Cache NDEF data to eliminate repeated reader commands

Previously, NDEF data was read on every 500ms poll cycle even when using
cached card detection. This caused excessive reader command traffic that
could trigger firmware bugs in readers like ACR1252 (hanging after ~14
consecutive operations).

Now the cache includes NDEF data, so detection + NDEF read happens only
once per card UID. Subsequent polls return cached data with zero reader
commands.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: AlbertMN

internal/core/card.go

@@ -33,8 +33,9 @@ type Card struct {
 }
 
 // cardDetectionCache stores card detection results keyed by UID to avoid
-// re-running expensive detection (GET_VERSION, CC reads, memory probes)
-// on every poll cycle. The cache is cleared when a card is removed.
+// re-running expensive detection (GET_VERSION, CC reads, memory probes, NDEF reads)
+// on every poll cycle. This dramatically reduces reader command traffic and prevents
+// readers like ACR1252 from becoming unresponsive due to rapid command sequences.
 var (
 	cardDetectionCache   = make(map[string]*Card)
 	cardDetectionCacheMu sync.RWMutex
@@ -119,7 +120,10 @@ func GetCardUID(readerName string) (*Card, error) {
 
 	var cardInfo *Card
 	if found {
-		// Use cached detection results - only update ATR in case it changed
+		// Use cached detection results including NDEF data.
+		// This dramatically reduces reader command traffic - we only detect once
+		// per card UID, not on every 500ms poll. Critical for readers like ACR1252
+		// that become unresponsive with rapid command sequences.
 		logging.Debug(logging.CatCard, "Using cached card detection", map[string]any{"uid": uidHex})
 		cardInfo = &Card{
 			UID:         cachedCard.UID,
@@ -129,6 +133,9 @@ func GetCardUID(readerName string) (*Card, error) {
 			ProtocolISO: cachedCard.ProtocolISO,
 			Size:        cachedCard.Size,
 			Writable:    cachedCard.Writable,
+			Data:        cachedCard.Data,
+			DataType:    cachedCard.DataType,
+			URL:         cachedCard.URL,
 		}
 	} else {
 		// No cache - run full detection
@@ -140,7 +147,10 @@ func GetCardUID(readerName string) (*Card, error) {
 		// Detect card type by reading version info (for NTAG cards)
 		detectCardType(card, cardInfo)
 
-		// Cache the detection result (excluding NDEF data which may change)
+		// Try to read NDEF data from the card
+		readNDEFData(card, cardInfo)
+
+		// Cache the detection result including NDEF data
 		cardDetectionCacheMu.Lock()
 		cardDetectionCache[uidHex] = &Card{
 			UID:         cardInfo.UID,
@@ -150,18 +160,20 @@ func GetCardUID(readerName string) (*Card, error) {
 			ProtocolISO: cardInfo.ProtocolISO,
 			Size:        cardInfo.Size,
 			Writable:    cardInfo.Writable,
+			Data:        cardInfo.Data,
+			DataType:    cardInfo.DataType,
+			URL:         cardInfo.URL,
 		}
 		cardDetectionCacheMu.Unlock()
 		logging.Debug(logging.CatCard, "Cached card detection result", map[string]any{
-			"uid":  uidHex,
-			"type": cardInfo.Type,
-			"size": cardInfo.Size,
+			"uid":      uidHex,
+			"type":     cardInfo.Type,
+			"size":     cardInfo.Size,
+			"hasNDEF":  cardInfo.Data != "",
+			"dataType": cardInfo.DataType,
 		})
 	}
 
-	// Try to read NDEF data from the card
-	readNDEFData(card, cardInfo)
-
 	return cardInfo, nil
 }