Add cmux CLI relay and tests

- Introduce CLI client (cmux) to relay v1 text and v2 JSON-RPC commands over Unix/TCP sockets
- Implement command specs, flag parsing, v1/v2 round-trips, TCP retry with address refresh
- Add browser subcommand mapping and rpc passthrough support
- Support busybox-style invocation when argv[0]=="cmux" and add 'cli' subcommand
- Add comprehensive unit tests for socket dialing, CLI commands, flag-to-param mapping, and env defaults
- Add socket_addr file fallback reader and random request id generation

daemon/remote/cmd/cmuxd-remote/main.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"path/filepath"
 )
 
 var version = "dev"
@@ -30,6 +31,11 @@ type rpcResponse struct {
 }
 
 func main() {
+	// Busybox-style: if invoked as "cmux" (via symlink), act as CLI relay.
+	base := filepath.Base(os.Args[0])
+	if base == "cmux" {
+		os.Exit(runCLI(os.Args[1:]))
+	}
 	os.Exit(run(os.Args[1:], os.Stdin, os.Stdout, os.Stderr))
 }
 
@@ -59,6 +65,8 @@ func run(args []string, stdin io.Reader, stdout, stderr io.Writer) int {
 			return 1
 		}
 		return 0
+	case "cli":
+		return runCLI(args[1:])
 	default:
 		usage(stderr)
 		return 2
@@ -69,6 +77,7 @@ func usage(w io.Writer) {
 	_, _ = fmt.Fprintln(w, "Usage:")
 	_, _ = fmt.Fprintln(w, "  cmuxd-remote version")
 	_, _ = fmt.Fprintln(w, "  cmuxd-remote serve --stdio")
+	_, _ = fmt.Fprintln(w, "  cmuxd-remote cli <command> [args...]")
 }
 
 func runStdioServer(stdin io.Reader, stdout io.Writer) error {