Remove FMED006 as we can't know if a handler exists in another project

Author: ejsmith

src/Foundatio.Mediator/HandlerGenerator.cs

@@ -660,25 +660,10 @@ private static void ValidateCallSite(SourceProductionContext context, CallSiteIn
             return; // Only validate Invoke calls, not Publish
 
         // If the message is a generic type parameter (e.g., T), we cannot know the handler at compile time,
-        // so do not emit FMED006/FMDE007 for missing/multiple handlers.
+        // so do not emit FMDE007 for missing/multiple handlers.
         if (callSite.MessageType.IsTypeParameter)
             return;
 
-        // FMED006: No handler found for invoke call
-        if (handlersForMessage.Count == 0)
-        {
-            var diagnostic = new DiagnosticInfo
-            {
-                Identifier = "FMED006",
-                Title = "No handler found for message",
-                Message = $"No handler found for message type '{callSite.MessageType.FullName}'. Invoke calls require exactly one handler.",
-                Severity = DiagnosticSeverity.Error,
-                Location = callSite.Location
-            };
-            context.ReportDiagnostic(diagnostic.ToDiagnostic());
-            return;
-        }
-
         // FMED007: Multiple handlers found for invoke call
         if (handlersForMessage.Count > 1)
         {

tests/Foundatio.Mediator.Tests/DiagnosticValidationTests.cs

@@ -4,29 +4,6 @@ public class DiagnosticValidationTests : GeneratorTestBase
 {
 	private static readonly MediatorGenerator Gen = new();
 
-	[Fact]
-    public void FMED006_NoHandlerForInvoke()
-	{
-		var src = """
-			using System.Threading;
-			using System.Threading.Tasks;
-			using Foundatio.Mediator;
-
-			public record Msg;
-			public record Other;
-			public class OtherHandler { public Task HandleAsync(Other m, CancellationToken ct) => Task.CompletedTask; }
-
-			public static class Calls {
-				public static async Task Call(IMediator m) {
-					await m.InvokeAsync(new Msg());
-				}
-			}
-			""";
-
-		var (_, genDiags, _) = RunGenerator(src, [ Gen ]);
-		Assert.Contains(genDiags, d => d.Id == "FMED006");
-	}
-
 	[Fact]
 	public void FMED007_MultipleHandlersForInvoke()
 	{
@@ -126,7 +103,6 @@ public static async Task Call<T>(IMediator m, T msg) {
 			""";
 
 		var (_, genDiags, _) = RunGenerator(src, [ Gen ]);
-		Assert.DoesNotContain(genDiags, d => d.Id == "FMED006");
+		Assert.DoesNotContain(genDiags, d => d.Id == "FMED007");
 	}
 }
-