Add validation to UseDisabledWhen() for correct call ordering

Directory.Build.props

@@ -21,7 +21,7 @@
 
   <!-- Centralized versioning -->
   <PropertyGroup>
-    <VersionPrefix>1.0.0</VersionPrefix>
+    <VersionPrefix>1.0.1</VersionPrefix>
     <VersionSuffix>prerelease</VersionSuffix>
   </PropertyGroup>
 

src/AzureFunctions.DisabledWhen/IFunctionsWorkerApplicationBuilderExtensions.cs

@@ -9,6 +9,18 @@ public static class IFunctionsWorkerApplicationBuilderExtensions
 {
     public static void UseDisabledWhen(this IFunctionsWorkerApplicationBuilder builder)
     {
+        // Validate that an underlying IFunctionMetadataProvider is already registered
+        // This is typically done by ConfigureFunctionsWebApplication() or ConfigureFunctionsWorkerDefaults()
+        var hasUnderlyingProvider = builder.Services.Any(descriptor => 
+            descriptor.ServiceType == typeof(IFunctionMetadataProvider));
+
+        if (!hasUnderlyingProvider)
+        {
+            throw new InvalidOperationException(
+                "UseDisabledWhen() must be called after ConfigureFunctionsWebApplication() or ConfigureFunctionsWorkerDefaults(). " +
+                "No underlying IFunctionMetadataProvider was found in the service collection.");
+        }
+
         builder.Services.AddSingleton<IFunctionMetadataProvider, DisabledWhenMetadataProvider>();
     }
 }

tests/AzureFunctions.DisabledWhen.Tests/AppBuilderStartupTests.cs

@@ -89,4 +89,5 @@ await testHost.StartAsync(new Dictionary<string, string?>
         await Assert.That(functionNames).Contains("AlwaysEnabled");
         await Assert.That(functionNames).DoesNotContain("RequiresApiKey");
     }
+
 }