Web Frontend

• No forwardRef — ref is a regular prop in React 19. Declare it in the props type and destructure it directly.
• No ElementRef — use React.ComponentRef<typeof SomeComponent> instead (the ElementRef alias is deprecated).
• No gratuitous useMemo / useCallback / React.memo — the React Compiler (enabled in the build) auto-memoizes. Only add manual memoization when profiling shows a concrete bottleneck; remove existing wrappers when they have no measured benefit.
• Prefer use() for consuming promises and context where appropriate.

// ❌ Deprecated React 18 pattern
const Input = forwardRef<ElementRef<typeof Primitive>, InputProps>(({ className, ...props }, ref) => (
  <Primitive ref={ref} {...props} />
))
Input.displayName = "Input"

// ✅ React 19 — ref is a regular prop
function Input({ className, ref, ...props }: InputProps & { ref?: React.Ref<React.ComponentRef<typeof Primitive>> }) {
  return <Primitive ref={ref} {...props} />
}

Components

• Always use Text from @repo/ui for text content
• Always use Button from @repo/ui for buttons
• Do not nest Text inside Button. Button already sets font size, weight, and color; use plain text (and optional icons) as direct children. Wrapping the label in Text duplicates styles (e.g. avoid <Button><Text.H5>Save</Text.H5></Button>).
• Lucide icons: import from lucide-react and pass the component to @repo/ui’s Icon via the icon prop (e.g. <Icon icon={Pencil} size="sm" />). Prefer that over raw <Pencil /> so shared sizing and color tokens apply. Buttons and other primitives that accept an icon prop follow the same pattern; otherwise wrap with Icon.
• Always use GoogleIcon and GitHubIcon from @repo/ui for OAuth provider icons

Route-level component organization

Place React components close to the routes that use them, inside a -components/ subfolder within the route directory. This keeps route files (which TanStack Router auto-discovers) clearly separated from supporting components.

routes/_authenticated/projects/$projectId/datasets/
├── index.tsx                       # route file
├── $datasetId.tsx                  # route file
└── -components/                    # supporting components for these routes
    ├── dataset-table.tsx
    ├── row-detail-panel.tsx
    └── version-badge.tsx

• Route files live directly in the route directory — TanStack Router discovers them
• Supporting UI for those routes lives in the adjacent -components/ folder
• domains/ directories (apps/web/src/domains/) are for state management only: server functions (writes) and collections/queries (reads) — not UI components

Design system showcase

• When adding a new implemented UI component in packages/ui (or replacing a placeholder export with a real implementation), update apps/web/src/routes/design-system.tsx to include a usage example for that component in both light and dark mode previews.
• Treat apps/web/src/routes/design-system.tsx as the canonical visual inventory for @repo/ui components.

State management (TanStack)

The web app uses a server-centric, query-driven architecture built on the TanStack ecosystem. No Zustand, Redux, or global stores.

Server functions — All data fetching and mutations use createServerFn from @tanstack/react-start:

import { Effect } from "effect"
import { ProjectRepository, createProjectUseCase } from "@domain/projects"
import { ProjectRepositoryLive, SqlClientLive } from "@platform/db-postgres"
import { getPostgresClient } from "../../server/clients.ts"

// Query (GET)
export const listProjects = createServerFn({ method: "GET" }).handler(async () => {
  const { organizationId } = await requireSession()
  const client = getPostgresClient()

  return await Effect.runPromise(
    Effect.gen(function* () {
      const repo = yield* ProjectRepository
      return yield* repo.findAll()
    }).pipe(
      Effect.provide(ProjectRepositoryLive),
      Effect.provide(SqlClientLive(client, organizationId)),
    ),
  )
})

// Mutation (POST) with Zod validation
export const createProject = createServerFn({ method: "POST" })
  .inputValidator(createProjectSchema)
  .handler(async ({ data }) => {
    const { userId, organizationId } = await requireSession()
    const client = getPostgresClient()

    return await Effect.runPromise(
      createProjectUseCase({...}).pipe(
        Effect.provide(ProjectRepositoryLive),
        Effect.provide(SqlClientLive(client, organizationId)),
      ),
    )
  })

Server functions live in apps/web/src/domains/*/functions.ts.

Collections — Client-side reactive state uses TanStack React DB + Query via queryCollectionOptions:

const projectsCollection = createCollection(
  queryCollectionOptions({
    queryClient,
    queryKey: ["projects"],
    queryFn: () => listProjects(),
    getKey: (item) => item.id,
    onInsert: async ({ transaction }) => { /* optimistic insert */ },
    onUpdate: async ({ transaction }) => { /* optimistic update */ },
    onDelete: async ({ transaction }) => { /* optimistic delete */ },
  }),
)

export const useProjectsCollection = (...) => useLiveQuery(...)

Collection files live in apps/web/src/domains/*/collection.ts.

Route middleware vs route data

• Use beforeLoad for middleware-style checks that should block the route tree early: auth redirects, authorization gates, and other preconditions.
• Use loader for data the route or layout actually renders. This keeps rendered data in TanStack Router's loader lifecycle, so it can use staleTime, useLoaderData({ select }), and avoid unnecessary refetching on same-route search-param navigations.
• If the same lookup is both your guard and your rendered data source, prefer doing that work in loader once instead of duplicating it across beforeLoad and loader.
• When multiple descendant routes need parent loader data, prefer a small route-scoped wrapper around getRouteApi("...") instead of repeating the route id string in every file.

export const Route = createFileRoute("/admin")({
  beforeLoad: async () => {
    const session = await getSession()
    if (!session?.user.isAdmin) throw redirect({ to: "/" })
  },
})

export const Route = createFileRoute("/_authenticated")({
  staleTime: Infinity,
  loader: async () => {
    const session = await getSession()
    if (!session) throw redirect({ to: "/login" })

    const sessionData = session.session as Record<string, unknown>
    const organizationId =
      typeof sessionData.activeOrganizationId === "string" ? sessionData.activeOrganizationId : null
    if (!organizationId) throw redirect({ to: "/welcome" })

    return {
      user: session.user,
      organizationId,
    }
  },
})

const authenticatedRoute = getRouteApi("/_authenticated")

export function useAuthenticatedUser() {
  return authenticatedRoute.useLoaderData({ select: (data) => data.user })
}

Key rules:

• Server functions are the only data-fetching mechanism — no direct REST API calls from the client
• Use collections for reactive, queryable client state with automatic server sync
• Use useState for local UI state (modals, form visibility); no global stores
• Invalidate query cache after mutations: getQueryClient().invalidateQueries({ queryKey: [...] })
• Forms use TanStack React Form (useForm + form.Field)

TanStack Form + Zod field errors (createFormSubmitHandler + fieldErrorsAsStrings)

When: useForm submits work that can fail with Zod validation (for example server functions using inputValidator), and you want inline errors on @repo/ui fields (not only a toast).

Module: apps/web/src/lib/form-server-action.ts

Always use both when you want Zod-driven field errors: the submit handler wires errors into form state; the helper wires form state into @repo/ui.

Do not duplicate the inline pattern field.state.meta.errors.length > 0 ? field.state.meta.errors.map(String) : undefined — use fieldErrorsAsStrings instead.

Reference: apps/web/src/routes/_authenticated/index.tsx — RenameProjectModal: createFormSubmitHandler in useForm (~line 225), fieldErrorsAsStrings on the name field Input (~line 287).

Layout and spacing

• Always use flexbox for layout (flex, flex-col, flex-row)
• Never use margin utilities (no m-*, mx-*, my-*, mt-*, etc.)
• Always use gap utilities for spacing between elements (gap-*, gap-x-*, gap-y-*)
• Always use p-* (padding) for internal spacing within containers

Conditional classes (cn)

With cn(), use object syntax { "class-name": condition } — not short-circuit condition && "class-name".

// ❌ Bad
<div className={cn("base-class", isActive && "bg-accent")} />

// ✅ Good
<div className={cn("base-class", { "bg-accent": isActive })} />

Example

// ❌ Bad - using margins and space-y
<div className="space-y-4 mt-4">
  <div className="mb-2">Item 1</div>
  <div className="mb-2">Item 2</div>
</div>

// ✅ Good - using flexbox with gap
<div className="flex flex-col gap-4 pt-4">
  <div>Item 1</div>
  <div>Item 2</div>
</div>

React effects (useEffect policy)

• Do not call useEffect directly in components; use useMountEffect from @repo/ui for mount/unmount-only sync (listeners, imperative widgets, one-time setup).
• If raw useEffect is unavoidable, add TODO(frontend-use-effect-policy) with a short reason.

Prefer: derive values during render; run work in event handlers; controlled vs uncontrolled via value !== undefined; reset by key when an entity id changes.

Avoid: deriving state from props in an effect; fetching in effects to set state; mirroring props into local state; effects as command dispatchers.

import { useMountEffect } from "@repo/ui"

useMountEffect(() => {
  const cleanup = subscribeToExternalSystem()
  return () => cleanup()
})