test: Add mcp_runtime_variables-t to verify runtime_global_variables

New TAP test that verifies MCP variables are correctly populated into
runtime_global_variables after LOAD MCP VARIABLES TO RUNTIME:

1. Verifies runtime_global_variables contains at least 10 MCP variables
2. Changes multiple variables (timeout_ms, queries_max, processlist_max)
3. Verifies changed values are reflected in runtime_global_variables
4. Verifies runtime values match global_variables

test/tap/groups/groups.json

@@ -280,6 +280,7 @@
   "mcp_mysql_concurrency_stress-t": [ "ai-g1" ],
   "mcp_pgsql_concurrency_stress-t": [ "ai-g1" ],
   "mcp_query_run_sql_readonly-t": [ "ai-g1" ],
+  "mcp_runtime_variables-t": [ "ai-g1" ],
   "mcp_show_connections_commands_inmemory-t": [ "ai-g1" ],
   "mcp_show_queries_topk-t": [ "ai-g1" ],
   "mcp_stats_refresh-t": [ "ai-g1" ],

test/tap/tests/mcp_runtime_variables-t.cpp

@@ -0,0 +1,166 @@
+/**
+ * @file mcp_runtime_variables-t.cpp
+ * @brief TAP test for MCP runtime_global_variables table population.
+ *
+ * This test verifies that MCP variables are correctly populated into
+ * runtime_global_variables after LOAD MCP VARIABLES TO RUNTIME.
+ *
+ * Test cases:
+ * 1. Verify runtime_global_variables contains MCP variables after LOAD
+ * 2. Verify changed variables are reflected in runtime_global_variables after LOAD
+ * 3. Verify runtime values match the values set in memory
+ */
+
+#include <string>
+#include <cstring>
+#include <cstdio>
+
+#include "mysql.h"
+#include "mysqld_error.h"
+
+#include "tap.h"
+#include "command_line.h"
+#include "utils.h"
+
+using std::string;
+
+/**
+ * @brief Get the value of a variable from runtime_global_variables
+ *
+ * @param admin MySQL connection to admin interface
+ * @param var_name Variable name (with mcp- prefix)
+ * @return std::string The variable value, or empty string if not found
+ */
+string get_runtime_variable(MYSQL* admin, const string& var_name) {
+	string query = "SELECT variable_value FROM runtime_global_variables WHERE variable_name='" + var_name + "'";
+	if (mysql_query(admin, query.c_str()) != 0) {
+		return "";
+	}
+
+	MYSQL_RES* res = mysql_store_result(admin);
+	if (!res) {
+		return "";
+	}
+
+	MYSQL_ROW row = mysql_fetch_row(res);
+	string value = row && row[0] ? row[0] : "";
+
+	mysql_free_result(res);
+	return value;
+}
+
+/**
+ * @brief Count MCP variables in runtime_global_variables
+ *
+ * @param admin MySQL connection to admin interface
+ * @return int Number of mcp-* variables in runtime_global_variables
+ */
+int count_mcp_runtime_variables(MYSQL* admin) {
+	if (mysql_query(admin, "SELECT COUNT(*) FROM runtime_global_variables WHERE variable_name LIKE 'mcp-%'") != 0) {
+		return -1;
+	}
+
+	MYSQL_RES* res = mysql_store_result(admin);
+	if (!res) {
+		return -1;
+	}
+
+	MYSQL_ROW row = mysql_fetch_row(res);
+	int count = row && row[0] ? atoi(row[0]) : 0;
+
+	mysql_free_result(res);
+	return count;
+}
+
+int main(int argc, char** argv) {
+	(void)argc;
+	(void)argv;
+
+	CommandLine cl;
+	if (cl.getEnv()) {
+		diag("Failed to read TAP environment");
+		return exit_status();
+	}
+
+	plan(8);
+
+	MYSQL* admin = init_mysql_conn(cl.admin_host, cl.admin_port, cl.admin_username, cl.admin_password);
+	if (!admin) {
+		skip(8, "Cannot connect to admin");
+		return exit_status();
+	}
+	ok(admin != nullptr, "Admin connection established");
+
+	// Test 1: Verify runtime_global_variables has at least 10 MCP variables after LOAD
+	diag("Test 1: Verifying runtime_global_variables is populated with MCP variables");
+
+	// First, ensure we have a clean state and load to runtime
+	run_q(admin, "SET mcp-enabled=false");
+	run_q(admin, "LOAD MCP VARIABLES TO RUNTIME");
+
+	int count = count_mcp_runtime_variables(admin);
+	ok(count >= 10, "runtime_global_variables contains at least 10 MCP variables (got %d)", count);
+
+	// Test 2: Change several variables and verify they update in runtime_global_variables
+	diag("Test 2: Changing variables and verifying runtime_global_variables updates");
+
+	// Record original values
+	string orig_timeout = get_runtime_variable(admin, "mcp-timeout_ms");
+	string orig_queries_max = get_runtime_variable(admin, "mcp-stats_show_queries_max_rows");
+	string orig_processlist_max = get_runtime_variable(admin, "mcp-stats_show_processlist_max_rows");
+
+	diag("Original values: timeout_ms=%s, queries_max=%s, processlist_max=%s",
+		orig_timeout.c_str(), orig_queries_max.c_str(), orig_processlist_max.c_str());
+
+	// Change the variables
+	run_q(admin, "SET mcp-timeout_ms=45000");
+	run_q(admin, "SET mcp-stats_show_queries_max_rows=500");
+	run_q(admin, "SET mcp-stats_show_processlist_max_rows=300");
+
+	// Load to runtime
+	run_q(admin, "LOAD MCP VARIABLES TO RUNTIME");
+
+	// Verify the values changed in runtime_global_variables
+	string new_timeout = get_runtime_variable(admin, "mcp-timeout_ms");
+	string new_queries_max = get_runtime_variable(admin, "mcp-stats_show_queries_max_rows");
+	string new_processlist_max = get_runtime_variable(admin, "mcp-stats_show_processlist_max_rows");
+
+	diag("New values: timeout_ms=%s, queries_max=%s, processlist_max=%s",
+		new_timeout.c_str(), new_queries_max.c_str(), new_processlist_max.c_str());
+
+	ok(new_timeout == "45000", "mcp-timeout_ms updated to 45000 in runtime_global_variables (got '%s')", new_timeout.c_str());
+	ok(new_queries_max == "500", "mcp-stats_show_queries_max_rows updated to 500 in runtime_global_variables (got '%s')", new_queries_max.c_str());
+	ok(new_processlist_max == "300", "mcp-stats_show_processlist_max_rows updated to 300 in runtime_global_variables (got '%s')", new_processlist_max.c_str());
+
+	// Test 3: Verify runtime values match global_variables
+	diag("Test 3: Verifying runtime_global_variables matches global_variables");
+
+	// Get values from global_variables
+	string global_timeout = get_mcp_variable(admin, "timeout_ms");
+	string global_queries = get_mcp_variable(admin, "stats_show_queries_max_rows");
+	string global_processlist = get_mcp_variable(admin, "stats_show_processlist_max_rows");
+
+	ok(new_timeout == global_timeout, "runtime timeout_ms (%s) matches global_variables (%s)",
+		new_timeout.c_str(), global_timeout.c_str());
+	ok(new_queries_max == global_queries, "runtime queries_max (%s) matches global_variables (%s)",
+		new_queries_max.c_str(), global_queries.c_str());
+	ok(new_processlist_max == global_processlist, "runtime processlist_max (%s) matches global_variables (%s)",
+		new_processlist_max.c_str(), global_processlist.c_str());
+
+	// Cleanup: restore original values
+	diag("Cleanup: Restoring original values");
+	if (!orig_timeout.empty()) {
+		run_q(admin, ("SET mcp-timeout_ms=" + orig_timeout).c_str());
+	}
+	if (!orig_queries_max.empty()) {
+		run_q(admin, ("SET mcp-stats_show_queries_max_rows=" + orig_queries_max).c_str());
+	}
+	if (!orig_processlist_max.empty()) {
+		run_q(admin, ("SET mcp-stats_show_processlist_max_rows=" + orig_processlist_max).c_str());
+	}
+	run_q(admin, "LOAD MCP VARIABLES TO RUNTIME");
+
+	mysql_close(admin);
+
+	return exit_status();
+}