Add rejection payload inspection in sync view

lib/features/sync/sync_view.dart

@@ -1,3 +1,5 @@
+import 'dart:convert';
+
 import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:relationship_saver/core/config/app_theme.dart';
@@ -17,6 +19,7 @@ class SyncView extends ConsumerStatefulWidget {
 class _SyncViewState extends ConsumerState<SyncView> {
   bool _busy = false;
   String _status = 'Ready. Local-first mode keeps app usable without sync.';
+  final Set<String> _expandedRejections = <String>{};
 
   @override
   Widget build(BuildContext context) {
@@ -185,18 +188,28 @@ class _SyncViewState extends ConsumerState<SyncView> {
                   ],
                 ),
                 const SizedBox(height: 8),
-                ...state.lastRejected.map(
-                  (MutationRejection rejection) => Padding(
+                ...state.lastRejected.map((MutationRejection rejection) {
+                  final ChangeEnvelope? matched = _findRejectedChange(
+                    state.lastRejectedChanges,
+                    rejection.clientMutationId,
+                  );
+                  final bool expanded = _expandedRejections.contains(
+                    rejection.clientMutationId,
+                  );
+                  return Padding(
                     padding: const EdgeInsets.only(bottom: 10),
                     child: _rejectionTile(
                       rejection,
-                      matched: _findRejectedChange(
-                        state.lastRejectedChanges,
-                        rejection.clientMutationId,
-                      ),
+                      matched: matched,
+                      expanded: expanded,
+                      onToggleExpanded: matched?.payload == null
+                          ? null
+                          : () => _toggleRejectionExpanded(
+                              rejection.clientMutationId,
+                            ),
                     ),
-                  ),
-                ),
+                  );
+                }),
               ],
             ),
           ),
@@ -258,6 +271,8 @@ class _SyncViewState extends ConsumerState<SyncView> {
   Widget _rejectionTile(
     MutationRejection rejection, {
     required ChangeEnvelope? matched,
+    required bool expanded,
+    required VoidCallback? onToggleExpanded,
   }) {
     return Container(
       width: double.infinity,
@@ -300,6 +315,17 @@ class _SyncViewState extends ConsumerState<SyncView> {
                     color: AppTheme.textSecondary,
                   ),
                 ),
+              if (onToggleExpanded != null)
+                IconButton(
+                  onPressed: onToggleExpanded,
+                  tooltip: expanded ? 'Hide payload' : 'Show payload',
+                  icon: Icon(
+                    expanded
+                        ? Icons.keyboard_arrow_up_rounded
+                        : Icons.keyboard_arrow_down_rounded,
+                    color: AppTheme.textSecondary,
+                  ),
+                ),
             ],
           ),
           const SizedBox(height: 6),
@@ -307,6 +333,21 @@ class _SyncViewState extends ConsumerState<SyncView> {
             rejection.message,
             style: Theme.of(context).textTheme.bodyMedium,
           ),
+          if (expanded && matched?.payload != null) ...<Widget>[
+            const SizedBox(height: 10),
+            Container(
+              width: double.infinity,
+              padding: const EdgeInsets.all(10),
+              decoration: BoxDecoration(
+                color: const Color(0xFFF3F8FB),
+                borderRadius: BorderRadius.circular(10),
+              ),
+              child: SelectableText(
+                const JsonEncoder.withIndent('  ').convert(matched!.payload),
+                style: Theme.of(context).textTheme.bodySmall,
+              ),
+            ),
+          ],
         ],
       ),
     );
@@ -435,4 +476,14 @@ class _SyncViewState extends ConsumerState<SyncView> {
       }
     }
   }
+
+  void _toggleRejectionExpanded(String clientMutationId) {
+    setState(() {
+      if (_expandedRejections.contains(clientMutationId)) {
+        _expandedRejections.remove(clientMutationId);
+      } else {
+        _expandedRejections.add(clientMutationId);
+      }
+    });
+  }
 }