maybeDaemonize re-executes the process detached from the controlling terminal so the user can close the launching shell once the tray icon

cmd/iptw/daemon_unix.go

@@ -0,0 +1,55 @@
+//go:build !windows
+
+package main
+
+import (
+	"os"
+	"os/exec"
+	"syscall"
+)
+
+// maybeDaemonize re-executes the process detached from the controlling
+// terminal so the user can close the launching shell once the tray icon
+// appears.  It is a no-op when --foreground is passed.
+//
+// How it works:
+//  1. The original (parent) process re-execs itself with all the same
+//     arguments plus "--foreground", using Setsid=true so the child gets a
+//     new session and is no longer attached to the terminal.
+//  2. The parent then exits with code 0, freeing the terminal.
+//  3. The child (which has --foreground set) skips this function and runs
+//     the application normally.
+func maybeDaemonize(foreground bool) {
+	if foreground {
+		return
+	}
+
+	exe, err := os.Executable()
+	if err != nil {
+		// Cannot determine the executable path; just run in the foreground.
+		return
+	}
+
+	// Forward every original argument and add --foreground so the child does
+	// not daemonize again.
+	args := make([]string, 0, len(os.Args)-1+1)
+	args = append(args, os.Args[1:]...)
+	args = append(args, "--foreground")
+
+	cmd := exec.Command(exe, args...)
+	cmd.SysProcAttr = &syscall.SysProcAttr{Setsid: true}
+	// Disconnect all standard streams so the child has no reference to the
+	// parent terminal.
+	cmd.Stdin = nil
+	cmd.Stdout = nil
+	cmd.Stderr = nil
+
+	if err := cmd.Start(); err != nil {
+		// If we cannot spawn the background child, fall through and run
+		// normally in the foreground rather than failing silently.
+		return
+	}
+
+	// Parent exits, releasing the terminal.
+	os.Exit(0)
+}

cmd/iptw/daemon_windows.go

@@ -0,0 +1,7 @@
+//go:build windows
+
+package main
+
+// maybeDaemonize is a no-op on Windows.  Binaries built with -H windowsgui
+// already have no console window, so there is nothing to detach from.
+func maybeDaemonize(_ bool) {}

cmd/iptw/main.go

@@ -23,8 +23,10 @@ var (
 func main() {
 	var forceStart bool
 	var showVersion bool
+	var foreground bool
 	flag.BoolVar(&forceStart, "force", false, "Force start even if another instance appears to be running")
 	flag.BoolVar(&showVersion, "version", false, "Show version information")
+	flag.BoolVar(&foreground, "foreground", false, "Run in the foreground (keep terminal attached)")
 	flag.Parse()
 
 	// Handle version request
@@ -35,6 +37,11 @@ func main() {
 		return
 	}
 
+	// On macOS/Linux: detach from the terminal so the user can close the
+	// launching shell.  The process re-execs itself with --foreground and
+	// the parent exits immediately.  This is a no-op on Windows.
+	maybeDaemonize(foreground)
+
 	// On Windows GUI builds, set up file logging immediately so that any
 	// startup failure is recorded even before the config is read.
 	if closer := logging.SetupWindowsFileLogger(slog.LevelDebug); closer != nil {