Explicit 501 Not Implemented responses are justified

An HTTP 501 with no explanation tells clients the endpoint exists but does nothing, with no context on when it will. Integration partners file tickets, mobile apps cache the error, and monitoring treats the response as healthy because it is a valid status code. A 501 is legitimate when documented — // TODO(ISSUE-123): refunds require Stripe migration — but unjustified 501s are indistinguishable from a forgotten stub.

Either implement the handler or annotate the 501 with a specific feature reference, issue number, and target window, then return a structured error body so clients can parse the gap. Example at app/api/refunds/route.ts:

// TODO(ISSUE-123): refunds require Stripe migration — target Q2 2026
export async function DELETE() {
  return Response.json(
    { error: 'Refunds not yet supported', issue: 'ISSUE-123' },
    { status: 501 }
  )
}