Refactor document name sanitization for consistent filename generation

- Introduced FdsDocumentNames class to centralize the logic for sanitizing document names used in downloads.
- Updated FdsMfr to utilize the new SafeFileName method for generating safe filenames.
- Enhanced documentation for FdsDocumentNames and its methods to clarify usage and purpose.
- Added global.json file to configure testing framework settings.

Fuchs_DataService/FdsMfr.cs

@@ -205,9 +205,12 @@ public class FdsMfr : IFdsMfr
             if (fl != null)
             {
                 file = fl;
-                string safeName = fln.Replace("<p>", "").Replace("</p>", "").Replace("=", "_")
-                    .Replace(">", "_").Replace("|", "_").Replace("!", "_").Replace("<", "_").Replace("/", "_");
-                return new FileInfo(Path.GetTempPath() + safeName);
+                // Same sanitiser as the regenerate-on-miss path (ADR 0025) so a stored and a
+                // regenerated document with the same DocumentName download under the same name.
+                // Fallback to the report id: an empty DocumentName used to yield the temp-dir
+                // segment ("Temp") as the download name.
+                string safeName = FdsDocumentNames.SafeFileName(fln, reportid);
+                return new FileInfo(Path.Combine(Path.GetTempPath(), safeName));
             }
         }
         return null;

Fuchs_DataService/FdsShared.cs

@@ -40,6 +40,33 @@ public static class FdsConfig
         Current["Fds:MFR_host"] ?? "";
 }
 
+/// <summary>
+/// Download-filename sanitising shared by every path that hands a document to the browser —
+/// stored documents (<see cref="FdsMfr.GetReportDoc"/>) and documents regenerated on a miss
+/// (<c>IntranetController.HandleReportDoc</c>, ADR 0025) — so both produce the same name for the
+/// same DocumentName. DocumentName is derived from the user-typed invoice title, so it can carry
+/// path separators ("Wartung 2025/26"), stray editor markup and characters Windows rejects.
+/// </summary>
+public static class FdsDocumentNames
+{
+    // '=' and '!' are legal filename characters, but the stored-document path replaced them
+    // long before the regenerate path existed; kept so unifying the two never loosens either.
+    private static readonly char[] Replaced =
+        [.. Path.GetInvalidFileNameChars(), '=', '!'];
+
+    /// <param name="documentName">Raw DocumentName (may be null, empty, or wrapped in &lt;p&gt;).</param>
+    /// <param name="fallback">Used when nothing usable remains after cleanup.</param>
+    public static string SafeFileName(string? documentName, string fallback)
+    {
+        string name = (documentName ?? "").Replace("<p>", "").Replace("</p>", "").Trim();
+        if (name.Length == 0) return fallback;
+        foreach (char c in Replaced)
+            name = name.Replace(c, '_');
+        name = name.Trim();
+        return name.Length == 0 ? fallback : name;
+    }
+}
+
 internal static class FdsShared
 {
     internal static string FDSConnectionString() => FdsConfig.FDSConnectionString();

Fuchs_DataService/Fuchs_DataService.xml

@@ -37,5 +37,18 @@
             which <c>Program.cs</c> calls once at startup before any <see cref="T:fds.FdsMfr"/> use.
             </summary>
         </member>
+        <member name="T:fds.FdsDocumentNames">
+            <summary>
+            Download-filename sanitising shared by every path that hands a document to the browser —
+            stored documents (<see cref="M:fds.FdsMfr.GetReportDoc(System.Byte[]@,System.String,System.Boolean)"/>) and documents regenerated on a miss
+            (<c>IntranetController.HandleReportDoc</c>, ADR 0025) — so both produce the same name for the
+            same DocumentName. DocumentName is derived from the user-typed invoice title, so it can carry
+            path separators ("Wartung 2025/26"), stray editor markup and characters Windows rejects.
+            </summary>
+        </member>
+        <member name="M:fds.FdsDocumentNames.SafeFileName(System.String,System.String)">
+            <param name="documentName">Raw DocumentName (may be null, empty, or wrapped in &lt;p&gt;).</param>
+            <param name="fallback">Used when nothing usable remains after cleanup.</param>
+        </member>
     </members>
 </doc>