add a tone test mode that bypasses the soundcard

Add -tone-test to transmit a generated 440 Hz Opus tone and save
incoming audio to the file named by -tone-out.
Diagnosing an audio problem previously required a working capture and
playback device, which is exactly what is in question. This mode opens
no OpenAL device at all, so the network and codec path can be tested
on a machine with no sound hardware.

Open the capture file before starting the generator.
Starting transmission first left a tone goroutine running with nowhere
to write when the path was unusable.

Refuse file playback while in tone test mode, and ignore the
microphone volume keys.
Both operate on a stream that does not exist here.

Stop the generator and detach the file saver on disconnect.
A reconnect otherwise attached a second saver to the same file.

Add -auto-transmit to key the microphone as soon as the connection is
up.
Useful for a bot or a monitoring client that should never need a
keypress. It runs from both the connect event and the point where the
audio stream is created, because the server's welcome arrives before
the stream exists.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

main.go

@@ -88,6 +88,9 @@ func main() {
 	jitterBuffer := flag.Int("jitter-buffer", 40, "incoming per-user audio buffer in ms (0, 20, 40, or 60)")
 	profile := flag.Bool("profile", false, "add http server to serve profiles")
 	noiseSuppressionEnabled := flag.Bool("noise-suppression", false, "enable noise suppression for microphone input")
+	autoTransmit := flag.Bool("auto-transmit", false, "start transmitting immediately on connect")
+	toneTest := flag.Bool("tone-test", false, "send a 440 Hz test tone instead of microphone (bypasses soundcard)")
+	toneTestOutput := flag.String("tone-out", "incoming.pcm", "file to save incoming audio to in tone-test mode")
 	tcpOnly := flag.Bool("tcp", false, "disable UDP, force audio through TCP tunnel")
 	logLevel := flag.String("log", "warn", "log level: debug, info, warn, error")
 	logFile := flag.String("logfile", "", "write logs to this file (logging is disabled when omitted)")
@@ -194,6 +197,9 @@ func main() {
 		Config:          gumble.NewConfig(),
 		UserConfig:      userConfig,
 		Address:         *server,
+		AutoTransmit:    *autoTransmit,
+		ToneTest:        *toneTest,
+		ToneTestOutput:  *toneTestOutput,
 		MutedChannels:   make(map[uint32]bool),
 		NoiseSuppressor: noise.NewSuppressor(),
 	}