Improved exports (#993)

Co-authored-by: Thorsten Sommer <SommerEngineering@users.noreply.github.com>

app/MindWork AI Studio/Tools/MessageFile.cs

@@ -0,0 +1,14 @@
+namespace AIStudio.Tools;
+
+/// <summary>
+/// A file found in a message, ready to be written: a table the model wrote, or a code block the
+/// model marked as a format we write.
+/// </summary>
+/// <param name="Ordinal">Which table or which code block of the message this is, counting from one
+/// within its kind; the format tells the two kinds apart, see FileExportFormatExtensions.IsTabular.
+/// This is what tells two files of one kind apart even when they carry the same heading.</param>
+/// <param name="Caption">What the file is about: the heading above it, or else the first column
+/// heading of a table. Empty for a code block without a heading above it.</param>
+/// <param name="Format">The format this content is written as.</param>
+/// <param name="Content">The finished file content.</param>
+public sealed record MessageFile(int Ordinal, string Caption, FileExportFormat Format, string Content);