feat: Enhance error logging for PDF preview failures and SQL timeouts

- Implemented a new method `ShapeTableNames` to gather entity and navigation table names, ensuring no blanks or duplicates are included.
- Updated `FdsMfrClient` to handle cases where schema queries return no tables, logging appropriate warnings and preventing misleading errors.
- Introduced `PdfPreviewAsync` in `IntranetController` to manage PDF preview rendering, capturing detailed logs for failures and notifying users with readable error messages.
- Added comprehensive unit tests for error logging and table name shaping to ensure robustness and correctness.
- Documented decision to persist user action failures to the `fds__admin_logdebug` table, enhancing support diagnostics.

Fuchs_DataService/FdsMfrClient.cs

@@ -92,21 +92,41 @@ public class FdsMfrClient : IDisposable
             foreach (DataRow nprw in dset.Tables("navigation_properties").Rows)
                 NavProperties[nprw.nz("name").ToLower()] = nprw.toStringDictionary();
 
-            var sqlList = new List<string> { NewDatatableSql(EntityTableName) };
-            var tableNames = new List<string> { EntityTableName };
-            foreach (DataRow ttrw in dset.Tables("tables").Rows)
+            // When mfr__getSchema itself failed (deadlock victim / timeout) there is no table name
+            // to build the TOP(0) shape queries from. Running them anyway produced a second, misleading
+            // "FROM [dbo].[]" error per sync and hid the real cause; the caller sees IsValid=false.
+            var shapeTables = ShapeTableNames(EntityTableName, dset.Tables("tables").Rows);
+            if (shapeTables.Length == 0)
             {
-                sqlList.Add(NewDatatableSql(ttrw.nz("tablename")));
-                tableNames.Add(ttrw.nz("tablename"));
+                logger?.LogWarning("DatabaseSchema for {Entity}: schema query returned no entity table (exception={Exception}); skipping table-shape load",
+                    ThisEntityName, dset.Exception);
+                _tableSet = new DataSet();
+                return;
             }
 
             _tableSet = Task.Run(async () => await getSQLDataSet_async(
-                string.Join(Environment.NewLine, sqlList),
+                string.Join(Environment.NewLine, shapeTables.Select(NewDatatableSql)),
                 FdsShared.FDSConnectionString(),
-                tablenames: tableNames.ToArray(),
+                tablenames: shapeTables,
                 options: new FdsSqlOptions(logger: logger))).Result.DataSet;
         }
 
+        /// <summary>
+        /// Entity table plus its navigation tables, without blanks: the list of tables whose
+        /// (empty) shape is loaded. Empty when the entity table itself is unknown.
+        /// </summary>
+        internal static string[] ShapeTableNames(string entityTableName, DataRowCollection navTables)
+        {
+            if (string.IsNullOrWhiteSpace(entityTableName)) return Array.Empty<string>();
+            var names = new List<string> { entityTableName };
+            foreach (DataRow row in navTables)
+            {
+                string tbl = row.nz("tablename");
+                if (!string.IsNullOrWhiteSpace(tbl) && !names.Contains(tbl)) names.Add(tbl);
+            }
+            return names.ToArray();
+        }
+
         public DataSet TgtDataset(string setId)
         {
             var dset = new DataSet();

Fuchs_DataService/Fuchs_DataService.xml

@@ -16,6 +16,12 @@
         <member name="F:fds.FdsMfr.InvoiceFileDownloadConcurrency">
             <summary>Max parallel invoice-file downloads (independent per file).</summary>
         </member>
+        <member name="M:fds.FdsMfrClient.DatabaseSchema.ShapeTableNames(System.String,System.Data.DataRowCollection)">
+            <summary>
+            Entity table plus its navigation tables, without blanks: the list of tables whose
+            (empty) shape is loaded. Empty when the entity table itself is unknown.
+            </summary>
+        </member>
         <member name="T:fds.FdsConfig">
             <summary>
             Holds the application <see cref="T:Microsoft.Extensions.Configuration.IConfiguration"/> supplied by the host (the Fuchs web app).