Strengthen Assert.NotNull(deserialized.Meta) to validate actual content

Replace weak Assert.NotNull(deserialized.Meta) assertions with proper
content validation in all 40 Protocol test files. Each assertion now
verifies the actual key-value pair set in the test's Meta property.

Co-authored-by: Copilot <[email protected]>

Author: Copilot

tests/ModelContextProtocol.Tests/Protocol/CallToolRequestParamsTests.cs

@@ -33,6 +33,7 @@ public static void CallToolRequestParams_SerializationRoundTrip_PreservesAllProp
         Assert.NotNull(deserialized.Task);
         Assert.Equal(original.Task.TimeToLive, deserialized.Task.TimeToLive);
         Assert.NotNull(deserialized.Meta);
+        Assert.Equal("token-123", (string)deserialized.Meta["progressToken"]!);
     }
 
     [Fact]

tests/ModelContextProtocol.Tests/Protocol/CallToolResultTests.cs

@@ -37,6 +37,7 @@ public static void CallToolResult_SerializationRoundTrip_PreservesAllProperties(
         Assert.NotNull(deserialized.Task);
         Assert.Equal("task-1", deserialized.Task.TaskId);
         Assert.NotNull(deserialized.Meta);
+        Assert.Equal("value", (string)deserialized.Meta["key"]!);
     }
 
     [Fact]

tests/ModelContextProtocol.Tests/Protocol/CancelledNotificationParamsTests.cs

@@ -23,6 +23,7 @@ public static void CancelledNotificationParams_SerializationRoundTrip_PreservesA
         Assert.Equal(original.RequestId, deserialized.RequestId);
         Assert.Equal(original.Reason, deserialized.Reason);
         Assert.NotNull(deserialized.Meta);
+        Assert.Equal("value", (string)deserialized.Meta["key"]!);
     }
 
     [Fact]

tests/ModelContextProtocol.Tests/Protocol/CompleteRequestParamsTests.cs

@@ -32,6 +32,7 @@ public static void CompleteRequestParams_SerializationRoundTrip_PreservesAllProp
         Assert.NotNull(deserialized.Context.Arguments);
         Assert.Equal("en", deserialized.Context.Arguments["language"]);
         Assert.NotNull(deserialized.Meta);
+        Assert.Equal("tok-1", (string)deserialized.Meta["progressToken"]!);
     }
 
     [Fact]

tests/ModelContextProtocol.Tests/Protocol/CompleteResultTests.cs

@@ -32,6 +32,7 @@ public static void CompleteResult_SerializationRoundTrip_PreservesAllProperties(
         Assert.Equal(10, deserialized.Completion.Total);
         Assert.True(deserialized.Completion.HasMore);
         Assert.NotNull(deserialized.Meta);
+        Assert.Equal("value", (string)deserialized.Meta["key"]!);
     }
 
     [Fact]

tests/ModelContextProtocol.Tests/Protocol/CreateMessageResultTests.cs

@@ -164,6 +164,7 @@ public void CreateMessageResult_RoundTripWithAllFields()
         Assert.Equal(2, deserialized.Content.Count);
         Assert.Equal("toolUse", deserialized.StopReason);
         Assert.NotNull(deserialized.Meta);
+        Assert.Equal("metadata", (string)deserialized.Meta["custom"]!);
     }
 
     [Fact]

tests/ModelContextProtocol.Tests/Protocol/CreateTaskResultTests.cs

@@ -36,5 +36,6 @@ public static void CreateTaskResult_SerializationRoundTrip_PreservesAllPropertie
         Assert.Equal(original.Task.TimeToLive, deserialized.Task.TimeToLive);
         Assert.Equal(original.Task.PollInterval, deserialized.Task.PollInterval);
         Assert.NotNull(deserialized.Meta);
+        Assert.Equal("value", (string)deserialized.Meta["key"]!);
     }
 }

tests/ModelContextProtocol.Tests/Protocol/ElicitRequestParamsTests.cs

@@ -40,6 +40,7 @@ public static void ElicitRequestParams_SerializationRoundTrip_PreservesAllProper
         Assert.NotNull(deserialized.Task);
         Assert.Equal(TimeSpan.FromMinutes(10), deserialized.Task.TimeToLive);
         Assert.NotNull(deserialized.Meta);
+        Assert.Equal("tok-1", (string)deserialized.Meta["progressToken"]!);
     }
 
     [Fact]

tests/ModelContextProtocol.Tests/Protocol/ElicitResultTests.cs

@@ -31,6 +31,7 @@ public static void ElicitResult_SerializationRoundTrip_PreservesAllProperties()
         Assert.Equal("John", deserialized.Content["name"].GetString());
         Assert.Equal(30, deserialized.Content["age"].GetInt32());
         Assert.NotNull(deserialized.Meta);
+        Assert.Equal("value", (string)deserialized.Meta["key"]!);
     }
 
     [Fact]

tests/ModelContextProtocol.Tests/Protocol/ElicitationCompleteNotificationParamsTests.cs

@@ -21,6 +21,7 @@ public static void ElicitationCompleteNotificationParams_SerializationRoundTrip_
         Assert.NotNull(deserialized);
         Assert.Equal("elicit-abc-123", deserialized.ElicitationId);
         Assert.NotNull(deserialized.Meta);
+        Assert.Equal("value", (string)deserialized.Meta["key"]!);
     }
 
     [Fact]