feat: link transit registration to boxing

lib/services/registration_linking.dart

@@ -0,0 +1,39 @@
+import 'package:flutter/material.dart';
+import 'package:pad_scanner/services/code_parser.dart';
+
+const batchPaichaMismatchMessage = '批量凑箱仅支持同排产号产品，请移除不属于同一批次的总排号';
+
+bool isTransitTarget(CodeType? locationType, String? locationCode) {
+  return locationType == CodeType.locationTransit ||
+      (locationCode?.startsWith('TRANS-') ?? false);
+}
+
+String registrationSubmitLabel({
+  required bool isTransitTarget,
+  required bool isLocked,
+  required int zongpaiCount,
+}) {
+  if (!isTransitTarget) {
+    return isLocked && zongpaiCount > 1 ? '批量上架（$zongpaiCount 条）' : '确 认 上 架';
+  }
+  return isLocked && zongpaiCount > 1 ? '批量转运并凑箱（$zongpaiCount 条）' : '转运并装箱';
+}
+
+Color registrationSubmitColor({
+  required bool canSubmit,
+  required bool isTransitTarget,
+  required Color primaryColor,
+}) {
+  if (!canSubmit) return Colors.grey.shade300;
+  return isTransitTarget ? Colors.orange : primaryColor;
+}
+
+bool allSamePaicha(Iterable<String?> paichaNos) {
+  String? first;
+  for (final paichaNo in paichaNos) {
+    if (paichaNo == null || paichaNo.isEmpty) return false;
+    first ??= paichaNo;
+    if (paichaNo != first) return false;
+  }
+  return first != null;
+}

lib/services/scanner_service.dart

@@ -9,19 +9,24 @@ class ScanResult {
 }
 
 class ScannerService {
-  static const _eventChannel =
-      EventChannel('com.example.pad_scanner/scan');
-
-  Stream<ScanResult>? _scanStream;
+  static const _eventChannel = EventChannel('com.example.pad_scanner/scan');
+  static Stream<ScanResult>? _sharedScanStream;
 
   Stream<ScanResult> get scanResults {
-    _scanStream ??= _eventChannel
+    _sharedScanStream ??= _createSharedScanStream();
+    return _sharedScanStream!;
+  }
+
+  static Stream<ScanResult> _createSharedScanStream() {
+    return _eventChannel
         .receiveBroadcastStream()
         .map((event) => event as Map)
-        .map((event) => ScanResult(
-              barcode: event['barcode'] as String? ?? '',
-              codeType: event['codeType'] as String? ?? 'UNKNOWN',
-            ));
-    return _scanStream!;
+        .map(
+          (event) => ScanResult(
+            barcode: event['barcode'] as String? ?? '',
+            codeType: event['codeType'] as String? ?? 'UNKNOWN',
+          ),
+        )
+        .asBroadcastStream();
   }
 }