fixed client-reported crashes in the pdf viewer, image picker and prosemirror images, mapped webdav errors to user messages and hardened keychain, cache and push stores against io failures

lib/push/chat_thread_store.dart

@@ -1,5 +1,6 @@
 import 'dart:convert';
 
+import 'package:flutter/foundation.dart';
 import 'package:localstore/localstore.dart';
 
 /// Maximum messages kept per chat thread — enough for a messenger-style
@@ -190,8 +191,15 @@ class ChatThreadStore {
   DocumentRef _doc(String chatToken) =>
       _db.collection(_collection).doc(docIdForToken(chatToken));
 
-  Future<void> _write(String chatToken, List<ThreadMessage> messages) =>
-      _doc(chatToken).set({
+  /// Best effort: a full disk must not keep the notification from being
+  /// shown; the thread just restarts from the next push.
+  Future<void> _write(String chatToken, List<ThreadMessage> messages) async {
+    try {
+      await _doc(chatToken).set({
         'messages': [for (final m in messages) m.toJson()],
       });
+    } on Object catch (e) {
+      debugPrint('ChatThreadStore.write($chatToken) failed: $e');
+    }
+  }
 }

lib/push/nid_store.dart

@@ -1,3 +1,4 @@
+import 'package:flutter/foundation.dart';
 import 'package:localstore/localstore.dart';
 
 /// A rendered notification's bookkeeping, keyed by the Nextcloud notification
@@ -40,8 +41,15 @@ class NidStore {
 
   NidStore({Localstore? db}) : _db = db ?? Localstore.instance;
 
-  Future<void> put(NidEntry entry) =>
-      _db.collection(_collection).doc('${entry.nid}').set(entry.toJson());
+  /// Best effort: a full disk must not keep the notification itself from
+  /// being shown — only a later delete-push would then miss the mapping.
+  Future<void> put(NidEntry entry) async {
+    try {
+      await _db.collection(_collection).doc('${entry.nid}').set(entry.toJson());
+    } on Object catch (e) {
+      debugPrint('NidStore.put(${entry.nid}) failed: $e');
+    }
+  }
 
   Future<NidEntry?> get(int nid) async {
     final data = await _db.collection(_collection).doc('$nid').get();

lib/push/push_secure_storage.dart

@@ -1,4 +1,5 @@
 import 'package:flutter_secure_storage/flutter_secure_storage.dart';
+import '../storage/keychain_write.dart';
 
 /// Keychain access group shared between the Runner and the (Phase 3) iOS
 /// Notification Service Extension so the NSE can read the RSA private key,
@@ -48,7 +49,9 @@ class PushSecureStorage implements FlutterSecureStorageLike {
 
   @override
   Future<void> write({required String key, required String? value}) =>
-      pushSecureStorage.write(key: key, value: value);
+      value == null
+      ? pushSecureStorage.delete(key: key)
+      : pushSecureStorage.writeRetrying(key: key, value: value);
 
   @override
   Future<void> delete({required String key}) =>