fix: exit non-zero when use tool gets MCP-level error; replace cutString with strings.Cut

- outputToolResult() now returns an error when result.IsError is true,
  so the CLI exits 1 on MCP-level tool errors (e.g. nonexistent tool)
- Replace custom cutString() with stdlib strings.Cut (available since Go 1.18)

Agent-Logs-Url: https://github.com/advanced-security/codeql-development-mcp-server/sessions/cc25a44f-aecb-453c-be59-8064533607d3

Co-authored-by: data-douser <70299490+data-douser@users.noreply.github.com>

Author: Copilot

client/cmd/use.go

@@ -2,6 +2,7 @@ package cmd
 
 import (
 	"fmt"
+	"strings"
 
 	"github.com/spf13/cobra"
 )
@@ -21,7 +22,7 @@ Subcommands:
 func parseArgs(args []string) (map[string]string, error) {
 	result := make(map[string]string, len(args))
 	for _, a := range args {
-		key, value, found := cutString(a, "=")
+		key, value, found := strings.Cut(a, "=")
 		if !found || key == "" {
 			return nil, fmt.Errorf("invalid argument %q: expected key=value format", a)
 		}
@@ -34,7 +35,7 @@ func parseArgs(args []string) (map[string]string, error) {
 func parseArgsAny(args []string) (map[string]any, error) {
 	result := make(map[string]any, len(args))
 	for _, a := range args {
-		key, value, found := cutString(a, "=")
+		key, value, found := strings.Cut(a, "=")
 		if !found || key == "" {
 			return nil, fmt.Errorf("invalid argument %q: expected key=value format", a)
 		}
@@ -43,16 +44,6 @@ func parseArgsAny(args []string) (map[string]any, error) {
 	return result, nil
 }
 
-// cutString splits s around the first instance of sep.
-func cutString(s, sep string) (before, after string, found bool) {
-	for i := 0; i+len(sep) <= len(s); i++ {
-		if s[i:i+len(sep)] == sep {
-			return s[:i], s[i+len(sep):], true
-		}
-	}
-	return s, "", false
-}
-
 func init() {
 	rootCmd.AddCommand(useCmd)
 }

client/cmd/use_tool.go

@@ -65,5 +65,8 @@ func outputToolResult(result *mcpclient.ToolResult) error {
 	default:
 		fmt.Fprint(os.Stdout, mcpclient.FormatToolResultText(result))
 	}
+	if result.IsError {
+		return fmt.Errorf("tool returned error")
+	}
 	return nil
 }