Added the guided chat to the BeyondFacts Lab (#1177)

app/MindWork AI Studio/Assistants/BeyondFactsLab/BflThreadId.cs

@@ -0,0 +1,40 @@
+using System.Security.Cryptography;
+using System.Text;
+
+namespace AIStudio.Assistants.BeyondFactsLab;
+
+/// <summary>
+/// Gives each chat of the BeyondFacts Lab an ID which follows from where it lives.
+/// </summary>
+/// <remarks>
+/// The provenance store keeps what a chat received by the ID of the chat, and its cleanup at the start removes what
+/// belongs to no chat on the disk. With IDs which follow from the preparation and the step, the cleanup finds the
+/// chats of the lab from the folders alone, without reading a single chat; see ProvenanceCleanup. A chat started
+/// over keeps its ID, so what the old conversation received becomes unreferenced and goes at the next cleanup.
+/// The ID is a version 8 UUID after RFC 9562, built from a SHA-256 hash.
+/// </remarks>
+public static class BflThreadId
+{
+    /// <summary>
+    /// What sets the IDs of the lab apart from any other name-based ID.
+    /// </summary>
+    private const string NAMESPACE = "beyondfacts-lab/thread/";
+
+    /// <summary>
+    /// Gets the ID of the chat of a step.
+    /// </summary>
+    /// <param name="projectId">The ID of the preparation.</param>
+    /// <param name="step">The step.</param>
+    /// <returns>The ID, the same on every computer and in every run.</returns>
+    public static Guid Of(Guid projectId, BflStep step)
+    {
+        var name = Encoding.UTF8.GetBytes($"{NAMESPACE}{projectId:D}/{step.FolderName}");
+        Span<byte> hash = stackalloc byte[SHA256.HashSizeInBytes];
+        SHA256.HashData(name, hash);
+
+        var bytes = hash[..16];
+        bytes[6] = (byte)((bytes[6] & 0x0F) | 0x80);
+        bytes[8] = (byte)((bytes[8] & 0x3F) | 0x80);
+        return new Guid(bytes, bigEndian: true);
+    }
+}