hub: actually send start/stop commands over MQTT

The /cameras/{id}/start and /stop handlers only wrote a recording_events
row — they never published the command, so the camera never recorded.
Add Subscriber.PublishCommand (publishes {"command":...} to
remoterig/cameras/<id>/command, which the XIAO forwards to the ESP-01S),
thread a CommandPublisher into the recording handlers, and wire mqttSub in
via apiRouter. Tests pass nil (publish skipped).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/api/camera_test.go

@@ -26,8 +26,8 @@ func setupTestRouter(t *testing.T) (*db.DB, chi.Router) {
 	r.Get("/cameras", ListCameras(database))
 	r.Post("/cameras", RegisterCamera(database))
 	r.Get("/cameras/{id}", GetCameraDetail(database))
-	r.Post("/cameras/{id}/start", StartRecording(database))
-	r.Post("/cameras/{id}/stop", StopRecording(database))
+	r.Post("/cameras/{id}/start", StartRecording(database, nil))
+	r.Post("/cameras/{id}/stop", StopRecording(database, nil))
 	r.Post("/cameras/{id}/status", PushStatus(database))
 
 	return database, r

internal/api/recording.go

@@ -9,8 +9,14 @@ import (
 	"github.com/go-chi/chi/v5"
 )
 
+// CommandPublisher sends a command to a camera (implemented by the MQTT
+// subscriber). Nil is allowed (e.g. in tests) — the command is then skipped.
+type CommandPublisher interface {
+	PublishCommand(cameraID, command string) error
+}
+
 // StartRecording returns a handler for POST /cameras/{id}/start.
-func StartRecording(database *db.DB) http.HandlerFunc {
+func StartRecording(database *db.DB, pub CommandPublisher) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		cameraID := chi.URLParam(r, "id")
 		if !validateCameraID(w, cameraID) {
@@ -45,6 +51,15 @@ func StartRecording(database *db.DB) http.HandlerFunc {
 		rowsAffected, _ := result.RowsAffected()
 		log.Printf("Recording started on %s (%d rows affected)", cameraID, rowsAffected)
 
+		// Send the actual command to the camera over MQTT.
+		if pub != nil {
+			if err := pub.PublishCommand(cameraID, "start_recording"); err != nil {
+				log.Printf("Error sending start_recording to %s: %v", cameraID, err)
+				respondError(w, http.StatusBadGateway, "failed to send command to camera", err.Error())
+				return
+			}
+		}
+
 		respondJSON(w, http.StatusOK, map[string]string{
 			"status":    "recording_started",
 			"camera_id": cameraID,
@@ -53,7 +68,7 @@ func StartRecording(database *db.DB) http.HandlerFunc {
 }
 
 // StopRecording returns a handler for POST /cameras/{id}/stop.
-func StopRecording(database *db.DB) http.HandlerFunc {
+func StopRecording(database *db.DB, pub CommandPublisher) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		cameraID := chi.URLParam(r, "id")
 		if !validateCameraID(w, cameraID) {
@@ -88,6 +103,15 @@ func StopRecording(database *db.DB) http.HandlerFunc {
 		rowsAffected, _ := result.RowsAffected()
 		log.Printf("Recording stopped on %s (%d rows affected)", cameraID, rowsAffected)
 
+		// Send the actual command to the camera over MQTT.
+		if pub != nil {
+			if err := pub.PublishCommand(cameraID, "stop_recording"); err != nil {
+				log.Printf("Error sending stop_recording to %s: %v", cameraID, err)
+				respondError(w, http.StatusBadGateway, "failed to send command to camera", err.Error())
+				return
+			}
+		}
+
 		respondJSON(w, http.StatusOK, map[string]string{
 			"status":    "recording_stopped",
 			"camera_id": cameraID,

internal/mqtt/subscriber.go

@@ -143,6 +143,18 @@ type statusPayload struct {
 	UptimeSec         *int    `json:"uptime_sec"`
 }
 
+// PublishCommand sends a command (e.g. "start_recording") to a camera's
+// command topic, which its ESP32 bridge subscribes to and forwards over UART.
+func (s *Subscriber) PublishCommand(cameraID, command string) error {
+	topic := "remoterig/cameras/" + cameraID + "/command"
+	payload, _ := json.Marshal(map[string]string{"command": command})
+	tok := s.client.Publish(topic, 2, false, payload)
+	if !tok.WaitTimeout(3 * time.Second) {
+		return fmt.Errorf("publish to %s timed out", topic)
+	}
+	return tok.Error()
+}
+
 func (s *Subscriber) handleStatus(cameraID string, payload []byte) {
 	var sp statusPayload
 	if err := json.Unmarshal(payload, &sp); err != nil {