IDs, not route props. Resolve params / searchParams at the page boundary and pass plain values (id, slug, query) into features.
4. Async server component is the default. 'use client' only for hooks, event handlers, or browser APIs — and only on leaves, never on parents of server content.
5. The page owns the Suspense boundary; the feature owns the skeleton. Features never pre-wrap themselves in <Suspense>; stable wrappers/cards/chrome wrap the boundary instead of being duplicated in fallback and final content.
6. Skeletons live in the same file as the component, exported alongside it, defined at the end. Feed and FeedSkeleton are siblings.
7. Queries live in <domain>-queries.ts (import 'server-only'); actions live in <domain>-actions.ts ('use server'). The file name matches the folder, even for sub-concepts. (CORE: skip file creation. Server reads use published @asym/api/* subpaths; browser hooks run only in client leaves, and mutations cross a supported callable boundary. Do not add those files under apps/*/features/.)
8. Feature folders follow product ownership. Entity-owned sub-concepts (favorite, like, vote, bookmark) fold into their parent. A route-level experience that composes multiple domains may own its UI and state in a separate feature while each domain keeps its queries and actions. (CORE: "keeps its queries and actions" means packages/api, not a feature-local query file.)
9. Client components import actions directly — never receive a server action as a prop just to call it. (CORE: direct action imports require a real 'use server' boundary; otherwise call the approved hook/API route. Ordinary packages/api commands stay server-side. Follow installed Next.js docs for valid action-prop composition.)
10. Feature-local cache coordination stays with its domain. Put pure tags/keys in <domain>-cache.ts, client query definitions in <domain>-query-options.ts, hook wrappers in hooks/use-*.ts, and tiny client leaves in components/; promote support code only after real cross-feature reuse. (CORE: only browser keys/options are feature-local; server tags and invalidation stay API-owned and never import an app feature.)
11. Interactive async UI keeps server data on the server and client state local to the interaction. Use useOptimistic, useTransition, reducers, URL/search params, and form actions instead of mirrored prop state, derived-state effects, or hand-rolled pending arrays.

Workflow

Run these in order for build-from-scratch, feature work, or audits. Each step names the reference to consult and the check it must pass.

1. Choose mode.
   • Build from scratch: sketch routes, real domain nouns, static shell, and expected loading groups before writing code.
   • Audit/refactor: scan current app/ pages first; list every async page, page-level query import, route prop leak, missing Suspense boundary, and feature folder mismatch. → references/example.md for the target shape; references/feature-folders.md for placement. ✓ You know whether you are creating the architecture or converting loader-shaped code into it.
2. Place the work. Decide the feature folder before writing anything. → references/feature-folders.md (decision tree + merge rules). ✓ A real domain, a cross-domain product experience, or folded into the right parent.
3. Write the query and, when a client cache shares its data, the cache contract. Put server reads in <domain>-queries.ts with import 'server-only'; keep shared tag/key identities in a pure <domain>-cache.ts. (CORE: skip file creation. Async Server Components call an existing published API read subpath; only 'use client' leaves call @asym/database/hooks for an approved browser table. Keep server tags API-owned and browser query keys in the client owner.) → references/queries-actions.md; for SWR/TanStack Query → references/single-page-applications.md; with cacheComponents: true, also → references/cache-components.md. ✓ Cache identities are defined once; server reads are server-only, cached/tagged/lifetimed under Cache Components, and return domain types rather than ORM rows.
4. Write the action (if there's a mutation). features/<domain>/<domain>-actions.ts, 'use server' at the top. (CORE: skip file creation. Client mutations use an approved hook/API route or authenticated 'use server' adapter in an established app boundary; that boundary delegates to the owning packages/api command. Do not import ordinary server commands into a client leaf.) → references/queries-actions.md. ✓ Re-checks auth, validates input, invalidates matching cache tags under Cache Components (refresh() only for justified dynamic reads), returns a discriminated union. Core: preserve the owning callable boundary's typed HTTP or Server Action result contract; the API owner invalidates its server tags.
5. Build the component + skeleton. features/<domain>/components/<name>.tsx: an async server component that awaits its own query from minimal props; 'use client' only on interactive leaves. (CORE: the async server owner calls a published @asym/api/* read; an approved database hook belongs in a separate 'use client' leaf, never in the async server owner. No new *-queries.ts.) → references/components.md; for a client data library or strict-SPA/CSR feature → references/single-page-applications.md. ✓ Component receives IDs/handles/parsed filters or already-resolved records, not params; skeleton is a sibling export at the end; no alias skeleton wrappers.
6. Compose the page. app/<route>/page.tsx: synchronous, params.then() / Promise.all(...).then(...), place Suspense around data bodies, and wrap fallible sections in an error boundary. → references/pages-suspense.md. ✓ Route props become plain values; stable cards/sections wrap Suspense when they set layout; boundaries stay visible at the page.
7. Add interaction (if any): optimistic updates, pending state, toasts, confirmation. → references/ux-patterns.md. ✓ Feedback isn't doubled; optimistic reducers/actions live with the feature; URL/search params own shareable state; client effects synchronize external systems, not derived React state.
8. Verify against the checklist below before declaring done.

Verify before done

Inspect the diff against every invariant — each is checkable by reading the changed files:

• No page/layout imports a *-queries file or defines reusable domain UI inline; any inline helper is route-local control flow only.
• Every page with params is synchronous and uses params.then() / searchParams.then() / Promise.all([params, searchParams]).then(...).
• Feature components receive plain IDs/handles/parsed filters or resolved records; no feature prop is named params or searchParams.
• Every <Suspense> for page data sits in the page; no feature pre-wraps itself.
• Stable wrappers/cards/chrome sit outside Suspense; fallback and final content do not duplicate the same outer card.
• Every component has its real *Skeleton in the same file, at the end; no tiny skeleton aliases just to pass props.
• Every *-queries.ts starts with import 'server-only'; every *-actions.ts with 'use server'. (CORE: skip file creation. A new *-queries.ts / *-actions.ts under apps/*/features/ means the change is wrong.)
• With cacheComponents: true, reusable reads use 'use cache' / cacheTag / cacheLife, or 'use cache: private' / 'use cache: remote' when appropriate; any dynamic read is intentional and justified.
• Mutations touching cached reads call updateTag() / revalidateTag(..., 'max') for the matching tags; refresh() is not a substitute for tag invalidation.
• Action files are named <folder>-actions.ts; no entity-owned sub-concept spawned its own folder, and cross-domain product features do not take ownership of entity queries/actions. (CORE: skip file creation.)
• Features with both server tags and client query keys define them once in a pure <domain>-cache.ts; queries, actions, hydration, query options, and hooks import from it. (CORE: server tags/invalidators stay API-owned; browser keys stay client-owned, and coordination never requires packages/api to import an app feature or duplicate server tag strings.)
• Feature-local client-support files sit in the smallest fitting place: query options at the feature root, use-* hook wrappers in hooks/, leaf components in components/, and shared support only after real cross-feature reuse.
• 'use client' components are leaves — they import actions/hooks/providers, not async server components.
• Client leaves use useOptimistic, transitions, reducers, URL state, or form actions for interaction; they do not call setState in effects for derived React state.
• Mutations validate their input and invalidate the affected data.

Reference index

• references/feature-folders.md — where code goes: folder layout, cache contracts, naming, and merging sub-concepts.
• references/queries-actions.md — query/action rules: server-only, dedup, validation, invalidation, return shape.
• references/components.md — server/client boundary, skeletons, use(), single-use helpers, live data.
• references/pages-suspense.md — page composition, params.then(), Suspense placement, CLS, error boundaries, prefetch.
• references/cache-components.md — the cacheComponents decisions: which reads to cache, which directive to use, how to invalidate.
• references/single-page-applications.md — client cache decisions: placement, server seeding, Cache Components coordination, hydration, and mutations.
• references/ux-patterns.md — interaction decisions: optimistic vs pending vs inline error, toasts, action-prop, confirmations.
• references/example.md — the next-beats reference app: invariant → file map, for seeing any rule in real code.