fix(machine): cooldown after failed NFC read to prevent reader wedge

Hammering a flaky CCID reader with rapid re-reads wedges it into a
present↔empty storm (only a USB replug clears it). After a failed read,
ignore card re-detections for 1.5s; successful reads don't cool down.

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

apps/machine/electron/nfc-service.ts

@@ -155,22 +155,28 @@ export async function startNfcReader(
     r.autoProcessing = false
     onStatus({ state: 'ready', reader: name })
 
+    // Cooldown after a failed read: these cheap CCID readers can get wedged into
+    // a present↔empty storm when hammered, so ignore re-detections for a beat
+    // after a failure. Successful reads don't cool down.
+    let cooldownUntil = 0
     r.on('card', async () => {
+      if (Date.now() < cooldownUntil) return
       onStatus({ state: 'reading', reader: name })
-      // Single attempt: hammering a flaky RF link with retries wedges these
+      // Single attempt: retrying hammers a flaky RF link. A read is a few APDU
-      // cheap CCID readers. A read is a few APDU round-trips; if the card
+      // round-trips; if the card shifts mid-read the transmit fails and the
-      // shifts mid-read the transmit fails and the user simply re-taps.
+      // user simply re-taps.
       try {
         const lnurlw = await readNdefLnurlw((apdu, maxLen) => r.transmit(apdu, maxLen))
         if (lnurlw) {
           onCard(lnurlw)
-        } else {
+          return
-          onStatus({ state: 'error', reader: name, message: 'not a Bolt Card' })
         }
+        onStatus({ state: 'error', reader: name, message: 'not a Bolt Card' })
       } catch (e) {
         onStatus({ state: 'error', reader: name, message: 'card read failed — hold steady & retap' })
         void e
       }
+      cooldownUntil = Date.now() + 1500
     })
     r.on('card.off', () => onStatus({ state: 'card-removed', reader: name }))
     r.on('error', (err: unknown) =>