Tie the embedding signature to the tokenizer content instead of its path

app/MindWork AI Studio/Tools/TokenizerFingerprint.cs

@@ -0,0 +1,46 @@
+using System.Security.Cryptography;
+
+namespace AIStudio.Tools;
+
+/// <summary>
+/// Identifies a tokenizer by what is inside its file, not by where the file lies.
+/// </summary>
+/// <remarks>
+/// The embedding signature asks this to decide whether stored vectors still belong to the current
+/// configuration, and the path cannot answer it. A tokenizer is stored below the data directory under
+/// the model it belongs to, keeping the name it came with -- and the usual name for one is
+/// tokenizer.json. Picking a different tokenizer with that name lands on the identical path, so the
+/// index would be kept although the chunk boundaries moved. The other way round, moving the data
+/// directory changes every path without changing a single tokenizer.
+/// </remarks>
+public static class TokenizerFingerprint
+{
+    /// <summary>
+    /// Reads a tokenizer file and returns a fingerprint of its content.
+    /// </summary>
+    /// <param name="tokenizerPath">The tokenizer file to read. May be empty when no tokenizer is set.</param>
+    /// <param name="token">The cancellation token.</param>
+    /// <returns>The fingerprint, or an empty string when there is no readable file.</returns>
+    public static async Task<string> ForFileAsync(string tokenizerPath, CancellationToken token = default)
+    {
+        if (string.IsNullOrWhiteSpace(tokenizerPath))
+            return string.Empty;
+
+        try
+        {
+            await using var stream = File.OpenRead(tokenizerPath);
+            return Convert.ToHexString(await SHA256.HashDataAsync(stream, token));
+        }
+        catch
+        {
+            //
+            // An unreadable tokenizer is not this method's problem to report: the dialog validates the
+            // file before it ever gets here, and an indexing run says so again when it cannot tokenize
+            // anything. Whoever stores a provider has to decide what an empty answer means for them,
+            // because writing it into the settings would look like another tokenizer and throw the
+            // stored vectors away.
+            //
+            return string.Empty;
+        }
+    }
+}