feat: dreport-service + dreport-ffi + nuget packages

Extract orchestration (font registry + render pipeline) from the Axum
backend into a standalone dreport-service crate. Backend becomes a thin
HTTP adapter on top.

Add dreport-ffi (cdylib) exposing the service through a stable C ABI
with opaque handles, byte buffers, and thread-local error reporting.

Build Dreport.Service + Dreport.AspNetCore NuGet packages under
bindings/dotnet/, packing the host RID native binary via a generated
nuspec. justfile recipes (nuget-publish, nuget-publish-all) build,
pack, and push to the Gitea NuGet registry in one shot.

Test coverage: 47 Rust + 38 C# (xUnit + WebApplicationFactory).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

bindings/dotnet/tests/Dreport.Service.Tests/Dreport.Service.Tests.csproj

@@ -0,0 +1,31 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <IsPackable>false</IsPackable>
+    <LangVersion>latest</LangVersion>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <!-- Tests run on the host RID; ensure native dylibs ship next to the test asm. -->
+    <CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
+    <PackageReference Include="xunit" Version="2.9.2" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\Dreport.Service\Dreport.Service.csproj" />
+  </ItemGroup>
+
+  <!-- Sample TTF for FontParseException tests; copied from the workspace assets dir. -->
+  <ItemGroup>
+    <None Include="..\..\..\..\dreport-service\assets\fonts\NotoSans-Regular.ttf"
+          Link="fixtures/NotoSans-Regular.ttf"
+          CopyToOutputDirectory="PreserveNewest" />
+  </ItemGroup>
+
+</Project>

bindings/dotnet/tests/Dreport.Service.Tests/LayoutEngineTests.cs

@@ -0,0 +1,236 @@
+using System.Text.Json;
+using Dreport.Service;
+using Xunit;
+
+namespace Dreport.Service.Tests;
+
+public class LayoutEngineTests
+{
+    private const string Template = """
+        {
+          "id": "csharp",
+          "name": "C# Test",
+          "page": { "width": 210, "height": 297 },
+          "fonts": ["Noto Sans"],
+          "root": {
+            "id": "root",
+            "type": "container",
+            "position": { "type": "flow" },
+            "size": { "width": { "type": "auto" }, "height": { "type": "auto" } },
+            "direction": "column",
+            "gap": 5,
+            "padding": { "top": 15, "right": 15, "bottom": 15, "left": 15 },
+            "align": "stretch",
+            "justify": "start",
+            "style": {},
+            "children": [
+              {
+                "id": "title",
+                "type": "static_text",
+                "position": { "type": "flow" },
+                "size": { "width": { "type": "auto" }, "height": { "type": "auto" } },
+                "style": { "fontSize": 14, "fontWeight": "bold" },
+                "content": "Hello from C#"
+              }
+            ]
+          }
+        }
+        """;
+    private const string Data = "{}";
+
+    private static byte[] LoadFixtureFont() =>
+        File.ReadAllBytes(Path.Combine(AppContext.BaseDirectory, "fixtures", "NotoSans-Regular.ttf"));
+
+    // ---------------------------------------------------------------------
+    // Lifecycle
+    // ---------------------------------------------------------------------
+
+    [Fact]
+    public void Construct_DefaultEngine_HasEmbeddedFonts()
+    {
+        using var engine = new LayoutEngine();
+        Assert.True(engine.FontFamilyCount >= 1);
+    }
+
+    [Fact]
+    public void CreateEmpty_StartsWithoutFonts()
+    {
+        using var engine = LayoutEngine.CreateEmpty();
+        Assert.Equal(0, engine.FontFamilyCount);
+    }
+
+    [Fact]
+    public void NativeVersion_ReturnsNonEmpty()
+    {
+        var v = LayoutEngine.NativeVersion;
+        Assert.False(string.IsNullOrEmpty(v));
+        Assert.Contains('.', v);
+    }
+
+    [Fact]
+    public void Dispose_TwiceIsSafe()
+    {
+        var engine = new LayoutEngine();
+        engine.Dispose();
+        engine.Dispose();
+    }
+
+    [Fact]
+    public void Operations_AfterDispose_Throw()
+    {
+        var engine = new LayoutEngine();
+        engine.Dispose();
+        Assert.Throws<ObjectDisposedException>(() => engine.RenderPdf(Template, Data));
+        Assert.Throws<ObjectDisposedException>(() => engine.ListFontFamilies());
+    }
+
+    // ---------------------------------------------------------------------
+    // Font registry
+    // ---------------------------------------------------------------------
+
+    [Fact]
+    public void RegisterFont_ValidBytes_IncreasesCount()
+    {
+        using var engine = LayoutEngine.CreateEmpty();
+        engine.RegisterFont(LoadFixtureFont());
+        Assert.Equal(1, engine.FontFamilyCount);
+    }
+
+    [Fact]
+    public void RegisterFont_InvalidBytes_ThrowsFontParseException()
+    {
+        using var engine = LayoutEngine.CreateEmpty();
+        var ex = Assert.Throws<FontParseException>(() =>
+            engine.RegisterFont(new byte[] { 1, 2, 3, 4 }));
+        Assert.Equal(Native.ERR_FONT_PARSE_FAILED, ex.Code);
+    }
+
+    [Fact]
+    public void RegisterFontsDirectory_NonExisting_ThrowsFontDirectoryNotFound()
+    {
+        using var engine = LayoutEngine.CreateEmpty();
+        Assert.Throws<FontDirectoryNotFoundException>(() =>
+            engine.RegisterFontsDirectory("/no/such/dreport/test/path/xyz"));
+    }
+
+    [Fact]
+    public void RegisterFontsDirectory_ValidDir_LoadsCount()
+    {
+        var fixturesDir = Path.Combine(AppContext.BaseDirectory, "fixtures");
+        Assert.True(Directory.Exists(fixturesDir));
+
+        using var engine = LayoutEngine.CreateEmpty();
+        var count = engine.RegisterFontsDirectory(fixturesDir);
+        Assert.True(count >= 1);
+    }
+
+    [Fact]
+    public void GetFontBytes_KnownVariant_ReturnsBytes()
+    {
+        using var engine = new LayoutEngine();
+        var bytes = engine.GetFontBytes("Noto Sans", 400, false);
+        Assert.NotNull(bytes);
+        Assert.True(bytes!.Length > 1000);
+    }
+
+    [Fact]
+    public void GetFontBytes_UnknownVariant_ReturnsNull()
+    {
+        using var engine = new LayoutEngine();
+        Assert.Null(engine.GetFontBytes("DoesNotExist", 400, false));
+    }
+
+    [Fact]
+    public void ListFontFamilies_ContainsNotoSans()
+    {
+        using var engine = new LayoutEngine();
+        var families = engine.ListFontFamilies();
+        Assert.Contains(families, f => f.Family.ToLowerInvariant().Contains("noto"));
+    }
+
+    // ---------------------------------------------------------------------
+    // Render pipeline
+    // ---------------------------------------------------------------------
+
+    [Fact]
+    public void ComputeLayout_ValidInputs_ReturnsLayoutJson()
+    {
+        using var engine = new LayoutEngine();
+        var json = engine.ComputeLayout(Template, Data);
+        using var doc = JsonDocument.Parse(json);
+        Assert.True(doc.RootElement.TryGetProperty("pages", out var pages));
+        Assert.Equal(JsonValueKind.Array, pages.ValueKind);
+        Assert.True(pages.GetArrayLength() >= 1);
+    }
+
+    [Fact]
+    public void ComputeLayout_InvalidTemplate_ThrowsInvalidTemplate()
+    {
+        using var engine = new LayoutEngine();
+        Assert.Throws<InvalidTemplateException>(() => engine.ComputeLayout("{not json", Data));
+    }
+
+    [Fact]
+    public void ComputeLayout_InvalidData_ThrowsInvalidData()
+    {
+        using var engine = new LayoutEngine();
+        Assert.Throws<InvalidDataException>(() => engine.ComputeLayout(Template, "{not json"));
+    }
+
+    [Fact]
+    public void RenderPdf_ValidInputs_ReturnsPdfBytes()
+    {
+        using var engine = new LayoutEngine();
+        var pdf = engine.RenderPdf(Template, Data);
+        Assert.True(pdf.Length > 100);
+        Assert.Equal((byte)'%', pdf[0]);
+        Assert.Equal((byte)'P', pdf[1]);
+        Assert.Equal((byte)'D', pdf[2]);
+        Assert.Equal((byte)'F', pdf[3]);
+    }
+
+    [Fact]
+    public void RenderPdf_InvalidTemplate_ThrowsInvalidTemplate()
+    {
+        using var engine = new LayoutEngine();
+        Assert.Throws<InvalidTemplateException>(() => engine.RenderPdf("{not json", Data));
+    }
+
+    // ---------------------------------------------------------------------
+    // Concurrency
+    // ---------------------------------------------------------------------
+
+    [Fact]
+    public void RenderPdf_Parallel_ProducesPdfs()
+    {
+        using var engine = new LayoutEngine();
+        var success = 0;
+        Parallel.For(0, 16, _ =>
+        {
+            var pdf = engine.RenderPdf(Template, Data);
+            if (pdf.Length > 100 && pdf[0] == (byte)'%')
+            {
+                Interlocked.Increment(ref success);
+            }
+        });
+        Assert.Equal(16, success);
+    }
+
+    // ---------------------------------------------------------------------
+    // Error code stability (matches Rust ServiceError::code() contract)
+    // ---------------------------------------------------------------------
+
+    [Fact]
+    public void ErrorCode_InvalidTemplate_IsMinusOne()
+    {
+        var ex = new InvalidTemplateException("x");
+        Assert.Equal(-1, ex.Code);
+    }
+
+    [Fact]
+    public void ErrorCode_FontParseFailed_IsMinusThree()
+    {
+        var ex = new FontParseException("x");
+        Assert.Equal(-3, ex.Code);
+    }
+}