Mutations and Server Actions

Treat every Server Action like an exposed server operation

A button being hidden does not protect the operation behind it. Validate the input and check the caller inside the action or inside the server-side domain function it invokes.

A reliable mutation sequence is boring on purpose: authenticate, authorise, validate, write, invalidate, then redirect or return a typed result.

Keep the write path obvious

'use server'

export async function updateProject(formData: FormData) {
  const user = await requireUser()
  const input = projectSchema.parse(Object.fromEntries(formData))
  await requireProjectPermission(user, input.id)

  await saveProject(input)
  updateTag(`project:${input.id}`)
  updateTag('projects')
  redirect(`/projects/${input.slug}`)
}

Validation errors are normal results

Bad form input is not an infrastructure failure. Return field-level information the UI can display near the relevant control instead of throwing everything into an error boundary.

Reserve thrown exceptions for failures the current flow cannot reasonably handle.

Forms are still useful without turning everything into client state

Server Actions work naturally with forms. Keep the server mutation independent from cosmetic client behaviour, then add pending state and optimistic UI only where they improve the experience.

Do not build a client-side state machine for a simple form just because the framework allows one.