diff --git a/internal/runner/api/jobconn.go b/internal/runner/api/jobconn.go
index ee3fbbf..5b72cc1 100644
--- a/internal/runner/api/jobconn.go
+++ b/internal/runner/api/jobconn.go
@@ -18,6 +18,7 @@ type JobConnection struct {
 	writeMu       sync.Mutex
 	stopPing      chan struct{}
 	stopHeartbeat chan struct{}
+	stopOnce      sync.Once
 	isConnected   bool
 	connMu        sync.RWMutex
 }
@@ -132,13 +133,12 @@ func (j *JobConnection) pingLoop() {
 
 // Heartbeat sends a heartbeat message over WebSocket to keep runner online.
 func (j *JobConnection) Heartbeat() {
+	j.writeMu.Lock()
+	defer j.writeMu.Unlock()
 	if j.conn == nil {
 		return
 	}
 
-	j.writeMu.Lock()
-	defer j.writeMu.Unlock()
-
 	msg := map[string]interface{}{
 		"type":      "runner_heartbeat",
 		"timestamp": time.Now().Unix(),
@@ -178,27 +178,34 @@ func (j *JobConnection) heartbeatLoop() {
 	}
 }
 
+// stopLoops signals ping/heartbeat goroutines to exit.
+// Channels are closed once and left non-nil so loops can receive without racing Close.
+func (j *JobConnection) stopLoops() {
+	j.stopOnce.Do(func() {
+		if j.stopHeartbeat != nil {
+			close(j.stopHeartbeat)
+		}
+		if j.stopPing != nil {
+			close(j.stopPing)
+		}
+	})
+}
+
 // Close closes the WebSocket connection.
 func (j *JobConnection) Close() {
+	j.stopLoops()
+
+	j.writeMu.Lock()
+	defer j.writeMu.Unlock()
+
 	j.connMu.Lock()
 	j.isConnected = false
+	conn := j.conn
+	j.conn = nil
 	j.connMu.Unlock()
 
-	// Stop heartbeat goroutine
-	if j.stopHeartbeat != nil {
-		close(j.stopHeartbeat)
-		j.stopHeartbeat = nil
-	}
-
-	// Stop ping goroutine
-	if j.stopPing != nil {
-		close(j.stopPing)
-		j.stopPing = nil
-	}
-
-	if j.conn != nil {
-		j.conn.Close()
-		j.conn = nil
+	if conn != nil {
+		conn.Close()
 	}
 }
 
@@ -211,13 +218,12 @@ func (j *JobConnection) IsConnected() bool {
 
 // Log sends a log entry to the manager.
 func (j *JobConnection) Log(taskID int64, level types.LogLevel, message string) {
+	j.writeMu.Lock()
+	defer j.writeMu.Unlock()
 	if j.conn == nil {
 		return
 	}
 
-	j.writeMu.Lock()
-	defer j.writeMu.Unlock()
-
 	msg := map[string]interface{}{
 		"type": "log_entry",
 		"data": map[string]interface{}{
@@ -242,13 +248,12 @@ func (j *JobConnection) Log(taskID int64, level types.LogLevel, message string)
 
 // Progress sends a progress update to the manager.
 func (j *JobConnection) Progress(taskID int64, progress float64) {
+	j.writeMu.Lock()
+	defer j.writeMu.Unlock()
 	if j.conn == nil {
 		return
 	}
 
-	j.writeMu.Lock()
-	defer j.writeMu.Unlock()
-
 	msg := map[string]interface{}{
 		"type": "progress",
 		"data": map[string]interface{}{
@@ -272,13 +277,12 @@ func (j *JobConnection) Progress(taskID int64, progress float64) {
 
 // OutputUploaded notifies that an output file was uploaded.
 func (j *JobConnection) OutputUploaded(taskID int64, fileName string) {
+	j.writeMu.Lock()
+	defer j.writeMu.Unlock()
 	if j.conn == nil {
 		return
 	}
 
-	j.writeMu.Lock()
-	defer j.writeMu.Unlock()
-
 	msg := map[string]interface{}{
 		"type": "output_uploaded",
 		"data": map[string]interface{}{
@@ -307,14 +311,13 @@ func (j *JobConnection) OutputUploaded(taskID int64, fileName string) {
 // freeRequeue asks the manager to requeue a failure without incrementing retry_count
 // (used when this attempt newly armed GPU lockout).
 func (j *JobConnection) Complete(taskID int64, success bool, errorMsg error, freeRequeue bool) {
+	j.writeMu.Lock()
+	defer j.writeMu.Unlock()
 	if j.conn == nil {
 		log.Printf("Cannot send task complete: WebSocket connection is nil")
 		return
 	}
 
-	j.writeMu.Lock()
-	defer j.writeMu.Unlock()
-
 	data := map[string]interface{}{
 		"task_id": taskID,
 		"success": success,