feat: AI 텍스트 Provider (LlmProvider) — OpenAI/Anthropic 요약·번역·교정

AI를 '키 없으면 비활성되는 부가 엣지'로 통합. 기존 변환에 무영향, 일반 변환과 충돌 없는 txt↔txt/md↔md self-edge만 노출.

- IChatClient + OpenAiChatClient/AnthropicChatClient (HttpClient 직접, SDK 의존 0)
- LlmProvider: summarize/translate/proofread/custom, ISettingsStore 키 + 환경변수(OPENAI_API_KEY/ANTHROPIC_API_KEY) 폴백
- CheckAvailabilityAsync 게이트: 키 없으면 NotReady → 그래프에서 실행 비활성
- ConvertOptions.Ai (백엔드/모델/작업/대상언어)
- 테스트 5개 (키 게이트·프롬프트 구성·그래프 엣지) — 총 34개 통과

src/Everything2Everything.Core/ConvertOptions.cs

@@ -66,6 +66,8 @@ public sealed class ConvertOptions
 
     public PdfCompressOptions PdfCompress { get; set; } = new();
 
+    public AiOptions Ai { get; set; } = new();
+
     public static ConvertOptions Quick() => new();
 }
 
@@ -140,3 +142,23 @@ public sealed class PdfCompressOptions
     /// <summary>Light(구조 최적화·무손실) | Strong(렌더 재인코딩) | Max(Ghostscript). P1은 Light만 구현.</summary>
     public string Level { get; set; } = "Light";
 }
+
+public sealed class AiOptions
+{
+    /// <summary>auto | openai | anthropic. auto는 설정된 키 중 가용한 것을 선택.</summary>
+    public string Backend { get; set; } = "auto";
+
+    /// <summary>모델 ID. null이면 백엔드별 기본값.</summary>
+    public string? Model { get; set; }
+
+    /// <summary>summarize | translate | proofread | custom.</summary>
+    public string Task { get; set; } = "summarize";
+
+    /// <summary>translate 작업의 대상 언어 (예: "영어", "일본어").</summary>
+    public string? TargetLanguage { get; set; }
+
+    /// <summary>custom 작업의 사용자 지정 지시문.</summary>
+    public string? Instruction { get; set; }
+
+    public int MaxOutputTokens { get; set; } = 2000;
+}

src/Everything2Everything.Core/Converters/ChatClients.cs

@@ -0,0 +1,90 @@
+using System.Net.Http;
+using System.Text;
+using System.Text.Json;
+
+namespace Everything2Everything.Core.Converters;
+
+/// <summary>LLM 채팅 완성 클라이언트 추상화. OpenAI/Anthropic을 동일 인터페이스로 다룬다.</summary>
+public interface IChatClient
+{
+    string Name { get; }
+    Task<string> CompleteAsync(string systemPrompt, string userPrompt, string model, int maxTokens, CancellationToken ct);
+}
+
+public sealed class OpenAiChatClient : IChatClient
+{
+    private static readonly HttpClient Http = new() { Timeout = TimeSpan.FromMinutes(3) };
+    private readonly string _apiKey;
+
+    public OpenAiChatClient(string apiKey) => _apiKey = apiKey;
+    public string Name => "OpenAI";
+
+    public async Task<string> CompleteAsync(string systemPrompt, string userPrompt, string model, int maxTokens, CancellationToken ct)
+    {
+        var body = new
+        {
+            model,
+            messages = new object[]
+            {
+                new { role = "system", content = systemPrompt },
+                new { role = "user", content = userPrompt },
+            },
+            max_tokens = maxTokens,
+        };
+        using var req = new HttpRequestMessage(HttpMethod.Post, "https://api.openai.com/v1/chat/completions");
+        req.Headers.TryAddWithoutValidation("Authorization", "Bearer " + _apiKey);
+        req.Content = new StringContent(JsonSerializer.Serialize(body), Encoding.UTF8, "application/json");
+
+        using var resp = await Http.SendAsync(req, ct).ConfigureAwait(false);
+        var json = await resp.Content.ReadAsStringAsync(ct).ConfigureAwait(false);
+        if (!resp.IsSuccessStatusCode)
+            throw new InvalidOperationException($"OpenAI API 오류 ({(int)resp.StatusCode}): {Truncate(json)}");
+
+        using var doc = JsonDocument.Parse(json);
+        return doc.RootElement.GetProperty("choices")[0].GetProperty("message").GetProperty("content").GetString() ?? "";
+    }
+
+    private static string Truncate(string s) => s.Length > 400 ? s[..400] : s;
+}
+
+public sealed class AnthropicChatClient : IChatClient
+{
+    private static readonly HttpClient Http = new() { Timeout = TimeSpan.FromMinutes(3) };
+    private readonly string _apiKey;
+
+    public AnthropicChatClient(string apiKey) => _apiKey = apiKey;
+    public string Name => "Anthropic";
+
+    public async Task<string> CompleteAsync(string systemPrompt, string userPrompt, string model, int maxTokens, CancellationToken ct)
+    {
+        var body = new
+        {
+            model,
+            max_tokens = maxTokens,
+            system = systemPrompt,
+            messages = new object[]
+            {
+                new { role = "user", content = userPrompt },
+            },
+        };
+        using var req = new HttpRequestMessage(HttpMethod.Post, "https://api.anthropic.com/v1/messages");
+        req.Headers.TryAddWithoutValidation("x-api-key", _apiKey);
+        req.Headers.TryAddWithoutValidation("anthropic-version", "2023-06-01");
+        req.Content = new StringContent(JsonSerializer.Serialize(body), Encoding.UTF8, "application/json");
+
+        using var resp = await Http.SendAsync(req, ct).ConfigureAwait(false);
+        var json = await resp.Content.ReadAsStringAsync(ct).ConfigureAwait(false);
+        if (!resp.IsSuccessStatusCode)
+            throw new InvalidOperationException($"Anthropic API 오류 ({(int)resp.StatusCode}): {Truncate(json)}");
+
+        using var doc = JsonDocument.Parse(json);
+        var content = doc.RootElement.GetProperty("content");
+        var sb = new StringBuilder();
+        foreach (var block in content.EnumerateArray())
+            if (block.TryGetProperty("text", out var text))
+                sb.Append(text.GetString());
+        return sb.ToString();
+    }
+
+    private static string Truncate(string s) => s.Length > 400 ? s[..400] : s;
+}

src/Everything2Everything.Core/Converters/LlmProvider.cs

@@ -0,0 +1,127 @@
+using Everything2Everything.Core.Providers;
+
+namespace Everything2Everything.Core.Converters;
+
+/// <summary>
+/// AI 텍스트 변환 Provider. 요약·번역·교정을 LLM(OpenAI/Anthropic)으로 수행한다.
+/// 설계 불변식: 키가 없으면 CheckAvailabilityAsync가 NotReady를 반환해 비활성되고, 기존 변환은 영향 없다.
+/// 일반 변환과 충돌하지 않도록 txt→txt / md→md self-edge(동일 포맷, 내용만 가공)만 노출한다.
+/// </summary>
+public sealed class LlmProvider : IConverterProvider
+{
+    private readonly ISettingsStore _settings;
+
+    public LlmProvider(ISettingsStore settings) => _settings = settings;
+
+    public ProviderCapability Capability { get; } = new(
+        Id: "ai",
+        DisplayName: "AI 텍스트 (요약·번역·교정)",
+        SupportedConversions: new[]
+        {
+            new ConversionPair(".txt", ".txt", LossClass.Recode),
+            new ConversionPair(".md", ".md", LossClass.Recode),
+        },
+        Status: ProviderStatus.RequiresExternal,
+        Summary: "OpenAI 또는 Anthropic API로 텍스트를 요약·번역·교정합니다 (✨AI · 종량 과금 · 네트워크 필요). API 키가 없으면 비활성됩니다.",
+        ExternalDependencies: new[]
+        {
+            new ExternalDependency(
+                Name: "OpenAI 또는 Anthropic API 키",
+                Description: "설정에서 API 키를 입력하면 활성화됩니다. 환경변수 OPENAI_API_KEY / ANTHROPIC_API_KEY 도 인식합니다.",
+                DownloadUrl: "https://platform.openai.com/api-keys",
+                IsRequired: true),
+        },
+        RoadmapNote: "이미지 캡션(비전)·메타데이터 추출(JSON)·Codex CLI OAuth는 후속 확장.");
+
+    public Task<ProviderAvailability> CheckAvailabilityAsync(CancellationToken cancellationToken = default)
+    {
+        var (client, _) = ResolveClient(new AiOptions());
+        if (client is null)
+            return Task.FromResult(ProviderAvailability.NotReady(
+                "AI API 키가 설정되지 않았습니다. 설정에서 OpenAI 또는 Anthropic 키를 입력하세요 (또는 환경변수 OPENAI_API_KEY/ANTHROPIC_API_KEY).",
+                Capability.ExternalDependencies));
+        return Task.FromResult(ProviderAvailability.Ready);
+    }
+
+    public async Task<ConvertResult> ConvertAsync(
+        string sourcePath, string outputDirectory, string outputExtension,
+        ConvertOptions options, IProgress<double>? progress, CancellationToken cancellationToken)
+    {
+        var (client, model) = ResolveClient(options.Ai);
+        if (client is null)
+            return ConvertResult.Fail(sourcePath, "AI API 키가 없습니다. 설정에서 키를 입력하세요.");
+
+        var outExt = ConversionPair.Normalize(outputExtension);
+        var baseName = Path.GetFileNameWithoutExtension(sourcePath);
+        var suffix = "_" + (options.Ai.Task ?? "ai");
+        var outPath = OutputPathHelper.ResolveOutputPath(outputDirectory, baseName, suffix, outExt, options.OnCollision);
+        if (OutputPathHelper.ShouldSkip(outPath, options.OnCollision))
+            return ConvertResult.Skip(sourcePath, "기존 파일이 있어 건너뜁니다.");
+
+        try
+        {
+            var input = await File.ReadAllTextAsync(sourcePath, cancellationToken).ConfigureAwait(false);
+            if (string.IsNullOrWhiteSpace(input))
+                return ConvertResult.Fail(sourcePath, "입력 텍스트가 비어 있습니다.");
+
+            var (system, user) = BuildPrompt(options.Ai, input);
+            progress?.Report(0.2);
+
+            var result = await client.CompleteAsync(system, user, model, options.Ai.MaxOutputTokens, cancellationToken)
+                .ConfigureAwait(false);
+            progress?.Report(0.9);
+
+            var tmp = outPath + ".tmp";
+            await File.WriteAllTextAsync(tmp, result, new System.Text.UTF8Encoding(false), cancellationToken).ConfigureAwait(false);
+            if (File.Exists(outPath)) File.Delete(outPath);
+            File.Move(tmp, outPath);
+
+            progress?.Report(1.0);
+            return ConvertResult.Ok(sourcePath, new[] { outPath });
+        }
+        catch (OperationCanceledException) { throw; }
+        catch (Exception ex)
+        {
+            return ConvertResult.Fail(sourcePath, $"AI 변환 실패: {ex.Message}", ex);
+        }
+    }
+
+    private (IChatClient? client, string model) ResolveClient(AiOptions ai)
+    {
+        var backend = (ai.Backend ?? "auto").ToLowerInvariant();
+        var openaiKey = GetKey("openai");
+        var anthropicKey = GetKey("anthropic");
+
+        if (backend == "openai")
+            return openaiKey is null ? (null, "") : (new OpenAiChatClient(openaiKey), ai.Model ?? "gpt-4o-mini");
+        if (backend == "anthropic")
+            return anthropicKey is null ? (null, "") : (new AnthropicChatClient(anthropicKey), ai.Model ?? "claude-3-5-sonnet-latest");
+
+        // auto: OpenAI 우선, 없으면 Anthropic
+        if (openaiKey is not null) return (new OpenAiChatClient(openaiKey), ai.Model ?? "gpt-4o-mini");
+        if (anthropicKey is not null) return (new AnthropicChatClient(anthropicKey), ai.Model ?? "claude-3-5-sonnet-latest");
+        return (null, "");
+    }
+
+    private string? GetKey(string provider)
+    {
+        var stored = _settings.Get($"{provider}.apikey");
+        if (!string.IsNullOrWhiteSpace(stored)) return stored;
+        var env = Environment.GetEnvironmentVariable(provider == "openai" ? "OPENAI_API_KEY" : "ANTHROPIC_API_KEY");
+        return string.IsNullOrWhiteSpace(env) ? null : env;
+    }
+
+    internal static (string system, string user) BuildPrompt(AiOptions ai, string input)
+    {
+        var task = (ai.Task ?? "summarize").ToLowerInvariant();
+        var system = task switch
+        {
+            "summarize" => "너는 문서 요약 도우미다. 입력의 핵심을 간결하고 명확하게 요약하라. 요약문만 출력하라.",
+            "translate" => $"너는 전문 번역가다. 입력을 {ai.TargetLanguage ?? "영어"}(으)로 자연스럽게 번역하라. 번역문만 출력하라.",
+            "proofread" => "너는 교정 도우미다. 입력의 오탈자·문법·어색한 표현·줄바꿈을 정리하되 원래 의미는 보존하라. 교정된 본문만 출력하라.",
+            "custom" => string.IsNullOrWhiteSpace(ai.Instruction) ? "입력 텍스트를 처리하라." : ai.Instruction!,
+            _ => "입력 텍스트를 처리하라.",
+        };
+        return (system, input);
+    }
+}

src/Everything2Everything.Core/Everything2Everything.Core.csproj

@@ -31,4 +31,8 @@
     <Using Include="System.IO" />
   </ItemGroup>
 
+  <ItemGroup>
+    <InternalsVisibleTo Include="Everything2Everything.Tests" />
+  </ItemGroup>
+
 </Project>

src/Everything2Everything.Core/Everything2EverythingBootstrap.cs

@@ -6,6 +6,7 @@ public static class Everything2EverythingBootstrap
 {
     public static ConversionEngine CreateDefault()
     {
+        var settings = new DpapiSettingsStore();
         var magick = new Converters.MagickProvider();
         var pdf = new Converters.PdfProvider();
         var providers = new IConverterProvider[]
@@ -22,6 +23,7 @@ public static class Everything2EverythingBootstrap
             new Converters.DataProvider(),
             new Converters.VectorProvider(),
             new Converters.ImageOptimProvider(),
+            new Converters.LlmProvider(settings),
         };
         return new ConversionEngine(new ProviderRegistry(providers));
     }

src/Everything2Everything.Tests/LlmProviderTests.cs

@@ -0,0 +1,68 @@
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using Everything2Everything.Core;
+using Everything2Everything.Core.Converters;
+using Xunit;
+
+namespace Everything2Everything.Tests;
+
+public class LlmProviderTests
+{
+    private sealed class FakeStore : ISettingsStore
+    {
+        private readonly Dictionary<string, string> _d = new();
+        public string? Get(string key) => _d.TryGetValue(key, out var v) ? v : null;
+        public void Set(string key, string value) => _d[key] = value;
+        public void Remove(string key) => _d.Remove(key);
+        public bool Contains(string key) => _d.ContainsKey(key);
+    }
+
+    private static bool EnvHasKey()
+        => !string.IsNullOrEmpty(Environment.GetEnvironmentVariable("OPENAI_API_KEY"))
+           || !string.IsNullOrEmpty(Environment.GetEnvironmentVariable("ANTHROPIC_API_KEY"));
+
+    [Fact]
+    public async Task NoKey_IsNotReady()
+    {
+        if (EnvHasKey()) return; // 환경변수 키가 있으면 이 단언은 건너뜀
+        var p = new LlmProvider(new FakeStore());
+        var a = await p.CheckAvailabilityAsync();
+        Assert.False(a.IsReady);
+    }
+
+    [Fact]
+    public async Task WithKey_IsReady()
+    {
+        var store = new FakeStore();
+        store.Set("openai.apikey", "sk-test-key");
+        var p = new LlmProvider(store);
+        var a = await p.CheckAvailabilityAsync();
+        Assert.True(a.IsReady);
+    }
+
+    [Fact]
+    public void BuildPrompt_Translate_IncludesTargetLanguage()
+    {
+        var (system, user) = LlmProvider.BuildPrompt(
+            new AiOptions { Task = "translate", TargetLanguage = "일본어" }, "hello");
+        Assert.Contains("일본어", system);
+        Assert.Equal("hello", user);
+    }
+
+    [Fact]
+    public void BuildPrompt_Summarize_MentionsSummary()
+    {
+        var (system, _) = LlmProvider.BuildPrompt(new AiOptions { Task = "summarize" }, "text");
+        Assert.Contains("요약", system);
+    }
+
+    [Fact]
+    public void DefaultGraph_HasAiTextSelfEdge()
+    {
+        var graph = Everything2EverythingBootstrap.CreateDefault().Providers.Graph;
+        // AI self-edge(txt→txt)가 그래프에 존재 — 키 없으면 실행 시 NotReady로 비활성되지만 엣지는 등록됨
+        Assert.NotNull(graph.FindBestPath(".txt", ".txt"));
+        Assert.NotNull(graph.FindBestPath(".md", ".md"));
+    }
+}