fix: synchronize logs, buffer events channel, exit on goroutine failure

- Add mutex to prevent interleaved log output from concurrent goroutines
- Make logMsg delegate to logPrintf for consistent synchronization
- Buffer events channel to size 1 with select/drop when full
- Close events channel on ListenForTrainer exit so process terminates

cmd/bridge/ant.go

@@ -28,6 +28,8 @@ func resetAndWait(drv io.ReadWriter) error {
 
 func ListenForTrainer(vendorId uint16, productId uint16, deviceNumber uint32,
 	events chan<- Event) {
+	defer close(events)
+
 	drv, err := usb.GetDevice(gousb.ID(vendorId), gousb.ID(productId))
 	if err != nil {
 		panic(err)
@@ -66,9 +68,13 @@ func ListenForTrainer(vendorId uint16, productId uint16, deviceNumber uint32,
 			cur := ant.PowerMessage(msg)
 			logPrintf("ant: %v: power: %dW  cadence: %d rpm\n",
 				msg.DeviceNumber(), cur.InstantaneousPower(), cur.InstantaneousCadence())
-			events <- Event{
+			select {
+			case events <- Event{
 				Power:   cur.InstantaneousPower(),
 				Cadence: cur.InstantaneousCadence(),
+			}:
+			default:
+				logPrintf("ant: dropped event, buffer full\n")
 			}
 		}
 	}

cmd/bridge/cli.go

@@ -73,7 +73,7 @@ This allows these trainers to be used with modern devices that don't support ANT
 				logPrintf("hciconfig up failed: %v\n", err)
 			}
 
-			events := make(chan Event)
+			events := make(chan Event, 1)
 			go ListenForTrainer(uint16(c.vendorID), uint16(c.productID), c.deviceNumber, events)
 			ExposeBluetooth(events)
 

cmd/bridge/log.go

@@ -2,15 +2,20 @@ package main
 
 import (
 	"fmt"
+	"sync"
 	"time"
 )
 
+var logMu sync.Mutex
+
 func logMsg(msg string) {
-	fmt.Println(time.Now().Format("2006-01-02 15:04:05") + " " + msg)
+	logPrintf("%s\n", msg)
 }
 
 func logPrintf(format string, a ...any) {
+	logMu.Lock()
 	fmt.Printf(time.Now().Format("2006-01-02 15:04:05")+" "+format, a...)
+	logMu.Unlock()
 }
 
 func logMsgf(format string, a ...any) {