diff --git a/src/PatternKit.Generators/ComposerGenerator.cs b/src/PatternKit.Generators/ComposerGenerator.cs
index 9520b9a9..374753e4 100644
--- a/src/PatternKit.Generators/ComposerGenerator.cs
+++ b/src/PatternKit.Generators/ComposerGenerator.cs
@@ -371,7 +371,7 @@ private bool ValidateStepSignature(StepInfo step, SourceProductionContext contex
 
         // Validate it's actually System.Func by checking namespace and name
         var fullName = nextType.ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat);
-        if (!fullName.StartsWith("global::System.Func<"))
+        if (!fullName.StartsWith("global::System.Func<", StringComparison.Ordinal))
         {
             context.ReportDiagnostic(Diagnostic.Create(
                 InvalidStepSignatureDescriptor,
@@ -743,9 +743,9 @@ private bool IsAsyncMethod(IMethodSymbol method)
 
         var fullName = namedType.ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat);
         return fullName == "global::System.Threading.Tasks.Task" ||
-               fullName.StartsWith("global::System.Threading.Tasks.Task<") ||
+               fullName.StartsWith("global::System.Threading.Tasks.Task<", StringComparison.Ordinal) ||
                fullName == "global::System.Threading.Tasks.ValueTask" ||
-               fullName.StartsWith("global::System.Threading.Tasks.ValueTask<");
+               fullName.StartsWith("global::System.Threading.Tasks.ValueTask<", StringComparison.Ordinal);
     }
 
     private bool IsPartial(SyntaxNode node)
diff --git a/src/PatternKit.Generators/DecoratorGenerator.cs b/src/PatternKit.Generators/DecoratorGenerator.cs
index ceba9a22..fa6b6afb 100644
--- a/src/PatternKit.Generators/DecoratorGenerator.cs
+++ b/src/PatternKit.Generators/DecoratorGenerator.cs
@@ -200,7 +200,7 @@ private DecoratorConfig ParseDecoratorConfig(AttributeData attribute, INamedType
 
         // Determine default base type name
         var baseName = contractSymbol.Name;
-        if (baseName.StartsWith("I") && baseName.Length > 1 && char.IsUpper(baseName[1]))
+        if (baseName.StartsWith("I", StringComparison.Ordinal) && baseName.Length > 1 && char.IsUpper(baseName[1]))
         {
             // Interface with I prefix: IStorage -> StorageDecoratorBase
             baseName = baseName.Substring(1);
@@ -596,8 +596,8 @@ private static bool IsAsyncMethod(IMethodSymbol method)
         var returnType = method.ReturnType;
         var typeName = returnType.ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat);
 
-        return typeName.StartsWith("global::System.Threading.Tasks.Task") ||
-               typeName.StartsWith("global::System.Threading.Tasks.ValueTask");
+        return typeName.StartsWith("global::System.Threading.Tasks.Task", StringComparison.Ordinal) ||
+               typeName.StartsWith("global::System.Threading.Tasks.ValueTask", StringComparison.Ordinal);
     }
 
     private static bool CanTypeAcceptNull(ITypeSymbol type)
diff --git a/src/PatternKit.Generators/FacadeGenerator.cs b/src/PatternKit.Generators/FacadeGenerator.cs
index 76ec8bc8..36795906 100644
--- a/src/PatternKit.Generators/FacadeGenerator.cs
+++ b/src/PatternKit.Generators/FacadeGenerator.cs
@@ -317,7 +317,7 @@ private static ImmutableArray<MethodInfo> CollectContractFirstMethods(
             : contractType.ContainingNamespace.ToDisplayString();
 
         var defaultFacadeTypeName = contractType.TypeKind == TypeKind.Interface
-            ? (contractType.Name.StartsWith("I") ? contractType.Name.Substring(1) + "Impl" : contractType.Name + "Impl")
+            ? (contractType.Name.StartsWith("I", StringComparison.Ordinal) ? contractType.Name.Substring(1) + "Impl" : contractType.Name + "Impl")
             : contractType.Name + "Impl";
 
         return new FacadeInfo(
@@ -453,15 +453,15 @@ private static bool ReturnTypesCompatible(ITypeSymbol type1, ITypeSymbol type2)
     private static bool IsAsyncMethod(IMethodSymbol method)
     {
         var returnType = method.ReturnType.ToDisplayString();
-        return returnType.StartsWith("System.Threading.Tasks.Task") ||
-               returnType.StartsWith("System.Threading.Tasks.ValueTask");
+        return returnType.StartsWith("System.Threading.Tasks.Task", StringComparison.Ordinal) ||
+               returnType.StartsWith("System.Threading.Tasks.ValueTask", StringComparison.Ordinal);
     }
 
     private static bool IsTaskLike(ITypeSymbol type)
     {
         var name = type.ToDisplayString();
-        return name.StartsWith("System.Threading.Tasks.Task") ||
-               name.StartsWith("System.Threading.Tasks.ValueTask");
+        return name.StartsWith("System.Threading.Tasks.Task", StringComparison.Ordinal) ||
+               name.StartsWith("System.Threading.Tasks.ValueTask", StringComparison.Ordinal);
     }
 
     private static ITypeSymbol UnwrapTaskType(ITypeSymbol type)
@@ -756,11 +756,11 @@ private static void GenerateContractMethod(
                 {
                     // Handle async return types
                     var returnTypeStr = methodSymbol.ReturnType.ToDisplayString();
-                    if (returnTypeStr.StartsWith("System.Threading.Tasks.ValueTask<"))
+                    if (returnTypeStr.StartsWith("System.Threading.Tasks.ValueTask<", StringComparison.Ordinal))
                     {
                         sb.AppendLine($"        return System.Threading.Tasks.ValueTask.FromResult<{GetAsyncReturnType(methodSymbol)}>(default!);");
                     }
-                    else if (returnTypeStr.StartsWith("System.Threading.Tasks.Task<"))
+                    else if (returnTypeStr.StartsWith("System.Threading.Tasks.Task<", StringComparison.Ordinal))
                     {
                         sb.AppendLine($"        return System.Threading.Tasks.Task.FromResult<{GetAsyncReturnType(methodSymbol)}>(default!);");
                     }
@@ -1013,7 +1013,7 @@ private static string GenerateAutoFacade(SourceProductionContext context, Facade
             var fieldName = g.Key;
             // Generate parameter name: if field starts with underscore, remove it; otherwise, use field name as-is
             // The parameter will be different from the field if underscore is present
-            var paramName = fieldName.StartsWith("_") ? fieldName.Substring(1) : fieldName;
+            var paramName = fieldName.StartsWith("_", StringComparison.Ordinal) ? fieldName.Substring(1) : fieldName;
             var externalType = g.First().MappingMethod!.ContainingType;
             var typeFullName = externalType.ToDisplayString(FullyQualifiedFormat);
             return $"{typeFullName} {paramName}";
@@ -1025,7 +1025,7 @@ private static string GenerateAutoFacade(SourceProductionContext context, Facade
         // Generate constructor body with null checks
         // For fields without underscore, the parameter name matches the field name, requiring `this.` qualifier for disambiguation
         foreach (var (fieldName, paramName) in groupedByField.Select(g =>
-            (g.Key, g.Key.StartsWith("_") ? g.Key.Substring(1) : g.Key)))
+            (g.Key, g.Key.StartsWith("_", StringComparison.Ordinal) ? g.Key.Substring(1) : g.Key)))
         {
             sb.AppendLine($"        this.{fieldName} = {paramName} ?? throw new System.ArgumentNullException(nameof({paramName}));");
         }
diff --git a/src/PatternKit.Generators/PrototypeGenerator.cs b/src/PatternKit.Generators/PrototypeGenerator.cs
index 819ed9bb..9827bc06 100644
--- a/src/PatternKit.Generators/PrototypeGenerator.cs
+++ b/src/PatternKit.Generators/PrototypeGenerator.cs
@@ -533,7 +533,7 @@ private bool IsImmutableReferenceType(ITypeSymbol type)
 
         // Check for known immutable collections (basic check)
         var typeName = type.ToDisplayString();
-        if (typeName.StartsWith("System.Collections.Immutable."))
+        if (typeName.StartsWith("System.Collections.Immutable.", StringComparison.Ordinal))
             return true;
 
         // Conservative: assume mutable
diff --git a/src/PatternKit.Generators/ProxyGenerator.cs b/src/PatternKit.Generators/ProxyGenerator.cs
index 04e1befa..ced5af0f 100644
--- a/src/PatternKit.Generators/ProxyGenerator.cs
+++ b/src/PatternKit.Generators/ProxyGenerator.cs
@@ -211,7 +211,7 @@ private ProxyConfig ParseProxyConfig(AttributeData attribute, INamedTypeSymbol c
 
         // Determine default proxy type name
         var baseName = contractSymbol.Name;
-        if (baseName.StartsWith("I") && baseName.Length > 1 && char.IsUpper(baseName[1]))
+        if (baseName.StartsWith("I", StringComparison.Ordinal) && baseName.Length > 1 && char.IsUpper(baseName[1]))
         {
             // Interface with I prefix: IUserService -> UserServiceProxy
             baseName = baseName.Substring(1);
@@ -592,8 +592,8 @@ private static bool IsAsyncMethod(IMethodSymbol method)
         var returnType = method.ReturnType;
         var typeName = returnType.ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat);
 
-        return typeName.StartsWith("global::System.Threading.Tasks.Task") ||
-               typeName.StartsWith("global::System.Threading.Tasks.ValueTask");
+        return typeName.StartsWith("global::System.Threading.Tasks.Task", StringComparison.Ordinal) ||
+               typeName.StartsWith("global::System.Threading.Tasks.ValueTask", StringComparison.Ordinal);
     }
 
     private static bool IsGenericAsyncReturnType(IMethodSymbol method)
@@ -615,8 +615,8 @@ private static bool IsGenericAsyncReturnType(IMethodSymbol method)
 
         return (fullName == "global::System.Threading.Tasks.Task<T>" ||
                 fullName == "global::System.Threading.Tasks.ValueTask<T>") ||
-               (namedType.Arity > 0 && (originalTypeName.StartsWith("global::System.Threading.Tasks.Task<") ||
-                originalTypeName.StartsWith("global::System.Threading.Tasks.ValueTask<")));
+               (namedType.Arity > 0 && (originalTypeName.StartsWith("global::System.Threading.Tasks.Task<", StringComparison.Ordinal) ||
+                originalTypeName.StartsWith("global::System.Threading.Tasks.ValueTask<", StringComparison.Ordinal)));
     }
 
     private static bool IsCancellationToken(ITypeSymbol type)
@@ -1490,7 +1490,7 @@ private List<string> DetermineParameterPropertyNames(List<ParameterInfo> paramet
             }
             else
             {
-                propName = char.ToUpper(param.Name[0]) + (param.Name.Length > 1 ? param.Name.Substring(1) : "");
+                propName = char.ToUpperInvariant(param.Name[0]) + (param.Name.Length > 1 ? param.Name.Substring(1) : "");
 
                 // Avoid conflicts with reserved property names
                 if (usedPropNames.Contains(propName))
diff --git a/src/PatternKit.Generators/Singleton/SingletonGenerator.cs b/src/PatternKit.Generators/Singleton/SingletonGenerator.cs
index 35a3c6f4..39bfe1d9 100644
--- a/src/PatternKit.Generators/Singleton/SingletonGenerator.cs
+++ b/src/PatternKit.Generators/Singleton/SingletonGenerator.cs
@@ -312,7 +312,7 @@ private static SingletonConfig ParseSingletonConfig(AttributeData attribute)
     private static bool HasNameConflict(INamedTypeSymbol typeSymbol, string propertyName)
     {
         // Normalize verbatim identifiers by stripping leading @
-        var normalizedName = propertyName.StartsWith("@") ? propertyName.Substring(1) : propertyName;
+        var normalizedName = propertyName.StartsWith("@", StringComparison.Ordinal) ? propertyName.Substring(1) : propertyName;
 
         // Check for existing members with the same name in declared members
         if (typeSymbol.GetMembers(normalizedName).Length > 0)
diff --git a/src/PatternKit.Generators/StateMachineGenerator.cs b/src/PatternKit.Generators/StateMachineGenerator.cs
index b048ef83..2ae785b1 100644
--- a/src/PatternKit.Generators/StateMachineGenerator.cs
+++ b/src/PatternKit.Generators/StateMachineGenerator.cs
@@ -491,7 +491,7 @@ private ImmutableArray<HookModel> CollectExitHooks(
         ulong targetValue;
         try
         {
-            targetValue = Convert.ToUInt64(constant.Value);
+            targetValue = Convert.ToUInt64(constant.Value, global::System.Globalization.CultureInfo.InvariantCulture);
         }
         catch
         {
@@ -505,7 +505,7 @@ private ImmutableArray<HookModel> CollectExitHooks(
 
             try
             {
-                var fieldValue = Convert.ToUInt64(field.ConstantValue);
+                var fieldValue = Convert.ToUInt64(field.ConstantValue, global::System.Globalization.CultureInfo.InvariantCulture);
                 if (fieldValue == targetValue)
                     return field.Name;
             }
diff --git a/src/PatternKit.Generators/VisitorGenerator.cs b/src/PatternKit.Generators/VisitorGenerator.cs
index efa21c20..e529b97b 100644
--- a/src/PatternKit.Generators/VisitorGenerator.cs
+++ b/src/PatternKit.Generators/VisitorGenerator.cs
@@ -88,7 +88,7 @@ private static string GetDefaultVisitorInterfaceName(INamedTypeSymbol baseType)
 
         // If base is an interface with I-prefix (Hungarian notation), don't add another I
         if (baseType.TypeKind == TypeKind.Interface &&
-            baseName.StartsWith("I") &&
+            baseName.StartsWith("I", StringComparison.Ordinal) &&
             baseName.Length > 1 &&
             char.IsUpper(baseName[1]))
         {
diff --git a/test/PatternKit.Generators.Tests/DecoratorGeneratorTests.cs b/test/PatternKit.Generators.Tests/DecoratorGeneratorTests.cs
index 2eb02db2..4a03e9fa 100644
--- a/test/PatternKit.Generators.Tests/DecoratorGeneratorTests.cs
+++ b/test/PatternKit.Generators.Tests/DecoratorGeneratorTests.cs
@@ -375,10 +375,10 @@ public interface IStorage
             .First(gs => gs.HintName == "TestNamespace_IStorage.Decorator.g.cs")
             .SourceText.ToString();
 
-        var appleIndex = generatedSource.IndexOf("void Apple");
-        var bananaIndex = generatedSource.IndexOf("void Banana");
-        var mangoIndex = generatedSource.IndexOf("void Mango");
-        var zebraIndex = generatedSource.IndexOf("void Zebra");
+        var appleIndex = generatedSource.IndexOf("void Apple", StringComparison.Ordinal);
+        var bananaIndex = generatedSource.IndexOf("void Banana", StringComparison.Ordinal);
+        var mangoIndex = generatedSource.IndexOf("void Mango", StringComparison.Ordinal);
+        var zebraIndex = generatedSource.IndexOf("void Zebra", StringComparison.Ordinal);
 
         ScenarioExpect.True(appleIndex < bananaIndex);
         ScenarioExpect.True(bananaIndex < mangoIndex);
diff --git a/test/PatternKit.Generators.Tests/DispatcherGeneratorTests.cs b/test/PatternKit.Generators.Tests/DispatcherGeneratorTests.cs
index 5fc0d917..d287a851 100644
--- a/test/PatternKit.Generators.Tests/DispatcherGeneratorTests.cs
+++ b/test/PatternKit.Generators.Tests/DispatcherGeneratorTests.cs
@@ -1214,7 +1214,7 @@ public static async Task<string> Run()
         var result = task.Result;
 
         // Should either be the expected result or an error message
-        if (result.StartsWith("ERROR:"))
+        if (result.StartsWith("ERROR:", StringComparison.Ordinal))
         {
             ScenarioExpect.Fail($"Test threw exception: {result}");
         }
diff --git a/test/PatternKit.Generators.Tests/FacadeGeneratorTests.cs b/test/PatternKit.Generators.Tests/FacadeGeneratorTests.cs
index 39e78442..a53d95bf 100644
--- a/test/PatternKit.Generators.Tests/FacadeGeneratorTests.cs
+++ b/test/PatternKit.Generators.Tests/FacadeGeneratorTests.cs
@@ -924,10 +924,10 @@ public static void C() { }
         var generatedSource = generatedSources.First().SourceText.ToString();
 
         // Methods should appear in alphabetical order: Alpha, Charlie, Mike, Zebra
-        var alphaIndex = generatedSource.IndexOf("void Alpha()");
-        var charlieIndex = generatedSource.IndexOf("void Charlie()");
-        var mikeIndex = generatedSource.IndexOf("void Mike()");
-        var zebraIndex = generatedSource.IndexOf("void Zebra()");
+        var alphaIndex = generatedSource.IndexOf("void Alpha()", StringComparison.Ordinal);
+        var charlieIndex = generatedSource.IndexOf("void Charlie()", StringComparison.Ordinal);
+        var mikeIndex = generatedSource.IndexOf("void Mike()", StringComparison.Ordinal);
+        var zebraIndex = generatedSource.IndexOf("void Zebra()", StringComparison.Ordinal);
 
         ScenarioExpect.True(alphaIndex < charlieIndex);
         ScenarioExpect.True(charlieIndex < mikeIndex);
diff --git a/test/PatternKit.Generators.Tests/StateMachineGeneratorTests.cs b/test/PatternKit.Generators.Tests/StateMachineGeneratorTests.cs
index 997f1290..222d9d1b 100644
--- a/test/PatternKit.Generators.Tests/StateMachineGeneratorTests.cs
+++ b/test/PatternKit.Generators.Tests/StateMachineGeneratorTests.cs
@@ -352,8 +352,8 @@ private void OnEnterPaid() { }
         ScenarioExpect.Contains("OnEnterPaid()", generatedSource);
 
         // Verify State is updated before entry hooks
-        var submitIndex = generatedSource.IndexOf("State = global::PatternKit.Examples.OrderState.Submitted");
-        var entrySubmittedIndex = generatedSource.IndexOf("OnEnterSubmitted()");
+        var submitIndex = generatedSource.IndexOf("State = global::PatternKit.Examples.OrderState.Submitted", StringComparison.Ordinal);
+        var entrySubmittedIndex = generatedSource.IndexOf("OnEnterSubmitted()", StringComparison.Ordinal);
         ScenarioExpect.True(submitIndex < entrySubmittedIndex, "State should be updated before entry hook is called");
 
         // And the updated compilation actually compiles
@@ -403,8 +403,8 @@ private void OnPay() { }
         ScenarioExpect.Contains("OnExitSubmitted()", generatedSource);
 
         // Verify exit hooks are called before transition action
-        var exitIndex = generatedSource.IndexOf("OnExitDraft()");
-        var transitionIndex = generatedSource.IndexOf("OnSubmit()");
+        var exitIndex = generatedSource.IndexOf("OnExitDraft()", StringComparison.Ordinal);
+        var transitionIndex = generatedSource.IndexOf("OnSubmit()", StringComparison.Ordinal);
         ScenarioExpect.True(exitIndex < transitionIndex, "Exit hook should be called before transition action");
 
         // And the updated compilation actually compiles
@@ -532,8 +532,8 @@ private void OnTransition() { }
 
         // Verify no exception is thrown for guard failures
         var generatedSource = result.Results[0].GeneratedSources[0].SourceText.ToString();
-        var guardFailureIndex = generatedSource.IndexOf("if (!CanTransition())");
-        var throwIndex = generatedSource.IndexOf("throw new global::System.InvalidOperationException($\"Guard failed", guardFailureIndex);
+        var guardFailureIndex = generatedSource.IndexOf("if (!CanTransition())", StringComparison.Ordinal);
+        var throwIndex = generatedSource.IndexOf("throw new global::System.InvalidOperationException($\"Guard failed", guardFailureIndex, StringComparison.Ordinal);
         ScenarioExpect.True(throwIndex == -1, "Should not throw exception on guard failure with Ignore policy");
 
         // And the updated compilation actually compiles
@@ -899,7 +899,7 @@ private async ValueTask OnTransitionAsync(CancellationToken ct)
             ScenarioExpect.True(hasGeneratedCode, "No code was generated");
 
             // Check compilation diagnostics
-            var compDiags = updated.GetDiagnostics().Where(d => d.Id.StartsWith("PKST")).ToArray();
+            var compDiags = updated.GetDiagnostics().Where(d => d.Id.StartsWith("PKST", StringComparison.Ordinal)).ToArray();
             ScenarioExpect.True(compDiags.Length > 0, $"No PKST diagnostics found. Generated code: {result.Results[0].GeneratedSources.Length} files");
         }
 
diff --git a/test/PatternKit.Generators.Tests/TemplateGeneratorTests.cs b/test/PatternKit.Generators.Tests/TemplateGeneratorTests.cs
index 4f0a9be7..ec73935c 100644
--- a/test/PatternKit.Generators.Tests/TemplateGeneratorTests.cs
+++ b/test/PatternKit.Generators.Tests/TemplateGeneratorTests.cs
@@ -182,8 +182,8 @@ private void Transform(ImportContext ctx)
             .First(gs => gs.HintName.Contains("ImportWorkflow"))
             .SourceText.ToString();
 
-        var onStartIndex = generatedSource.IndexOf("OnStart(ctx);");
-        var validateIndex = generatedSource.IndexOf("Validate(ctx);");
+        var onStartIndex = generatedSource.IndexOf("OnStart(ctx);", StringComparison.Ordinal);
+        var validateIndex = generatedSource.IndexOf("Validate(ctx);", StringComparison.Ordinal);
         ScenarioExpect.True(onStartIndex < validateIndex, "BeforeAll hook should be called before steps");
     }
 
@@ -243,8 +243,8 @@ private void OnComplete(ImportContext ctx)
             .First(gs => gs.HintName.Contains("ImportWorkflow"))
             .SourceText.ToString();
 
-        var transformIndex = generatedSource.LastIndexOf("Transform(ctx);");
-        var onCompleteIndex = generatedSource.IndexOf("OnComplete(ctx);");
+        var transformIndex = generatedSource.LastIndexOf("Transform(ctx);", StringComparison.Ordinal);
+        var onCompleteIndex = generatedSource.IndexOf("OnComplete(ctx);", StringComparison.Ordinal);
         ScenarioExpect.True(transformIndex < onCompleteIndex, "AfterAll hook should be called after steps");
     }
 
diff --git a/test/PatternKit.Generators.Tests/VisitorGeneratorTests.cs b/test/PatternKit.Generators.Tests/VisitorGeneratorTests.cs
index 931d1f56..50725335 100644
--- a/test/PatternKit.Generators.Tests/VisitorGeneratorTests.cs
+++ b/test/PatternKit.Generators.Tests/VisitorGeneratorTests.cs
@@ -849,7 +849,7 @@ public partial class ValidDerived : ValidBase { }
 
         // Should have no generator diagnostics
         var diagnostics = run.Results.SelectMany(r => r.Diagnostics)
-            .Where(d => d.Id.StartsWith("PKVIS"))
+            .Where(d => d.Id.StartsWith("PKVIS", StringComparison.Ordinal))
             .ToArray();
         ScenarioExpect.Empty(diagnostics);
     }