feat(machine): open a verified Bolt Card session at tap-to-enter

Entry now spends the tap's single-use SUN once, on the card server's new
/session endpoint (aiolabs/boltcards feat/card-session-endpoint), instead
of parsing the lnurlw locally and deferring every check to Complete. The
server proves a genuine, non-replayed card and returns the wallet balance
plus the hit-keyed LUD-03 withdraw and LUD-06 pay second steps — the same
single-use bearer /scan and /pay hand out — so Complete still needs no
second tap and the ATM holds no p/c for the visit.

- electron/boltcard-session.ts: /scan → /session URL derivation, response
  parsing, 404 → 'card server does not support sessions'.
- lnurl-withdraw / lnurl-pay: the second steps are now callable on their
  own (executeWithdrawCallback, resolveInvoiceFromPayStep); the tap paths
  are unchanged and reuse them.
- IPC: lnurl:open-card-session, lnurl:withdraw-session, lnurl:pay-session.
- store: handleBoltCardEntry opens the session then authorizes the
  server-returned external_id; the payment handlers take a source (raw
  tap or session); a withheld withdraw step declines with the server's
  reason. The boltcard AccessScan no longer carries the lnurlw.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

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

@@ -1,5 +1,5 @@
 import { describe, it, expect, vi } from 'vitest'
-import { executeLnurlWithdraw, lnurlwToHttps } from './lnurl-withdraw'
+import { executeLnurlWithdraw, executeWithdrawCallback, lnurlwToHttps } from './lnurl-withdraw'
 
 const BOLT11 = 'lnbc10u1p3xyz...'
 const LNURLW =
@@ -101,3 +101,44 @@ describe('executeLnurlWithdraw', () => {
     expect(res.reason).toMatch(/could not reach the card/i)
   })
 })
+
+describe('executeWithdrawCallback (session second step, no tap)', () => {
+  const step = {
+    callback: 'https://lnbits.l484.com/boltcards/api/v1/lnurl/cb/hit1',
+    k1: 'hit1',
+    maxWithdrawable: 5_000_000,
+  }
+
+  it('hands the invoice straight to the callback with k1', async () => {
+    const f = mockFetch([{ status: 'OK' }])
+    const out = await executeWithdrawCallback(step, BOLT11, { fetchImpl: f.impl })
+    expect(out).toEqual({ ok: true })
+    expect(f.calls).toHaveLength(1)
+    expect(f.calls[0]).toContain('k1=hit1')
+    expect(f.calls[0]).toContain('pr=' + BOLT11)
+  })
+
+  it('refuses an amount above the step limit without calling out', async () => {
+    const f = mockFetch([])
+    const out = await executeWithdrawCallback(step, BOLT11, {
+      fetchImpl: f.impl,
+      amountMsat: 6_000_000,
+    })
+    expect(out).toEqual({ ok: false, reason: 'card limit is below this amount' })
+    expect(f.calls).toHaveLength(0)
+  })
+
+  it('surfaces a callback decline', async () => {
+    const f = mockFetch([{ status: 'ERROR', reason: 'Payment already claimed.' }])
+    const out = await executeWithdrawCallback(step, BOLT11, { fetchImpl: f.impl })
+    expect(out).toEqual({ ok: false, reason: 'Payment already claimed.' })
+  })
+
+  it('rejects a missing invoice', async () => {
+    const f = mockFetch([])
+    expect(await executeWithdrawCallback(step, '', { fetchImpl: f.impl })).toEqual({
+      ok: false,
+      reason: 'no invoice to charge',
+    })
+  })
+})