fix(cli): report a failed write of the MLX hostfile

The tunnel callback ignored the error of os.WriteFile and set the
hostfile variable even when the file was not written. It now logs the
error and leaves the variable alone.

Assisted-by: Claude Code:claude-sonnet-5-5 go
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

core/cli/run.go

@@ -382,7 +382,10 @@ func (r *RunCMD) Run(ctx *cliContext.Context) (result error) {
 		config.WithMLXTunnelCallback(func(tunnels []string) {
 			hostfile := filepath.Join(os.TempDir(), "localai_mlx_hostfile.json")
 			data, _ := json.Marshal(tunnels)
-			os.WriteFile(hostfile, data, 0600)
+			if err := os.WriteFile(hostfile, data, 0600); err != nil {
+				xlog.Error("failed to write MLX hostfile", "path", hostfile, "error", err)
+				return
+			}
 			os.Setenv("MLX_DISTRIBUTED_HOSTFILE", hostfile)
 			xlog.Debug("setting MLX_DISTRIBUTED_HOSTFILE", "value", hostfile, "tunnels", tunnels)
 		}),