Bare run in a terminal prints the help screen; add -h/--help

A zero-argument invocation now shows the usage text when stdout is a
console (double-clicked exe, interactive shell). Without a terminal —
Docker entrypoint, services, pipes — a bare invocation still starts the
proxy, so the container image and service behavior are unchanged.

README.md

@@ -91,9 +91,13 @@ override file values. Invalid values fail at startup.
 
 ```sh
 go build ./cmd/gpu-turnstile
-./gpu-turnstile
+OLLAMA_URL=http://127.0.0.1:11435 COMFY_URL=http://127.0.0.1:8189 ./gpu-turnstile
 ```
 
+Running the binary with no arguments in a terminal prints the help screen
+(same as `-h`/`--help`); without a terminal (services, containers) a bare
+invocation starts the proxy.
+
 ### Run natively on Windows (current primary deployment)
 
 Download `gpu-turnstile.exe` from a release and install it as a Windows

cmd/gpu-turnstile/main.go

@@ -35,8 +35,74 @@ var version = "dev"
 // process: a signed update has been staged and the GPU lock is idle.
 const exitCodeUpdate = 3
 
+// stdoutIsTerminal reports whether stdout is a console (char device), as
+// opposed to a pipe or file — which is what Docker containers and services
+// see.
+func stdoutIsTerminal() bool {
+	fi, err := os.Stdout.Stat()
+	return err == nil && fi.Mode()&os.ModeCharDevice != 0
+}
+
+// parseFlags extracts -config <path> (or -config=<path>), the
+// --install-service / --remove-service switches, --no-copy, -h/--help and
+// the hidden --elevated-child marker from args.
+func parseFlags(args []string) (configPath string, install, remove, noCopy, help, elevatedChild bool, rest []string) {
+	rest = args[:0]
+	for i := 0; i < len(args); i++ {
+		switch {
+		case args[i] == "-config" && i+1 < len(args):
+			configPath = args[i+1]
+			i++
+		case strings.HasPrefix(args[i], "-config="):
+			configPath = strings.TrimPrefix(args[i], "-config=")
+		case args[i] == "--install-service" || args[i] == "-install-service":
+			install = true
+		case args[i] == "--remove-service" || args[i] == "-remove-service":
+			remove = true
+		case args[i] == "--no-copy" || args[i] == "-no-copy":
+			noCopy = true
+		case args[i] == "-h" || args[i] == "--help" || args[i] == "-help":
+			help = true
+		case args[i] == "--elevated-child":
+			elevatedChild = true
+		default:
+			rest = append(rest, args[i])
+		}
+	}
+	return configPath, install, remove, noCopy, help, elevatedChild, rest
+}
+
+const usageText = `gpu-turnstile — GPU arbitration proxy for Ollama + ComfyUI
+
+Usage:
+  gpu-turnstile -config <path>                                run the proxy
+  gpu-turnstile --install-service [--no-copy] [-config path]  install + start as a service
+  gpu-turnstile --remove-service                              stop + uninstall the service
+  gpu-turnstile -h | --help                                   this help
+
+Options:
+  -config <path>      config file (default: gpu-turnstile.env next to the exe)
+  --install-service   copies the binary into the canonical location
+                      (%ProgramFiles%\gpu-turnstile or /var/lib/gpu-turnstile)
+                      unless --no-copy; on Windows a UAC prompt appears when
+                      the shell is not elevated
+  --no-copy           with --install-service: register the current location as-is
+
+All runtime settings are environment variables or KEY=VALUE lines in the
+config file (OLLAMA_URL, COMFY_URL, LOGLEVEL, ...); see README.md.
+`
+
 func main() {
-	configPath, install, remove, noCopy, elevatedChild, args := parseFlags(os.Args[1:])
+	configPath, install, remove, noCopy, help, elevatedChild, args := parseFlags(os.Args[1:])
+	bare := configPath == "" && !install && !remove && !elevatedChild && len(args) == 0
+	if help || (bare && stdoutIsTerminal()) {
+		// Bare invocation in a terminal (e.g. double-clicked on Windows)
+		// shows the help instead of starting a proxy window with no visible
+		// explanation. Without a terminal — Docker containers, services,
+		// pipes — a bare invocation starts the proxy as before.
+		fmt.Print(usageText)
+		return
+	}
 	if len(args) > 0 && args[0] == "service" {
 		// Legacy subcommand form: gpu-turnstile service install|remove.
 		if len(args) != 2 || (args[1] != "install" && args[1] != "remove") {
@@ -89,33 +155,6 @@ func main() {
 	}
 }
 
-// parseFlags extracts -config <path> (or -config=<path>), the
-// --install-service / --remove-service switches, --no-copy and the hidden
-// --elevated-child marker from args.
-func parseFlags(args []string) (configPath string, install, remove, noCopy, elevatedChild bool, rest []string) {
-	rest = args[:0]
-	for i := 0; i < len(args); i++ {
-		switch {
-		case args[i] == "-config" && i+1 < len(args):
-			configPath = args[i+1]
-			i++
-		case strings.HasPrefix(args[i], "-config="):
-			configPath = strings.TrimPrefix(args[i], "-config=")
-		case args[i] == "--install-service" || args[i] == "-install-service":
-			install = true
-		case args[i] == "--remove-service" || args[i] == "-remove-service":
-			remove = true
-		case args[i] == "--no-copy" || args[i] == "-no-copy":
-			noCopy = true
-		case args[i] == "--elevated-child":
-			elevatedChild = true
-		default:
-			rest = append(rest, args[i])
-		}
-	}
-	return configPath, install, remove, noCopy, elevatedChild, rest
-}
-
 // defaultConfigPath returns gpu-turnstile.env next to the executable.
 func defaultConfigPath() string {
 	exe, err := os.Executable()