feat: Improve MCP error logging with request payloads

Exception handlers now log the full request payload that caused the error,
making debugging much easier.

Changes:
- Move req_body/req_path declarations outside try block so catch handlers can access them
- Log request payload in all exception handlers (parse errors, std::exception, and catch-all)
- Log tool arguments when tool execution fails

Previously, exceptions would only log the error message without context,
making it impossible to reproduce the issue. Now the full payload is logged.

lib/MCP_Endpoint.cpp

@@ -127,6 +127,10 @@ std::string MCP_JSONRPC_Resource::create_jsonrpc_error(
 std::shared_ptr<http_response> MCP_JSONRPC_Resource::handle_jsonrpc_request(
 	const httpserver::http_request& req
 ) {
+	// Declare these outside the try block so they're available in catch handlers
+	std::string req_body;
+	std::string req_path;
+
 	// Wrap entire request handling in try-catch to catch any unexpected exceptions
 	try {
 		// Update statistics
@@ -134,9 +138,9 @@ std::shared_ptr<http_response> MCP_JSONRPC_Resource::handle_jsonrpc_request(
 			handler->status_variables.total_requests++;
 		}
 
-		// Get request body
-		std::string req_body = req.get_content();
-		std::string req_path = req.get_path();
+		// Get request body and path
+		req_body = req.get_content();
+		req_path = req.get_path();
 
 		proxy_debug(PROXY_DEBUG_GENERIC, 2, "MCP request on %s: %s\n", req_path.c_str(), req_body.c_str());
 
@@ -146,6 +150,7 @@ std::shared_ptr<http_response> MCP_JSONRPC_Resource::handle_jsonrpc_request(
 			req_json = json::parse(req_body);
 		} catch (json::parse_error& e) {
 		proxy_error("MCP request on %s: Invalid JSON - %s\n", req_path.c_str(), e.what());
+		proxy_error("MCP request payload that failed to parse: %s\n", req_body.c_str());
 		if (handler) {
 			handler->status_variables.failed_requests++;
 		}
@@ -256,8 +261,8 @@ std::shared_ptr<http_response> MCP_JSONRPC_Resource::handle_jsonrpc_request(
 
 	} catch (const std::exception& e) {
 		// Catch any unexpected exceptions and return a proper error response
-		std::string req_path = req.get_path();
 		proxy_error("MCP request on %s: Unexpected exception - %s\n", req_path.c_str(), e.what());
+		proxy_error("MCP request payload that caused exception: %s\n", req_body.c_str());
 		if (handler) {
 			handler->status_variables.failed_requests++;
 		}
@@ -269,8 +274,8 @@ std::shared_ptr<http_response> MCP_JSONRPC_Resource::handle_jsonrpc_request(
 		return response;
 	} catch (...) {
 		// Catch any other exceptions
-		std::string req_path = req.get_path();
 		proxy_error("MCP request on %s: Unknown exception\n", req_path.c_str());
+		proxy_error("MCP request payload that caused exception: %s\n", req_body.c_str());
 		if (handler) {
 			handler->status_variables.failed_requests++;
 		}
@@ -379,10 +384,12 @@ json MCP_JSONRPC_Resource::handle_tools_call(const json& req_json) {
 	if (response.is_object() && response.contains("success") && response.contains("result")) {
 		bool success = response["success"].get<bool>();
 		if (!success) {
-			// Tool execution failed - log the error and return in MCP format
+			// Tool execution failed - log the error with full context and return in MCP format
 			std::string error_msg = response.contains("error") ? response["error"].get<std::string>() : "Tool execution failed";
+			std::string args_str = arguments.dump();
 			proxy_error("MCP TOOL CALL FAILED: endpoint='%s' tool='%s' error='%s'\n",
 				endpoint_name.c_str(), tool_name.c_str(), error_msg.c_str());
+			proxy_error("MCP TOOL CALL FAILED: arguments='%s'\n", args_str.c_str());
 			json mcp_result;
 			mcp_result["content"] = json::array();
 			json error_content;