feat(machine): LNURL-withdraw executor for Bolt Card cash-out (LUD-03)

First, hardware-independent piece of Bolt Card tap-to-pay on the cash-out
flow. When a customer taps a Bolt Card, the ATM (which already has its
cash-out BOLT11) becomes the LNURL-*withdrawing* party: GET the card's
lnurlw voucher → GET callback?k1=…&pr=<invoice> so the card's wallet pays
the invoice. Settlement is still observed via the existing invoice watcher
(a returned ok=true means "card accepted the pull", not "cash dispensed").

- electron/lnurl-withdraw.ts: executeLnurlWithdraw() + lnurlwToHttps().
  Runs in the main process (Node fetch) to avoid renderer CORS, since LNURL
  endpoints send no CORS headers. Fully injectable fetch for testing.
- electron/lnurl-withdraw.test.ts: 12 tests (scheme mapping, two-step happy
  path passing k1+pr, ERROR surfacing, non-withdraw tag, amount-over-limit
  short-circuit, callback decline, network failure).
- IPC `lnurl:withdraw` (main) + preload + electron.d.ts.

Next: pcscd + an nfc-pcsc reader driver (reads the NTAG424 NDEF lnurlw),
then wire the tap into the cashOut displayingInvoice state + "tap or scan" UI.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/machine/electron/lnurl-withdraw.test.ts

@@ -0,0 +1,103 @@
+import { describe, it, expect, vi } from 'vitest'
+import { executeLnurlWithdraw, lnurlwToHttps } from './lnurl-withdraw'
+
+const BOLT11 = 'lnbc10u1p3xyz...'
+const LNURLW =
+  'lnurlw://lnbits.l484.com/boltcards/api/v1/scan/abc123?p=DEADBEEFDEADBEEFDEADBEEFDEADBEEF&c=1122334455667788'
+
+/** Build a mock fetch that returns the given JSON bodies per call, in order. */
+function mockFetch(bodies: unknown[]) {
+  const calls: string[] = []
+  const impl = vi.fn(async (url: string | URL) => {
+    calls.push(url.toString())
+    const body = bodies[calls.length - 1]
+    return { json: async () => body } as Response
+  })
+  return { impl: impl as unknown as typeof fetch, calls }
+}
+
+describe('lnurlwToHttps', () => {
+  it('maps lnurlw:// and lnurl:// to https://', () => {
+    expect(lnurlwToHttps('lnurlw://host/p?x=1')).toBe('https://host/p?x=1')
+    expect(lnurlwToHttps('lnurl://host/p')).toBe('https://host/p')
+  })
+  it('strips a lightning: prefix', () => {
+    expect(lnurlwToHttps('lightning:lnurlw://host/p')).toBe('https://host/p')
+  })
+  it('passes https:// through and trims', () => {
+    expect(lnurlwToHttps('  https://host/p  ')).toBe('https://host/p')
+  })
+  it('rejects http://, bech32 lnurl1…, and empty', () => {
+    expect(lnurlwToHttps('http://host/p')).toBeNull()
+    expect(lnurlwToHttps('LNURL1DP68GURN8GHJ7')).toBeNull()
+    expect(lnurlwToHttps('')).toBeNull()
+  })
+})
+
+describe('executeLnurlWithdraw', () => {
+  const withdrawReq = {
+    tag: 'withdrawRequest',
+    callback: 'https://lnbits.l484.com/boltcards/api/v1/scan/cb',
+    k1: 'K1TOKEN',
+    minWithdrawable: 1000,
+    maxWithdrawable: 5_000_000,
+  }
+
+  it('completes the two-step withdraw and passes k1 + pr to the callback', async () => {
+    const { impl, calls } = mockFetch([withdrawReq, { status: 'OK' }])
+    const res = await executeLnurlWithdraw(LNURLW, BOLT11, { fetchImpl: impl })
+    expect(res).toEqual({ ok: true })
+    // First call = the lnurlw as https; second = callback with k1 + pr.
+    expect(calls[0]).toContain('https://lnbits.l484.com/boltcards/api/v1/scan/abc123')
+    expect(calls[1]).toContain('k1=K1TOKEN')
+    expect(calls[1]).toContain(`pr=${encodeURIComponent(BOLT11)}`)
+  })
+
+  it('rejects a non-lnurlw tag', async () => {
+    const { impl } = mockFetch([])
+    const res = await executeLnurlWithdraw('http://nope', BOLT11, { fetchImpl: impl })
+    expect(res.ok).toBe(false)
+    expect(res.reason).toMatch(/not a valid Bolt Card/i)
+  })
+
+  it('rejects when there is no invoice', async () => {
+    const { impl } = mockFetch([])
+    const res = await executeLnurlWithdraw(LNURLW, '', { fetchImpl: impl })
+    expect(res).toMatchObject({ ok: false, reason: 'no invoice to charge' })
+  })
+
+  it('surfaces an ERROR from the withdraw request', async () => {
+    const { impl } = mockFetch([{ status: 'ERROR', reason: 'spent today limit' }])
+    const res = await executeLnurlWithdraw(LNURLW, BOLT11, { fetchImpl: impl })
+    expect(res).toMatchObject({ ok: false, reason: 'spent today limit' })
+  })
+
+  it('rejects a response that is not a withdrawRequest', async () => {
+    const { impl } = mockFetch([{ tag: 'payRequest', callback: 'x' }])
+    const res = await executeLnurlWithdraw(LNURLW, BOLT11, { fetchImpl: impl })
+    expect(res).toMatchObject({ ok: false })
+    expect(res.reason).toMatch(/withdraw voucher/i)
+  })
+
+  it('rejects (without calling the callback) when the amount exceeds the card limit', async () => {
+    const { impl, calls } = mockFetch([{ ...withdrawReq, maxWithdrawable: 2000 }])
+    const res = await executeLnurlWithdraw(LNURLW, BOLT11, { fetchImpl: impl, amountMsat: 5000 })
+    expect(res).toMatchObject({ ok: false, reason: 'card limit is below this amount' })
+    expect(calls).toHaveLength(1) // callback never hit
+  })
+
+  it('surfaces an ERROR from the callback (card declined)', async () => {
+    const { impl } = mockFetch([withdrawReq, { status: 'ERROR', reason: 'insufficient funds' }])
+    const res = await executeLnurlWithdraw(LNURLW, BOLT11, { fetchImpl: impl })
+    expect(res).toMatchObject({ ok: false, reason: 'insufficient funds' })
+  })
+
+  it('handles a network failure gracefully', async () => {
+    const impl = vi.fn(async () => {
+      throw new Error('ECONNREFUSED')
+    }) as unknown as typeof fetch
+    const res = await executeLnurlWithdraw(LNURLW, BOLT11, { fetchImpl: impl })
+    expect(res.ok).toBe(false)
+    expect(res.reason).toMatch(/could not reach the card/i)
+  })
+})

apps/machine/electron/lnurl-withdraw.ts

@@ -0,0 +1,127 @@
+/**
+ * LNURL-withdraw executor (LUD-03) — the ATM as the *withdrawing* party.
+ *
+ * Bolt Card tap-to-pay for the cash-out flow: a Bolt Card presents an
+ * `lnurlw://…?p=…&c=…` voucher (NTAG424 SUN — fresh p/c per tap). The ATM has
+ * already generated its cash-out BOLT11; here it asks the card's wallet to pay
+ * that invoice:
+ *   1. GET the lnurlw URL → a `withdrawRequest` (callback, k1, max/min).
+ *   2. GET `callback?k1=…&pr=<our bolt11>` → the card's wallet pays it.
+ * Settlement itself is observed elsewhere (the existing invoice watcher over
+ * nostr), so a returned `{ ok: true }` means "the card accepted the pull", not
+ * "cash dispensed" — the state machine still waits for PAYMENT_RECEIVED.
+ *
+ * Runs in the MAIN process (Node fetch) to avoid renderer CORS: LNURL
+ * endpoints don't send CORS headers, so a renderer fetch to the card's host
+ * would be blocked.
+ */
+
+export interface LnurlWithdrawResult {
+  ok: boolean
+  /** Human-readable reason when ok is false (safe to surface on-screen). */
+  reason?: string
+}
+
+/** LUD-03 withdrawRequest (subset we consume) + LUD-06 error shape. */
+interface WithdrawRequest {
+  tag?: string
+  callback?: string
+  k1?: string
+  minWithdrawable?: number
+  maxWithdrawable?: number
+  defaultDescription?: string
+  status?: string
+  reason?: string
+}
+
+type FetchLike = typeof fetch
+
+export interface ExecuteLnurlWithdrawOptions {
+  /** Injected for tests; defaults to global fetch. */
+  fetchImpl?: FetchLike
+  /**
+   * Our invoice amount in millisats. When set, we reject early if it exceeds
+   * the voucher's maxWithdrawable (defensive; the callback would reject anyway).
+   */
+  amountMsat?: number
+  /** Per-request timeout (default 15s). */
+  timeoutMs?: number
+}
+
+/**
+ * Normalize a Bolt Card / LNURL-withdraw pointer to an https URL.
+ * Bolt Cards emit `lnurlw://host/path?query`; we also accept `lnurl://` and a
+ * bare `https://`. Bech32 `LNURL1…` is intentionally unsupported (Bolt Cards
+ * never use it) and rejected with a clear reason.
+ */
+export function lnurlwToHttps(raw: string): string | null {
+  let s = raw.trim()
+  if (!s) return null
+  if (s.toLowerCase().startsWith('lightning:')) s = s.slice('lightning:'.length)
+  const lower = s.toLowerCase()
+  if (lower.startsWith('lnurlw://')) return 'https://' + s.slice('lnurlw://'.length)
+  if (lower.startsWith('lnurl://')) return 'https://' + s.slice('lnurl://'.length)
+  if (lower.startsWith('https://')) return s
+  // Reject http:// (must be TLS) and bech32 lnurl1… (not a Bolt Card).
+  return null
+}
+
+function appendQuery(url: string, params: Record<string, string>): string {
+  const u = new URL(url)
+  for (const [k, v] of Object.entries(params)) u.searchParams.set(k, v)
+  return u.toString()
+}
+
+function errMsg(e: unknown): string {
+  if (e instanceof Error) return e.name === 'TimeoutError' || e.name === 'AbortError' ? 'timed out' : e.message
+  return String(e)
+}
+
+export async function executeLnurlWithdraw(
+  lnurlw: string,
+  bolt11: string,
+  opts: ExecuteLnurlWithdrawOptions = {}
+): Promise<LnurlWithdrawResult> {
+  const doFetch = opts.fetchImpl ?? fetch
+  const timeoutMs = opts.timeoutMs ?? 15_000
+
+  const paramsUrl = lnurlwToHttps(lnurlw)
+  if (!paramsUrl) return { ok: false, reason: 'not a valid Bolt Card (lnurlw) tag' }
+  if (!bolt11 || !/^ln[a-z0-9]/i.test(bolt11.trim())) {
+    return { ok: false, reason: 'no invoice to charge' }
+  }
+
+  // 1) Fetch the withdraw request.
+  let params: WithdrawRequest
+  try {
+    const res = await doFetch(paramsUrl, { signal: AbortSignal.timeout(timeoutMs) })
+    params = (await res.json()) as WithdrawRequest
+  } catch (e) {
+    return { ok: false, reason: `could not reach the card: ${errMsg(e)}` }
+  }
+  if (params.status === 'ERROR') {
+    return { ok: false, reason: params.reason || 'card rejected the tap' }
+  }
+  if (params.tag !== 'withdrawRequest' || !params.callback || !params.k1) {
+    return { ok: false, reason: 'card did not return a withdraw voucher' }
+  }
+  if (
+    opts.amountMsat != null &&
+    typeof params.maxWithdrawable === 'number' &&
+    opts.amountMsat > params.maxWithdrawable
+  ) {
+    return { ok: false, reason: 'card limit is below this amount' }
+  }
+
+  // 2) Hand our invoice to the callback — the card's wallet pays it.
+  const cbUrl = appendQuery(params.callback, { k1: params.k1, pr: bolt11.trim() })
+  let cb: { status?: string; reason?: string }
+  try {
+    const res = await doFetch(cbUrl, { signal: AbortSignal.timeout(timeoutMs) })
+    cb = (await res.json()) as { status?: string; reason?: string }
+  } catch (e) {
+    return { ok: false, reason: `card payment failed: ${errMsg(e)}` }
+  }
+  if (cb.status === 'OK') return { ok: true }
+  return { ok: false, reason: cb.reason || 'card declined the payment' }
+}

apps/machine/electron/main.ts

@@ -42,6 +42,7 @@ import {
   type StoredBunkerBinding,
 } from './state-store.js'
 import { initializeHal, type HalInstance } from './hal-service.js'
+import { executeLnurlWithdraw } from './lnurl-withdraw.js'
 
 // ESM equivalent of __dirname
 const __filename = fileURLToPath(import.meta.url)
@@ -415,6 +416,20 @@ ipcMain.handle('app:recover', (): void => {
   reloadRenderer()
 })
 
+// Bolt Card cash-out: pull payment for the current invoice from a tapped card
+// via LNURL-withdraw. Runs in the main process (Node fetch) to dodge renderer
+// CORS. Returns once the card accepts; settlement arrives via the invoice
+// watcher. See lnurl-withdraw.ts.
+ipcMain.handle(
+  'lnurl:withdraw',
+  async (
+    _event,
+    args: { lnurlw: string; bolt11: string; amountMsat?: number }
+  ): Promise<{ ok: boolean; reason?: string }> => {
+    return executeLnurlWithdraw(args.lnurlw, args.bolt11, { amountMsat: args.amountMsat })
+  }
+)
+
 // State persistence IPC handlers
 ipcMain.handle('state:load-cassettes', () => loadCassettes())
 ipcMain.handle('state:set-cassettes', (_event, cassettes) => setCassettes(cassettes))

apps/machine/electron/preload.ts

@@ -127,6 +127,13 @@ contextBridge.exposeInMainWorld('electronAPI', {
   // Reload the renderer to re-attempt initialization (connectivity recovery).
   recoverApp: (): Promise<void> => ipcRenderer.invoke('app:recover'),
 
+  // Bolt Card cash-out: pull payment for the current invoice from a tapped card.
+  lnurlWithdraw: (args: {
+    lnurlw: string
+    bolt11: string
+    amountMsat?: number
+  }): Promise<{ ok: boolean; reason?: string }> => ipcRenderer.invoke('lnurl:withdraw', args),
+
   applyOperatorCassettesConfig: (
     payload: {
       positions: Record<string, { denomination: number; count: number }>
@@ -246,6 +253,11 @@ declare global {
       saveSpireSeed: (seed: string) => Promise<void>
       relaunchApp: () => Promise<void>
       recoverApp: () => Promise<void>
+      lnurlWithdraw: (args: {
+        lnurlw: string
+        bolt11: string
+        amountMsat?: number
+      }) => Promise<{ ok: boolean; reason?: string }>
       applyOperatorCassettesConfig: (
         payload: { positions: Record<string, { denomination: number; count: number }> },
         eventCreatedAt: number