diff --git a/docs/generators/composer.md b/docs/generators/composer.md
index 3d34ad9e..bc7ee54d 100644
--- a/docs/generators/composer.md
+++ b/docs/generators/composer.md
@@ -116,7 +116,7 @@ Main attribute for marking pipeline host types.
 |---|---|---|---|
 | `InvokeMethodName` | `string` | `"Invoke"` | Name of generated sync method |
 | `InvokeAsyncMethodName` | `string` | `"InvokeAsync"` | Name of generated async method |
-| `GenerateAsync` | `bool?` | `null` | Explicit async control; null = infer from steps |
+| `GenerateAsync` | `bool` | Inferred when omitted | Explicit async control |
 | `ForceAsync` | `bool` | `false` | Force async generation even if all steps are sync |
 | `WrapOrder` | `ComposerWrapOrder` | `OuterFirst` | Determines wrapping order |
 
diff --git a/src/PatternKit.Generators.Abstractions/Composer/ComposerAttribute.cs b/src/PatternKit.Generators.Abstractions/Composer/ComposerAttribute.cs
index 484586f0..d1a00cd2 100644
--- a/src/PatternKit.Generators.Abstractions/Composer/ComposerAttribute.cs
+++ b/src/PatternKit.Generators.Abstractions/Composer/ComposerAttribute.cs
@@ -21,11 +21,10 @@ public sealed class ComposerAttribute : Attribute
 
     /// <summary>
     /// Gets or sets whether to generate async methods.
-    /// When null (default), async generation is inferred from the presence of async steps or terminal.
-    /// Note: Nullable bool in attributes is non-standard but supported by C#. 
-    /// Set to true/false explicitly to control async generation, or leave unset for inference.
+    /// When omitted, async generation is inferred from the presence of async steps or terminal.
+    /// Set to true/false explicitly to control async generation.
     /// </summary>
-    public bool? GenerateAsync { get; set; }
+    public bool GenerateAsync { get; set; }
 
     /// <summary>
     /// Gets or sets whether to force async generation even if all steps are synchronous.
diff --git a/test/PatternKit.Generators.Tests/ComposerGeneratorTests.cs b/test/PatternKit.Generators.Tests/ComposerGeneratorTests.cs
index 369aa9f8..4ebb3c2d 100644
--- a/test/PatternKit.Generators.Tests/ComposerGeneratorTests.cs
+++ b/test/PatternKit.Generators.Tests/ComposerGeneratorTests.cs
@@ -1111,4 +1111,150 @@ private Response Terminal(in Request req)
         ScenarioExpect.Equal("PKCOM006", diagnostic.Id);
         ScenarioExpect.Contains("Step", diagnostic.GetMessage(), StringComparison.Ordinal);
     }
+
+    [Scenario("GenerateAsyncFalse WithAsyncStep ReportsDiagnostic")]
+    [Fact]
+    public void GenerateAsyncFalse_WithAsyncStep_ReportsDiagnostic()
+    {
+        var source = """
+            using System;
+            using System.Threading.Tasks;
+            using PatternKit.Generators.Composer;
+
+            public readonly record struct Request(string Path);
+            public readonly record struct Response(int Status);
+
+            [Composer(GenerateAsync = false)]
+            public partial class RequestPipeline
+            {
+                [ComposeStep(0)]
+                private ValueTask<Response> StepAsync(Request req, Func<Request, ValueTask<Response>> next)
+                    => next(req);
+
+                [ComposeTerminal]
+                private Response Terminal(in Request req) => new(200);
+            }
+            """;
+
+        var comp = RoslynTestHelpers.CreateCompilation(source, nameof(GenerateAsyncFalse_WithAsyncStep_ReportsDiagnostic));
+        var gen = new ComposerGenerator();
+        _ = RoslynTestHelpers.Run(comp, gen, out var result, out _);
+
+        var diagnostic = ScenarioExpect.Single(result.Results.SelectMany(r => r.Diagnostics));
+        ScenarioExpect.Equal("PKCOM008", diagnostic.Id);
+        ScenarioExpect.Contains("StepAsync", diagnostic.GetMessage(), StringComparison.Ordinal);
+    }
+
+    [Scenario("NamedOrderAndIgnoredStep GenerateDeterministicPipeline")]
+    [Fact]
+    public void NamedOrderAndIgnoredStep_GenerateDeterministicPipeline()
+    {
+        var source = """
+            using System;
+            using PatternKit.Generators.Composer;
+
+            public readonly record struct Request(string Path);
+            public readonly record struct Response(int Status);
+
+            [Composer]
+            public partial class RequestPipeline
+            {
+                [ComposeStep(99, Order = 2, Name = "Audit")]
+                private Response Audit(in Request req, Func<Request, Response> next) => next(req);
+
+                [ComposeStep(1)]
+                private Response Auth(in Request req, Func<Request, Response> next) => next(req);
+
+                [ComposeStep(0)]
+                [ComposeIgnore]
+                private Response Ignored(in Request req, Func<Request, Response> next) => next(req);
+
+                [ComposeTerminal]
+                private Response Terminal(in Request req) => new(200);
+            }
+            """;
+
+        var comp = RoslynTestHelpers.CreateCompilation(source, nameof(NamedOrderAndIgnoredStep_GenerateDeterministicPipeline));
+        var gen = new ComposerGenerator();
+        _ = RoslynTestHelpers.Run(comp, gen, out var result, out var updated);
+
+        ScenarioExpect.All(result.Results, r => ScenarioExpect.Empty(r.Diagnostics));
+
+        var generatedSource = result.Results.SelectMany(r => r.GeneratedSources).Single().SourceText.ToString();
+        ScenarioExpect.Contains("Audit(in arg, pipeline)", generatedSource);
+        ScenarioExpect.Contains("Auth(in arg, pipeline)", generatedSource);
+        ScenarioExpect.DoesNotContain("Ignored", generatedSource);
+
+        var emit = updated.Emit(Stream.Null);
+        ScenarioExpect.True(emit.Success, string.Join("\n", emit.Diagnostics));
+    }
+
+    [Scenario("StructAsyncTerminalWithoutCancellationToken GeneratesAsyncPipeline")]
+    [Fact]
+    public void StructAsyncTerminalWithoutCancellationToken_GeneratesAsyncPipeline()
+    {
+        var source = """
+            using System;
+            using System.Threading.Tasks;
+            using PatternKit.Generators.Composer;
+
+            public readonly record struct Request(string Path);
+            public readonly record struct Response(int Status);
+
+            [Composer]
+            public partial struct RequestPipeline
+            {
+                [ComposeStep(0)]
+                private Response Audit(in Request req, Func<Request, Response> next) => next(req);
+
+                [ComposeTerminal]
+                private ValueTask<Response> TerminalAsync(Request req)
+                    => new(new Response(200));
+            }
+            """;
+
+        var comp = RoslynTestHelpers.CreateCompilation(source, nameof(StructAsyncTerminalWithoutCancellationToken_GeneratesAsyncPipeline));
+        var gen = new ComposerGenerator();
+        _ = RoslynTestHelpers.Run(comp, gen, out var result, out var updated);
+
+        ScenarioExpect.All(result.Results, r => ScenarioExpect.Empty(r.Diagnostics));
+
+        var generatedSource = result.Results.SelectMany(r => r.GeneratedSources).Single().SourceText.ToString();
+        ScenarioExpect.Contains("terminalFunc", generatedSource);
+        ScenarioExpect.Contains("self.TerminalAsync(arg)", generatedSource);
+
+        var emit = updated.Emit(Stream.Null);
+        ScenarioExpect.True(emit.Success, string.Join("\n", emit.Diagnostics));
+    }
+
+    [Scenario("InvalidStep WithFunctionPointerNext ReportsDiagnostic")]
+    [Fact]
+    public void InvalidStep_WithFunctionPointerNext_ReportsDiagnostic()
+    {
+        var source = """
+            using PatternKit.Generators.Composer;
+
+            public readonly record struct Request(string Path);
+            public readonly record struct Response(int Status);
+
+            [Composer]
+            public partial class RequestPipeline
+            {
+                [ComposeStep(0)]
+                private unsafe Response Step(in Request req, delegate*<Request, Response> next)
+                    => new(200);
+
+                [ComposeTerminal]
+                private Response Terminal(in Request req) => new(200);
+            }
+            """;
+
+        var comp = RoslynTestHelpers.CreateCompilation(source, nameof(InvalidStep_WithFunctionPointerNext_ReportsDiagnostic));
+        var gen = new ComposerGenerator();
+        _ = RoslynTestHelpers.Run(comp, gen, out var result, out _);
+
+        var diagnostic = ScenarioExpect.Single(result.Results.SelectMany(r => r.Diagnostics));
+        ScenarioExpect.Equal("PKCOM006", diagnostic.Id);
+        ScenarioExpect.Contains("Step", diagnostic.GetMessage(), StringComparison.Ordinal);
+    }
 }