Add ModelContextProtocol.Core package (#428)

src/ModelContextProtocol.Core/McpErrorCode.cs

@@ -0,0 +1,49 @@
+namespace ModelContextProtocol;
+
+/// <summary>
+/// Represents standard JSON-RPC error codes as defined in the MCP specification.
+/// </summary>
+public enum McpErrorCode
+{
+    /// <summary>
+    /// Indicates that the JSON received could not be parsed.
+    /// </summary>
+    /// <remarks>
+    /// This error occurs when the input contains malformed JSON or incorrect syntax.
+    /// </remarks>
+    ParseError = -32700,
+
+    /// <summary>
+    /// Indicates that the JSON payload does not conform to the expected Request object structure.
+    /// </summary>
+    /// <remarks>
+    /// The request is considered invalid if it lacks required fields or fails to follow the JSON-RPC protocol.
+    /// </remarks>
+    InvalidRequest = -32600,
+
+    /// <summary>
+    /// Indicates that the requested method does not exist or is not available on the server.
+    /// </summary>
+    /// <remarks>
+    /// This error is returned when the method name specified in the request cannot be found.
+    /// </remarks>
+    MethodNotFound = -32601,
+
+    /// <summary>
+    /// Indicates that one or more parameters provided in the request are invalid.
+    /// </summary>
+    /// <remarks>
+    /// This error is returned when the parameters do not match the expected method signature or constraints.
+    /// This includes cases where required parameters are missing or not understood, such as when a name for
+    /// a tool or prompt is not recognized.
+    /// </remarks>
+    InvalidParams = -32602,
+
+    /// <summary>
+    /// Indicates that an internal error occurred while processing the request.
+    /// </summary>
+    /// <remarks>
+    /// This error is used when the endpoint encounters an unexpected condition that prevents it from fulfilling the request.
+    /// </remarks>
+    InternalError = -32603,
+}