RQ7 — Which data uses the server cache, which uses TanStack Query, how is each invalidated?

Question (BRIEF.md RQ7, G6.5): which data classes use the Next.js server cache and which use TanStack Query, and how is each invalidated after a CRUD write? Evidence: one entity.

Answer: cache by data class, not by page. Static config and org settings live in the server cache with tags. Entity lists and details live in TanStack Query with keys that start with the org. After a write, invalidate both sides: revalidateTag on the server and queryClient.invalidateQueries on the client.

Data class table

Key shape rule: every org-scoped key starts ['org', orgId, ...] (tanstack5 rule in VERSIONS.md). One queryKeys factory per entity builds them; no inline key arrays.

Invalidation after a CRUD write (one entity)

1. Client calls the entity client (ADR 0006 factory, side: 'client') → /api/v1/... BFF.
2. Optimistic variant: onMutate writes setQueryData; onError rolls back. Pessimistic variant: wait for the response (G8.4 asks for both).
3. On success, the client calls invalidateQueries({ queryKey: ['org', orgId, entity] }).
4. Server-cached data touched by the write (settings, config) is revalidated server-side in the Route Handler with revalidateTag(tag). The client never asks the server to revalidate by name.
5. Other tabs and users get the change through SSE (event → invalidateQueries), not polling.

Rules

• No user data in 'use cache' unless the org id is part of the cache key and the tag.
• Session reads are never inside 'use cache' (they read cookies()).
• The server QueryClient is per request (cache()); the browser one is one per tab.
• No useEffect + fetch for data (frontend-layout D6 review blocker).

Sources

• Next.js cacheTag / revalidateTag / 'use cache' (Cache Components, VERSIONS.md next16).
• TanStack Query invalidation — https://tanstack.com/query/latest/docs/framework/react/guides/query-invalidation.
• ddx-nextjs-frontend-layout D3, D6, D8.

• ddx-documentation — dudoxx-web-boot

adr/

• ADR 0001 — Scaffold route: dudoxx-sandbox-creator with 163XX overrides
• ADR 0002 — Auth: better-auth 1.7 in ddx-api
• ADR 0003 — Route shape: org slug, role, [entity]/[id], ?view=
• ADR 0004 — Database split: one Postgres 18 instance, six databases
• ADR 0005 — Frameworks and the approved dependency table
• ADR 0006 — API clients come from one factory
• ADR 0007 — Typed service container (DI / IoC)
• ADR 0008 — Singleton scope: what may live at module level
• ADR 0009 — One variant API for every inventory component
• ADR 0010 — Media path: presigned URLs from ddx-api after the org check
• ADR 0011 — Media proxy: MinIO only through ddx-api
• ADR 0012 — Density names: compact | cosy | large
• ADR 0013 — Platform super-admin acts as org-admin of the target org
• ADR 0014 — Unified settings: one registry, three tiers, one resolve in ddx-api
• ADR 0015 — Entity kernel: one descriptor, one access seam, one projection, one proof chain
• ADR 0016 — SSE Bus: Redis Streams log, Redis pub/sub fan-out, BullMQ outbound queue
• ADR 0017 — Layered BFF: one route table, route classes, read models
• ADR 0018 — Cluster node registry, node identity, hot plug
• ADR 0019 — Tenant branding: settings keys, vendored palettes, public platform read
• Debug overlay

deploy/

• Deploy runbook — dudoxx-web-boot
• Entity kernel — guide
• Feature map — what each role can do
• Component inventory
• Naming constitution — dudoxx-web-boot
• Observability — one log layout, one key set
• Pattern reference — P1-P23 and groups A-K
• Port map — dudoxx-web-boot

research/

• RQ1 — Which release is "latest", and does it differ from the canon?
• RQ10 — SSE through the Next.js BFF route handler (desk half)
• RQ11 — Dev latency baseline: cold compile per route + next-server RSS
• RQ2 — Route group or dynamic org slug?
• RQ3 — better-auth 1.7 vs Auth.js v5: feature matrix
• RQ4 — Separate databases or separate schemas?
• RQ5 — Which frameworks beyond shadcn earn a place?
• RQ6 — How do DI, IoC and Singleton behave across RSC, client bundles and NestJS?
• RQ7 — Which data uses the server cache, which uses TanStack Query, how is each invalidated?
• RQ8 — Media path: presigned URLs vs streaming through the BFF
• Template triage — create-nextjs code in ddx-web
• Settings — guide
• Local setup — dudoxx-web-boot
• Shell tree — SiteShell and PortalShell
• SSE event catalog
• Version pins — dudoxx-web-boot