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/api/errors/error_mapper.dart

@@ -54,11 +54,61 @@ AppException? _dioToAppException(DioException error) {
   }
 }
 
+final RegExp _davException = RegExp(
+  r'<s:exception>\s*([^<]*?)\s*</s:exception>',
+);
+final RegExp _davMessage = RegExp(r'<s:message>\s*([^<]*?)\s*</s:message>');
+
+/// The Sabre DAV error body of a failed WebDAV request: the exception class
+/// (without its `Sabre\DAV\Exception\` namespace) and the server's message.
+/// The class says what actually went wrong where the status is ambiguous —
+/// MKCOL on an existing folder is a plain 405.
+({String exception, String message})? parseDavError(String body) {
+  final exception = _davException.firstMatch(body)?.group(1);
+  if (exception == null || exception.isEmpty) return null;
+  return (
+    exception: exception.split('\\').last,
+    message: _davMessage.firstMatch(body)?.group(1) ?? '',
+  );
+}
+
+AppException? _davToAppException(
+  int status,
+  ({String exception, String message}) dav,
+  String detail,
+) {
+  final userMessage = switch (dav.exception) {
+    'MethodNotAllowed' when status == 405 =>
+      'Ein Ordner oder eine Datei mit diesem Namen existiert bereits.',
+    'PreconditionFailed' =>
+      'Am Zielort existiert bereits ein Eintrag mit diesem Namen.',
+    'Conflict' => 'Der übergeordnete Ordner existiert nicht mehr.',
+    'Locked' =>
+      'Der Eintrag wird gerade bearbeitet. Bitte versuche es gleich erneut.',
+    'InsufficientStorage' =>
+      'Der verfügbare Speicherplatz reicht dafür nicht aus.',
+    _ => null,
+  };
+  if (userMessage == null) return null;
+  return ServerException(
+    statusCode: status,
+    userMessage: userMessage,
+    technicalDetails: detail,
+    allowRetry: dav.exception == 'Locked',
+  );
+}
+
 /// The nextcloud/dynamite clients throw [DynamiteApiException] on non-2xx.
 /// Its toString() dumps every response header, so the details keep only the
 /// status plus a trimmed body preview (same format as the Talk API errors).
 AppException _dynamiteToAppException(DynamiteApiException error) {
   final status = error.statusCode;
+  final dav = parseDavError(error.body);
+  if (dav != null) {
+    final detail = 'HTTP $status ${dav.exception}: ${dav.message}';
+    return _davToAppException(status, dav, detail) ??
+        exceptionForStatus(status, detail);
+  }
   final preview = previewBody(error.body);
   final detail = preview.isEmpty
       ? 'HTTP $status'