fix(sync): address PR review — guard Troubleshoot during sync, narrow temp-dir fallback

- Disable the Troubleshoot Sync Advanced entry while a sync is in flight
  (matches the former Reset tile), so recovery can't race an active sync.
  The error-banner route stays open (error != syncing).
- resolveSyncTempDir now falls back to systemTemp ONLY when path_provider's
  plugin infra is absent (MissingPluginException / uninitialized test
  binding), not on any exception, so a genuine runtime failure surfaces
  instead of silently reintroducing the /tmp EPERM.

Author: ericgriffin

lib/core/services/sync/changeset_log/sync_temp_dir.dart

@@ -1,21 +1,31 @@
 import 'dart:io';
 
+import 'package:flutter/foundation.dart' show FlutterError;
+import 'package:flutter/services.dart' show MissingPluginException;
 import 'package:path_provider/path_provider.dart';
 
 /// Directory for streaming-sync temp files (base export + assembled base parts).
 ///
 /// Prefers the app-container temp dir via path_provider. A sandboxed or
 /// hardened-runtime macOS app is denied `Directory.systemTemp` (`/tmp`) ->
 /// `PathAccessException` errno 1 (issue #509), so `/tmp` must never be used in
-/// production. Falls back to `systemTemp` ONLY when path_provider is
-/// unavailable -- e.g. a plain unit test with no mocked plugin channel -- where
-/// `/tmp` is writable, so the fallback keeps such tests green without every one
-/// of them mocking path_provider. In production getTemporaryDirectory always
-/// resolves, so the fallback never runs there.
+/// production.
+///
+/// Falls back to `systemTemp` ONLY when path_provider's plugin infrastructure
+/// is absent -- a plain unit test with no mocked channel
+/// ([MissingPluginException]) or no initialized test binding at all (the
+/// [FlutterError] "Binding has not yet been initialized"). In tests `/tmp` is
+/// writable, so this keeps them green without every one mocking path_provider.
+/// Any OTHER failure (e.g. a real [PlatformException] from the native side) is
+/// a genuine runtime problem and propagates, rather than silently
+/// reintroducing the `/tmp` EPERM this fix exists to avoid. In production
+/// getTemporaryDirectory resolves normally, so no fallback runs.
 Future<Directory> resolveSyncTempDir() async {
   try {
     return await getTemporaryDirectory();
-  } catch (_) {
+  } on MissingPluginException {
+    return Directory.systemTemp;
+  } on FlutterError {
     return Directory.systemTemp;
   }
 }

lib/features/settings/presentation/pages/cloud_sync_page.dart

@@ -1183,6 +1183,11 @@ class CloudSyncPage extends ConsumerWidget {
   }
 
   Widget _buildAdvancedSection(BuildContext context, WidgetRef ref) {
+    // Recovery resets sync identity/cursors and cloud files; doing that while a
+    // sync is writing races it. Disable the entry during an active sync, as the
+    // former "Reset Sync State" tile did. A sync ERROR (the banner route) is not
+    // `syncing`, so a stuck-error user can still reach Troubleshoot.
+    final isSyncing = ref.watch(syncStateProvider).status == SyncStatus.syncing;
     return Column(
       crossAxisAlignment: CrossAxisAlignment.start,
       children: [
@@ -1199,9 +1204,14 @@ class CloudSyncPage extends ConsumerWidget {
           leading: const Icon(Icons.build),
           title: const Text('Troubleshoot Sync'),
           subtitle: const Text('Fix a stuck sync or free cloud space'),
-          onTap: () => Navigator.of(context).push(
-            MaterialPageRoute(builder: (_) => const TroubleshootSyncPage()),
-          ),
+          enabled: !isSyncing,
+          onTap: isSyncing
+              ? null
+              : () => Navigator.of(context).push(
+                  MaterialPageRoute(
+                    builder: (_) => const TroubleshootSyncPage(),
+                  ),
+                ),
         ),
         ListTile(
           leading: const Icon(Icons.logout),

test/features/settings/presentation/pages/cloud_sync_page_test.dart

@@ -1260,6 +1260,27 @@ void main() {
       expect(find.text('Repair Sync'), findsOneWidget);
     });
 
+    testWidgets('Troubleshoot Sync entry is disabled during an active sync', (
+      tester,
+    ) async {
+      // Syncing shows an indeterminate spinner that never settles.
+      await pumpPage(
+        tester,
+        syncState: const SyncState(status: SyncStatus.syncing),
+        settle: false,
+      );
+      await tester.pump();
+
+      final tile = tester.widget<ListTile>(
+        find.ancestor(
+          of: find.text('Troubleshoot Sync'),
+          matching: find.byType(ListTile),
+        ),
+      );
+      expect(tile.enabled, isFalse);
+      expect(tile.onTap, isNull);
+    });
+
     testWidgets('tapping the sync error banner opens Troubleshoot Sync', (
       tester,
     ) async {