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

app/MindWork AI Studio/Components/Settings/SettingsPanelEmbeddings.razor.cs

@@ -94,6 +94,7 @@ public partial class SettingsPanelEmbeddings : SettingsPanelProviderBase
             { x => x.IsEditing, true },
             { x => x.DataHost, embeddingProvider.Host },
             { x => x.DataTokenizerPath, embeddingProvider.TokenizerPath },
+            { x => x.DataTokenizerFingerprint, embeddingProvider.TokenizerFingerprint },
             { x => x.DataTokenLimit, embeddingProvider.EffectiveTokenLimit },
             { x => x.DataEmbeddingBatchSize, embeddingProvider.EffectiveEmbeddingBatchSize },
             { x => x.HFInferenceProviderId, embeddingProvider.HFInferenceProvider },

app/MindWork AI Studio/Dialogs/EmbeddingProviderDialog.razor.cs

@@ -86,6 +86,17 @@ public partial class EmbeddingProviderDialog : MSGComponentBase, ISecretId
     [Parameter]
     public string DataTokenizerPath { get; set; } = string.Empty;
 
+    /// <summary>
+    /// The fingerprint of the tokenizer this provider was stored with.
+    /// </summary>
+    /// <remarks>
+    /// Carried through the dialog untouched as long as the user leaves the tokenizer alone. Rebuilding
+    /// it from the path on every open would read a file for nothing, and an unreadable one would look
+    /// like another tokenizer and cost every data source of this provider its index.
+    /// </remarks>
+    [Parameter]
+    public string DataTokenizerFingerprint { get; set; } = string.Empty;
+
     [Parameter]
     public int DataTokenLimit { get; set; } = EmbeddingProvider.DEFAULT_TOKEN_LIMIT;
 
@@ -121,6 +132,7 @@ public partial class EmbeddingProviderDialog : MSGComponentBase, ISecretId
     private string dataEditingPreviousInstanceName = string.Empty;
     private string dataLoadingModelsIssue = string.Empty;
     private string dataFilePath = string.Empty;
+    private string dataTokenizerFingerprint = string.Empty;
     private string dataCustomTokenizerValidationIssue = string.Empty;
     private Task dataTokenizerValidationTask = Task.CompletedTask;
     private bool dataStoreWasAttempted;
@@ -176,6 +188,7 @@ public partial class EmbeddingProviderDialog : MSGComponentBase, ISecretId
             IsEnterpriseConfiguration = this.IsEnterpriseConfiguration,
             EnterpriseConfigurationPluginId = Guid.Empty,
             TokenizerPath = this.dataFilePath,
+            TokenizerFingerprint = this.dataTokenizerFingerprint,
             EmbeddingBatchSize = this.DataEmbeddingBatchSize,
             TokenLimit = this.DataTokenLimit,
             CustomIconDataUrl = this.DataCustomIconDataUrl,
@@ -201,6 +214,7 @@ public partial class EmbeddingProviderDialog : MSGComponentBase, ISecretId
         {
             this.dataEditingPreviousInstanceName = this.DataName.ToLowerInvariant();
             this.dataFilePath = this.DataTokenizerPath;
+            this.dataTokenizerFingerprint = this.DataTokenizerFingerprint;
             this.showExpertSettings = !string.IsNullOrWhiteSpace(this.DataTokenizerPath)
                                       || this.DataTokenLimit != EmbeddingProvider.DEFAULT_TOKEN_LIMIT
                                       || this.DataEmbeddingBatchSize != EmbeddingProvider.DEFAULT_EMBEDDING_BATCH_SIZE;
@@ -413,9 +427,18 @@ public partial class EmbeddingProviderDialog : MSGComponentBase, ISecretId
         this.dataTokenizerValidationTask = this.ValidateCustomTokenizer(filePath, validationRevision);
         await this.dataTokenizerValidationTask;
 
+        //
+        // The embedding signature carries the tokenizer's content, so it has to be read while we have
+        // the file the user just picked. Reading it here rather than while storing also keeps a large
+        // file off that path, where it would stall the circuit.
+        //
+        var tokenizerFingerprint = await TokenizerFingerprint.ForFileAsync(filePath);
+
         if (validationRevision != this.dataTokenizerValidationRevision)
             return;
 
+        this.dataTokenizerFingerprint = tokenizerFingerprint;
+
         if (this.dataStoreWasAttempted)
             await this.form.Validate();
         else

app/MindWork AI Studio/Settings/EmbeddingProvider.cs

@@ -23,6 +23,7 @@ public sealed record EmbeddingProvider(
     string Hostname = "http://localhost:1234",
     Host Host = Host.NONE,
     string TokenizerPath = "",
+    string TokenizerFingerprint = "",
     int EmbeddingBatchSize = 0,
     int TokenLimit = 0,
     bool AllowUserProvidedAPIKey = false,

app/MindWork AI Studio/Tools/PluginSystem/PluginConfigurationObject.cs

@@ -497,7 +497,17 @@ public sealed record PluginConfigurationObject
             TokenizerModelId.ForEmbeddingProvider(provider),
             $"embedding provider '{provider.Name}'");
 
-        return provider with { TokenizerPath = syncedTokenizerPath };
+        //
+        // The embedding signature is built from the tokenizer's content, so the fingerprint travels
+        // with the provider. An unreadable file yields nothing, and writing that would look like
+        // another tokenizer and cost every data source of this provider its index -- so in that case
+        // the previous fingerprint is kept rather than cleared.
+        //
+        var syncedTokenizerFingerprint = await TokenizerFingerprint.ForFileAsync(syncedTokenizerPath);
+        if (string.IsNullOrEmpty(syncedTokenizerFingerprint) && !string.IsNullOrWhiteSpace(syncedTokenizerPath))
+            syncedTokenizerFingerprint = provider.TokenizerFingerprint;
+
+        return provider with { TokenizerPath = syncedTokenizerPath, TokenizerFingerprint = syncedTokenizerFingerprint };
     }
 
     private static async Task<string> SyncTokenizerAsync(string configuredTokenizerPath, string pluginPath, string modelId, string logName)

app/MindWork AI Studio/Tools/Services/DataSourceEmbeddingService.Files.cs

@@ -994,6 +994,13 @@ public sealed partial class DataSourceEmbeddingService
     /// where it runs, how the text was cut for it, and the chunk metadata version — the things a
     /// vector actually depends on.
     ///
+    /// Two of them are less obvious than they look. The Hugging Face inference provider belongs to
+    /// where the model runs: the same model name served by another backend is another vector source.
+    /// And a custom tokenizer enters through its content, not through its path, because a tokenizer
+    /// is stored under the name it came with — almost always tokenizer.json — so swapping one for
+    /// another lands on the identical path, while moving the data directory changes every path
+    /// without changing a single tokenizer.
+    ///
     /// The confidence level a data source asks of a provider is deliberately not among them. It
     /// changes no vector, and it is enforced live on every request anyway: DataSourceService checks
     /// it against the participating chat providers and against the embedding provider, and this
@@ -1010,7 +1017,8 @@ public sealed partial class DataSourceEmbeddingService
             embeddingProvider.Model.Id,
             embeddingProvider.Host,
             embeddingProvider.Hostname,
-            embeddingProvider.TokenizerPath,
+            embeddingProvider.HFInferenceProvider,
+            embeddingProvider.TokenizerFingerprint,
             embeddingProvider.EffectiveTokenLimit,
             dataSource is IInternalDataSource internalDataSource ? internalDataSource.MaxChunkTokenLength : 0,
             dataSource is IInternalDataSource overlapDataSource ? overlapDataSource.ChunkOverlapTokenLength : DEFAULT_CHUNK_OVERLAP_TOKEN_LENGTH,

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;
+        }
+    }
+}

app/Tests/Tools/EmbeddingSignatureTests.cs

@@ -1,4 +1,5 @@
 using AIStudio.Provider;
+using AIStudio.Provider.HuggingFace;
 using AIStudio.Settings;
 using AIStudio.Settings.DataModel;
 using AIStudio.Tools.Services;
@@ -47,6 +48,54 @@ public sealed class EmbeddingSignatureTests
             "Another model means another vector space, so nothing stored may be kept.");
     }
 
+    [Test]
+    public void ChangingTheTokenizerContentDropsTheStoredEmbeddings()
+    {
+        var dataSource = DataSource(ConfidenceLevel.LOW);
+        var oneTokenizer = TokenizerAt("/data/tokenizers/embeddings/tokenizer.json", "AAAA");
+        var anotherTokenizer = oneTokenizer with { TokenizerFingerprint = "BBBB" };
+
+        Assert.That(
+            Signature(dataSource, anotherTokenizer),
+            Is.Not.EqualTo(Signature(dataSource, oneTokenizer)),
+            "Another tokenizer cuts the text at other places. A tokenizer is stored under the name it came with, almost always tokenizer.json, so the path alone would not notice the swap.");
+    }
+
+    [Test]
+    public void MovingTheTokenizerFileKeepsTheStoredEmbeddings()
+    {
+        var dataSource = DataSource(ConfidenceLevel.LOW);
+        var here = TokenizerAt("/data/tokenizers/embeddings/tokenizer.json", "AAAA");
+        var there = here with { TokenizerPath = "/somewhere/else/tokenizers/embeddings/tokenizer.json" };
+
+        Assert.That(
+            Signature(dataSource, there),
+            Is.EqualTo(Signature(dataSource, here)),
+            "It is the same tokenizer and only the data directory moved, so embedding everything again would buy nothing.");
+    }
+
+    [Test]
+    public void ChangingTheHuggingFaceInferenceProviderDropsTheStoredEmbeddings()
+    {
+        var dataSource = DataSource(ConfidenceLevel.LOW);
+        var oneBackend = EmbeddingProviderFor("text-embedding-3-small") with { HFInferenceProvider = HFInferenceProvider.GROQ };
+        var anotherBackend = oneBackend with { HFInferenceProvider = HFInferenceProvider.CEREBRAS };
+
+        Assert.That(
+            Signature(dataSource, anotherBackend),
+            Is.Not.EqualTo(Signature(dataSource, oneBackend)),
+            "The same model name served by another backend is another vector source.");
+    }
+
+    [Test]
+    public void TheSignatureOfAKnownConfigurationIsPinned()
+    {
+        Assert.That(
+            Signature(DataSource(ConfidenceLevel.LOW)),
+            Is.EqualTo("2|b0a4c4d2-1f3e-4f0a-8c9d-5a6b7c8d9e01|OPEN_AI|text-embedding-3-small|NONE|http://localhost:1234|NONE||8192|512|100|512|100"),
+            "Reordering or extending the signature throws away every index anybody has. This test makes that a decision somebody takes rather than something which happens on the way past.");
+    }
+
     private static string Signature(DataSourceLocalDirectory dataSource, EmbeddingProvider? embeddingProvider = null) =>
         DataSourceEmbeddingService.BuildEmbeddingSignature(
             dataSource,
@@ -67,6 +116,9 @@ public sealed class EmbeddingSignatureTests
         Path = "/tmp/test-data",
     };
 
+    private static EmbeddingProvider TokenizerAt(string tokenizerPath, string tokenizerFingerprint) =>
+        EmbeddingProviderFor("text-embedding-3-small") with { TokenizerPath = tokenizerPath, TokenizerFingerprint = tokenizerFingerprint };
+
     private static EmbeddingProvider EmbeddingProviderFor(string modelId) =>
         new(1, "b0a4c4d2-1f3e-4f0a-8c9d-5a6b7c8d9e01", "Test embeddings", LLMProviders.OPEN_AI, new(modelId, modelId));
 }