Deprecate McpErrorCode.ResourceNotFound (-32002) and use McpErrorCode.InvalidParams (-32602) per SEP-2164 (#1558)

tests/ModelContextProtocol.Tests/Configuration/McpServerBuilderExtensionsResourcesTests.cs

@@ -109,7 +109,7 @@ public partial class McpServerBuilderExtensionsResourcesTests : ClientServerTest
                     };
             }
 
-            throw new McpProtocolException($"Resource not found: {request.Params.Uri}", McpErrorCode.ResourceNotFound);
+            throw new McpProtocolException($"Resource not found: {request.Params.Uri}", McpErrorCode.InvalidParams);
         })
         .WithResources<SimpleResources>();
     }
@@ -317,7 +317,7 @@ public partial class McpServerBuilderExtensionsResourcesTests : ClientServerTest
             cancellationToken: TestContext.Current.CancellationToken));
 
         Assert.Contains("Resource not found", e.Message);
-        Assert.Equal(McpErrorCode.ResourceNotFound, e.ErrorCode);
+        Assert.Equal(McpErrorCode.InvalidParams, e.ErrorCode);
     }
 
     [Fact]

tests/ModelContextProtocol.Tests/Configuration/McpServerResourceRoutingTests.cs

@@ -1,4 +1,5 @@
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Options;
 using ModelContextProtocol.Client;
 using ModelContextProtocol.Protocol;
 using ModelContextProtocol.Server;
@@ -22,6 +23,23 @@ public sealed class McpServerResourceRoutingTests(ITestOutputHelper testOutputHe
         return await CreateMcpClientForServer();
     }
 
+    /// <summary>
+    /// Starts the server with the specified resources, pins both the server's and the
+    /// client's protocol version to <paramref name="protocolVersion"/>, and returns a
+    /// connected client. Both ends must be pinned because <see cref="McpClient"/> strictly
+    /// compares the server's negotiated version against the client's requested version and
+    /// refuses to connect on mismatch.
+    /// </summary>
+    private async Task<McpClient> CreateClientWithResourcesAndServerVersionAsync(
+        string protocolVersion,
+        params McpServerResource[] resources)
+    {
+        McpServerBuilder.WithResources(resources);
+        McpServerBuilder.Services.Configure<McpServerOptions>(o => o.ProtocolVersion = protocolVersion);
+        StartServer();
+        return await CreateMcpClientForServer(new McpClientOptions { ProtocolVersion = protocolVersion });
+    }
+
     /// <summary>
     /// Asserts that the given URI matches the template and produces the expected text result.
     /// </summary>
@@ -56,6 +74,26 @@ public sealed class McpServerResourceRoutingTests(ITestOutputHelper testOutputHe
         Assert.Equal(McpErrorCode.ResourceNotFound, ex.ErrorCode);
     }
 
+    // Unknown-resource-URI responses are version-gated: older clients keep the legacy
+    // -32002 (McpErrorCode.ResourceNotFound), and clients on the draft protocol version that
+    // moves to the standard JSON-RPC code see -32602 (McpErrorCode.InvalidParams).
+    [Theory]
+    [InlineData("2025-11-25", McpErrorCode.ResourceNotFound)]
+    [InlineData("DRAFT-2026-v1", McpErrorCode.InvalidParams)]
+    public async Task ResourceNotFound_ErrorCode_IsVersionGated(string serverProtocolVersion, McpErrorCode expectedCode)
+    {
+        var resource = McpServerResource.Create(
+            options: new() { UriTemplate = "test://known/{id}" },
+            method: (string id) => $"ok: {id}");
+
+        var client = await CreateClientWithResourcesAndServerVersionAsync(serverProtocolVersion, resource);
+
+        var ex = await Assert.ThrowsAsync<McpProtocolException>(async () =>
+            await client.ReadResourceAsync("test://unknown", null, TestContext.Current.CancellationToken));
+
+        Assert.Equal(expectedCode, ex.ErrorCode);
+    }
+
     /// <summary>
     /// Verify that when multiple templated resources exist, the correct one is matched based on the URI pattern.
     /// Regression test for https://github.com/modelcontextprotocol/csharp-sdk/issues/821.

tests/ModelContextProtocol.Tests/McpProtocolExceptionDataTests.cs

@@ -33,7 +33,7 @@ public class McpProtocolExceptionDataTests : ClientServerTestBase
             switch (toolName)
             {
                 case "throw_with_serializable_data":
-                    throw new McpProtocolException("Resource not found", McpErrorCode.ResourceNotFound)
+                    throw new McpProtocolException("Resource not found", McpErrorCode.InvalidParams)
                     {
                         Data =
                         {
@@ -43,7 +43,7 @@ public class McpProtocolExceptionDataTests : ClientServerTestBase
                     };
 
                 case "throw_with_nonserializable_data":
-                    throw new McpProtocolException("Resource not found", McpErrorCode.ResourceNotFound)
+                    throw new McpProtocolException("Resource not found", McpErrorCode.InvalidParams)
                     {
                         Data =
                         {
@@ -55,7 +55,7 @@ public class McpProtocolExceptionDataTests : ClientServerTestBase
                     };
 
                 case "throw_with_only_nonserializable_data":
-                    throw new McpProtocolException("Resource not found", McpErrorCode.ResourceNotFound)
+                    throw new McpProtocolException("Resource not found", McpErrorCode.InvalidParams)
                     {
                         Data =
                         {
@@ -79,7 +79,7 @@ public class McpProtocolExceptionDataTests : ClientServerTestBase
             await client.CallToolAsync("throw_with_serializable_data", cancellationToken: TestContext.Current.CancellationToken));
 
         Assert.Equal("Request failed (remote): Resource not found", exception.Message);
-        Assert.Equal(McpErrorCode.ResourceNotFound, exception.ErrorCode);
+        Assert.Equal(McpErrorCode.InvalidParams, exception.ErrorCode);
 
         // Verify the data was propagated to the exception
         // The Data collection should contain the expected keys
@@ -113,7 +113,7 @@ public class McpProtocolExceptionDataTests : ClientServerTestBase
             await client.CallToolAsync("throw_with_nonserializable_data", cancellationToken: TestContext.Current.CancellationToken));
 
         Assert.Equal("Request failed (remote): Resource not found", exception.Message);
-        Assert.Equal(McpErrorCode.ResourceNotFound, exception.ErrorCode);
+        Assert.Equal(McpErrorCode.InvalidParams, exception.ErrorCode);
 
         // Verify that only the serializable data was propagated (non-serializable was filtered out)
         var hasUri = false;
@@ -142,7 +142,7 @@ public class McpProtocolExceptionDataTests : ClientServerTestBase
             await client.CallToolAsync("throw_with_only_nonserializable_data", cancellationToken: TestContext.Current.CancellationToken));
 
         Assert.Equal("Request failed (remote): Resource not found", exception.Message);
-        Assert.Equal(McpErrorCode.ResourceNotFound, exception.ErrorCode);
+        Assert.Equal(McpErrorCode.InvalidParams, exception.ErrorCode);
         
         // When all data is non-serializable, the Data collection should be empty
         // (the server's ConvertExceptionData returns null when no serializable data exists)

tests/ModelContextProtocol.Tests/Server/McpServerTests.cs

@@ -1033,7 +1033,7 @@ public class McpServerTests : LoggedTest
     public async Task Can_Handle_Call_Tool_Requests_With_McpProtocolException_And_Data()
     {
         const string ErrorMessage = "Resource not found";
-        const McpErrorCode ErrorCode = McpErrorCode.ResourceNotFound;
+        const McpErrorCode ErrorCode = McpErrorCode.InvalidParams;
         const string ResourceUri = "file:///path/to/resource";
 
         await using var transport = new TestServerTransport();