feat: remove LangChain.Providers.Abstractions dependency, add MEAI DI extensions

- Move non-MEAI provider interfaces (ITextToSpeechModel, ITextToImageModel,
  IImageToTextModel, ISupportsCountTokens) locally into Core/src/Providers/
- Remove LangChain.Providers.Abstractions NuGet reference from Core and Serve.OpenAI
- Add LangChain.Extensions.DependencyInjection project with MEAI service
  registration helpers (AddChatClient, AddEmbeddingGenerator, AddSpeechToTextClient)
- Update tests to use ChatMessage instead of old Message type

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: HavenDV

CLAUDE.md

@@ -48,7 +48,6 @@ src/
 │   ├── Abstractions/          # LangChain.Splitters.Abstractions (CharacterTextSplitter, etc.)
 │   └── CSharp/                # LangChain.Splitters.CSharp
 ├── Extensions/
-│   ├── DependencyInjection/   # LangChain.Extensions.DependencyInjection
 │   └── Docker/                # LangChain.Extensions.Docker
 ├── Serve/
 │   ├── Abstractions/          # LangChain.Serve.Abstractions
@@ -59,7 +58,7 @@ src/
 │   ├── Sql/                   # LangChain.Utilities.Sql
 │   └── Postgres/              # LangChain.Utilities.Postgres
 ├── Cli/                       # LangChain.Cli
-└── Providers/Abstractions/    # Local copy of provider abstractions (mirrors LangChain.Providers)
+    # Note: Non-MEAI provider interfaces (TTS, Image, ImageToText) are in Core/src/Providers/
 examples/                      # Sample projects (OpenAI, Azure, Memory, Serve, LocalRAG, etc.)
 ```
 
@@ -87,12 +86,12 @@ examples/                      # Sample projects (OpenAI, Azure, Memory, Serve,
 ### Dependencies
 
 LangChain.Core depends on:
-- `LangChain.Providers.Abstractions` (NuGet) — non-MEAI provider interfaces (ITextToSpeechModel, ITextToImageModel, IImageToTextModel) and message types (Message, MessageRole)
 - `LangChain.Databases.Abstractions` (NuGet) — message history (BaseChatMessageHistory, ChatMessageHistory)
-- `Microsoft.Extensions.AI` (NuGet) — MEAI interfaces (IChatClient, IEmbeddingGenerator, ISpeechToTextClient)
+- `Microsoft.Extensions.AI` (NuGet) — MEAI interfaces (IChatClient, IEmbeddingGenerator, ISpeechToTextClient, ChatMessage, ChatRole)
 - `Microsoft.Extensions.VectorData.Abstractions` (NuGet) — MEVA vector store abstractions (`VectorStore`, `VectorStoreCollection<TKey, TRecord>`)
 - `LangChain.DocumentLoaders.Abstractions` (project reference)
 - `LangChain.Splitters.Abstractions` (project reference)
+- Non-MEAI provider interfaces (ITextToSpeechModel, ITextToImageModel, IImageToTextModel) are defined locally in `src/Core/src/Providers/`
 
 The meta-package additionally references:
 - `tryAGI.OpenAI`, `tryAGI.Anthropic`, `Ollama` — SDK packages implementing MEAI interfaces natively

LangChain.slnx

@@ -27,6 +27,9 @@
   <Folder Name="/Extensions/">
     <File Path="src/Extensions/Directory.Build.props" />
   </Folder>
+  <Folder Name="/Extensions/DependencyInjection/">
+    <Project Path="src/Extensions/DependencyInjection/src/LangChain.Extensions.DependencyInjection.csproj" />
+  </Folder>
   <Folder Name="/Extensions/Docker/">
     <Project Path="src/Extensions/Docker/src/LangChain.Extensions.Docker.csproj" />
   </Folder>

src/Core/src/LangChain.Core.csproj

@@ -27,7 +27,6 @@
 
   <ItemGroup>
     <PackageReference Include="LangChain.Databases.Abstractions" />
-    <PackageReference Include="LangChain.Providers.Abstractions" />
     <PackageReference Include="Microsoft.Extensions.AI" />
     <PackageReference Include="Microsoft.Extensions.VectorData.Abstractions" />
   </ItemGroup>

src/Core/src/Providers/Data.cs

@@ -0,0 +1,96 @@
+namespace LangChain.Providers;
+
+/// <summary>
+/// Binary data wrapper with base64/byte[]/stream conversions.
+/// </summary>
+public class Data
+{
+    private byte[]? _bytes;
+    private string? _base64;
+
+    /// <inheritdoc cref="ToData(string)"/>
+    public static implicit operator Data(string message)
+    {
+        return ToData(message);
+    }
+
+    /// <summary>
+    /// Converts a base64 string to <see cref="Data"/>.
+    /// </summary>
+    public static Data ToData(string base64)
+    {
+        return new Data
+        {
+            _base64 = base64,
+        };
+    }
+
+    public static Data FromStream(Stream stream)
+    {
+        stream = stream ?? throw new ArgumentNullException(nameof(stream));
+
+        using var memoryStream = new MemoryStream();
+        stream.CopyTo(memoryStream);
+        memoryStream.Position = 0;
+
+        return new Data
+        {
+            _bytes = memoryStream.ToArray(),
+        };
+    }
+
+    public static Data FromBytes(byte[] bytes)
+    {
+        return new Data
+        {
+            _bytes = bytes,
+        };
+    }
+
+    public static Data FromBase64(string base64)
+    {
+        return new Data
+        {
+            _base64 = base64,
+        };
+    }
+
+    public static implicit operator byte[](Data file)
+    {
+        return file?.ToByteArray() ?? [];
+    }
+
+    public static implicit operator string(Data file)
+    {
+        return file?.ToBase64() ?? string.Empty;
+    }
+
+    public static implicit operator Stream(Data file)
+    {
+        return file?.ToStream() ?? new MemoryStream();
+    }
+
+    public string ToBase64()
+    {
+        _base64 ??= Convert.ToBase64String(_bytes ?? Array.Empty<byte>());
+
+        return _base64;
+    }
+
+    public byte[] ToByteArray()
+    {
+        _bytes ??= Convert.FromBase64String(_base64 ?? string.Empty);
+
+        return _bytes;
+    }
+
+    public MemoryStream ToStream()
+    {
+        return new MemoryStream(ToByteArray());
+    }
+
+    public override string ToString()
+    {
+        return ToBase64();
+    }
+}

src/Core/src/Providers/IModel.cs

@@ -0,0 +1,30 @@
+namespace LangChain.Providers;
+
+/// <summary>
+/// Defines common model properties.
+/// </summary>
+public interface IModel
+{
+    /// <summary>
+    /// Id of the model.
+    /// </summary>
+    public string Id { get; }
+
+    /// <summary>
+    /// Total usage of current model/provider.
+    /// </summary>
+    Usage Usage { get; }
+
+    void AddUsage(Usage usage);
+}
+
+/// <summary>
+/// Defines a model with typed settings.
+/// </summary>
+public interface IModel<TSettings> : IModel
+{
+    /// <summary>
+    /// Defines the settings for the model.
+    /// </summary>
+    public TSettings? Settings { get; set; }
+}

src/Core/src/Providers/ISupportsCountTokens.cs

@@ -0,0 +1,12 @@
+namespace LangChain.Providers;
+
+/// <summary>
+/// Interface for models that support counting tokens.
+/// </summary>
+public interface ISupportsCountTokens
+{
+    /// <summary>
+    /// Counts the number of tokens in the given text.
+    /// </summary>
+    public int CountTokens(string text);
+}

src/Core/src/Providers/ImageToText/IImageToTextModel.cs

@@ -0,0 +1,15 @@
+namespace LangChain.Providers;
+
+/// <summary>
+/// Defines a model that can generate text from images.
+/// </summary>
+public interface IImageToTextModel : IModel<ImageToTextSettings>
+{
+    /// <summary>
+    /// Generates text from the given image.
+    /// </summary>
+    public Task<ImageToTextResponse> GenerateTextFromImageAsync(
+        ImageToTextRequest request,
+        ImageToTextSettings? settings = null,
+        CancellationToken cancellationToken = default);
+}

src/Core/src/Providers/ImageToText/ImageToTextRequest.cs

@@ -0,0 +1,17 @@
+namespace LangChain.Providers;
+
+/// <summary>
+/// Image-to-text request.
+/// </summary>
+public class ImageToTextRequest
+{
+    /// <summary>
+    /// Description/prompt for the image.
+    /// </summary>
+    public string Prompt { get; init; } = string.Empty;
+
+    /// <summary>
+    /// Image to process.
+    /// </summary>
+    public required BinaryData Image { get; init; }
+}

src/Core/src/Providers/ImageToText/ImageToTextResponse.cs

@@ -0,0 +1,22 @@
+namespace LangChain.Providers;
+
+/// <summary>
+/// Image-to-text response.
+/// </summary>
+public class ImageToTextResponse
+{
+    /// <summary>
+    /// The settings used for this request.
+    /// </summary>
+    public required ImageToTextSettings UsedSettings { get; init; }
+
+    /// <summary>
+    /// Usage information.
+    /// </summary>
+    public Usage Usage { get; init; } = Usage.Empty;
+
+    /// <summary>
+    /// Generated text.
+    /// </summary>
+    public string? Text { get; set; }
+}

src/Core/src/Providers/ImageToText/ImageToTextSettings.cs

@@ -0,0 +1,36 @@
+namespace LangChain.Providers;
+
+/// <summary>
+/// Image-to-text settings.
+/// </summary>
+public class ImageToTextSettings
+{
+    public static ImageToTextSettings Default { get; } = new()
+    {
+        User = string.Empty,
+    };
+
+    /// <summary>
+    /// Unique user identifier.
+    /// </summary>
+    public string? User { get; init; }
+
+    /// <summary>
+    /// Calculate the settings to use for the request.
+    /// </summary>
+    public static ImageToTextSettings Calculate(
+        ImageToTextSettings? requestSettings,
+        ImageToTextSettings? modelSettings,
+        ImageToTextSettings? providerSettings)
+    {
+        return new ImageToTextSettings
+        {
+            User =
+                requestSettings?.User ??
+                modelSettings?.User ??
+                providerSettings?.User ??
+                Default.User ??
+                throw new InvalidOperationException("Default User is not set."),
+        };
+    }
+}