Add use_pipeline step type for pipeline composition

.github/workflows/ci.yml

@@ -16,8 +16,7 @@ jobs:
       - name: Setup .NET
         uses: actions/setup-dotnet@v4
         with:
-          dotnet-version: 10.0.x
-          dotnet-quality: preview
+          dotnet-version: 10.0.103
 
       - name: Restore dependencies
         run: dotnet restore

.gitignore

@@ -118,6 +118,8 @@ docker-compose.override.yml
 publish/
 out/
 artifacts/
+*.pubxml
+*.pubxml.user
 
 ##############################
 # Coverage tools

CodeGenesis.Engine.Tests/Config/PipelineConfigLoaderTests.cs

@@ -259,6 +259,93 @@ public void LoadFromFile_ParallelMissingBranches_ThrowsInvalidOperation()
         }
     }
 
+    [Fact]
+    public void LoadFromFile_UsePipelineStep_ParsesCorrectly()
+    {
+        var yaml = """
+            pipeline:
+              name: Composition Test
+            steps:
+              - name: Run child
+                use_pipeline: ./child.yml
+                inputs:
+                  source: "some value"
+                output_key: child_result
+            """;
+
+        var path = Path.Combine(Path.GetTempPath(), $"test-{Guid.NewGuid()}.yaml");
+        File.WriteAllText(path, yaml);
+        try
+        {
+            var config = PipelineConfigLoader.LoadFromFile(path);
+
+            config.Steps.Should().HaveCount(1);
+            config.Steps[0].IsUsePipeline.Should().BeTrue();
+            config.Steps[0].IsSimpleStep.Should().BeFalse();
+            config.Steps[0].Name.Should().Be("Run child");
+            config.Steps[0].UsePipeline.Should().Be("./child.yml");
+            config.Steps[0].Inputs.Should().ContainKey("source");
+            config.Steps[0].Inputs!["source"].Should().Be("some value");
+            config.Steps[0].OutputKey.Should().Be("child_result");
+        }
+        finally
+        {
+            File.Delete(path);
+        }
+    }
+
+    [Fact]
+    public void LoadFromFile_UsePipelineMissingName_ThrowsInvalidOperation()
+    {
+        var yaml = """
+            pipeline:
+              name: Bad
+            steps:
+              - use_pipeline: ./child.yml
+            """;
+
+        var path = Path.Combine(Path.GetTempPath(), $"test-{Guid.NewGuid()}.yaml");
+        File.WriteAllText(path, yaml);
+        try
+        {
+            var act = () => PipelineConfigLoader.LoadFromFile(path);
+
+            act.Should().Throw<InvalidOperationException>()
+                .WithMessage("*missing a 'name'*");
+        }
+        finally
+        {
+            File.Delete(path);
+        }
+    }
+
+    [Fact]
+    public void LoadFromFile_UsePipelineWithOptional_ParsesCorrectly()
+    {
+        var yaml = """
+            pipeline:
+              name: Optional Test
+            steps:
+              - name: Optional child
+                use_pipeline: ./child.yml
+                optional: true
+            """;
+
+        var path = Path.Combine(Path.GetTempPath(), $"test-{Guid.NewGuid()}.yaml");
+        File.WriteAllText(path, yaml);
+        try
+        {
+            var config = PipelineConfigLoader.LoadFromFile(path);
+
+            config.Steps[0].IsUsePipeline.Should().BeTrue();
+            config.Steps[0].Optional.Should().BeTrue();
+        }
+        finally
+        {
+            File.Delete(path);
+        }
+    }
+
     [Fact]
     public void LoadFromFile_WithInputsAndOutputs_ParsesCorrectly()
     {

CodeGenesis.Engine.Tests/Config/StepEntryTests.cs

@@ -65,6 +65,41 @@ public void IsApproval_WithConfig_ReturnsTrue()
         entry.IsSimpleStep.Should().BeFalse();
     }
 
+    [Fact]
+    public void IsUsePipeline_WithUsePipeline_ReturnsTrue()
+    {
+        var entry = new StepEntry
+        {
+            Name = "sub",
+            UsePipeline = "./child.yml"
+        };
+
+        entry.IsUsePipeline.Should().BeTrue();
+        entry.IsSimpleStep.Should().BeFalse();
+        entry.IsForeach.Should().BeFalse();
+        entry.IsParallel.Should().BeFalse();
+    }
+
+    [Fact]
+    public void IsUsePipeline_WithoutUsePipeline_ReturnsFalse()
+    {
+        var entry = new StepEntry { Name = "step1", Prompt = "do something" };
+
+        entry.IsUsePipeline.Should().BeFalse();
+    }
+
+    [Fact]
+    public void IsSimpleStep_WithUsePipeline_ReturnsFalse()
+    {
+        var entry = new StepEntry
+        {
+            Name = "sub",
+            UsePipeline = "./child.yml"
+        };
+
+        entry.IsSimpleStep.Should().BeFalse();
+    }
+
     [Fact]
     public void IsSimpleStep_NullNameNoComposite_ReturnsFalse()
     {