Move McpHeaderEncoder from Client to Protocol namespace

McpHeaderEncoder is a shared utility used by both client-side (McpHeaderExtractor)
and server-side (StreamableHttpHandler) code. Placing it in the Client namespace
forced server code to reference ModelContextProtocol.Client, creating a misleading
dependency. Move it to ModelContextProtocol.Protocol alongside McpHttpHeaders where
it logically belongs as a transport-level concern.

Author: Tarek Mahmoud Sayed

src/ModelContextProtocol.AspNetCore/StreamableHttpHandler.cs

@@ -732,7 +732,7 @@ argForMissing is not null &&
                 return false;
             }
 
-            var decodedActual = Client.McpHeaderEncoder.DecodeValue(actualHeaderValue);
+            var decodedActual = McpHeaderEncoder.DecodeValue(actualHeaderValue);
             if (decodedActual is null)
             {
                 errorMessage = $"Header mismatch: {fullHeaderName} header contains invalid Base64 encoding.";
@@ -747,7 +747,7 @@ argForMissing is not null &&
                 var expectedHeaderValue = ConvertJsonNodeToHeaderValue(argNode);
                 if (expectedHeaderValue is not null)
                 {
-                    var decodedExpected = Client.McpHeaderEncoder.DecodeValue(expectedHeaderValue);
+                    var decodedExpected = McpHeaderEncoder.DecodeValue(expectedHeaderValue);
                     if (!string.Equals(decodedActual, decodedExpected, StringComparison.Ordinal))
                     {
                         errorMessage = $"Header mismatch: {fullHeaderName} header value does not match body argument '{property.Name}'.";
@@ -807,7 +807,7 @@ private static bool IsValidHeaderValue(string value)
             _ => null
         };
 
-        return Client.McpHeaderEncoder.EncodeValue(value);
+        return McpHeaderEncoder.EncodeValue(value);
     }
 
     private static bool MatchesApplicationJsonMediaType(MediaTypeHeaderValue acceptHeaderValue)

…Protocol.Core/Client/McpHeaderEncoder.cs …otocol.Core/Protocol/McpHeaderEncoder.cssrc/ModelContextProtocol.Core/Client/McpHeaderEncoder.cs renamed to src/ModelContextProtocol.Core/Protocol/McpHeaderEncoder.cs src/ModelContextProtocol.Core/Client/McpHeaderEncoder.cs renamed to src/ModelContextProtocol.Core/Protocol/McpHeaderEncoder.cs

@@ -1,7 +1,6 @@
 using System.Text;
-using ModelContextProtocol.Protocol;
 
-namespace ModelContextProtocol.Client;
+namespace ModelContextProtocol.Protocol;
 
 /// <summary>
 /// Encodes and decodes parameter values for use in MCP HTTP headers according to the

tests/ModelContextProtocol.AspNetCore.Tests/Sep2243HeaderTests.cs

@@ -1,7 +1,6 @@
 using Microsoft.AspNetCore.Builder;
 using Microsoft.Extensions.DependencyInjection;
 using ModelContextProtocol.AspNetCore.Tests.Utils;
-using ModelContextProtocol.Client;
 using ModelContextProtocol.Protocol;
 using ModelContextProtocol.Server;
 using ModelContextProtocol.Tests.Utils;

tests/ModelContextProtocol.Tests/Client/McpHeaderEncoderTests.cs

@@ -1,4 +1,4 @@
-using ModelContextProtocol.Client;
+using ModelContextProtocol.Protocol;
 
 namespace ModelContextProtocol.Tests.Client;