feat(go): publish realtime fields stream

go/vehicle-gateway/internal/realtime/kv.go

@@ -22,6 +22,51 @@ type RealtimeKVField struct {
 	EventID      string
 }
 
+func BuildFieldsEnvelope(env envelope.FrameEnvelope) (envelope.FrameEnvelope, bool) {
+	if !envelope.IsRealtimeTelemetryFrame(env) {
+		return envelope.FrameEnvelope{}, false
+	}
+	rows := realtimeKVFields(env, env.Parsed)
+	fields := make(map[string]any, len(rows)+len(env.Fields))
+	for _, row := range rows {
+		key := row.Domain
+		if strings.TrimSpace(row.Field) != "" {
+			key += "." + row.Field
+		}
+		fields[key] = row.Value
+	}
+	for key, value := range env.Fields {
+		if strings.TrimSpace(key) != "" {
+			fields[key] = value
+		}
+	}
+	if len(fields) == 0 {
+		return envelope.FrameEnvelope{}, false
+	}
+	out := envelope.FrameEnvelope{
+		EventID:        env.StableEventID() + ":fields",
+		TraceID:        env.TraceID,
+		Protocol:       env.Protocol,
+		MessageID:      env.MessageID,
+		Sequence:       env.Sequence,
+		VIN:            env.VIN,
+		VehicleKeyHint: env.VehicleKeyHint,
+		Phone:          env.Phone,
+		DeviceID:       env.DeviceID,
+		Plate:          env.Plate,
+		SourceEndpoint: env.SourceEndpoint,
+		EventTimeMS:    env.EventTimeMS,
+		ReceivedAtMS:   env.ReceivedAtMS,
+		Fields:         fields,
+		Parsed: map[string]any{
+			"source_event_id": env.StableEventID(),
+			"field_mapping":   realtimeFieldMappingVersion,
+		},
+		ParseStatus: envelope.ParseOK,
+	}
+	return out, true
+}
+
 type protocolFieldMapping struct {
 	Prefix       string
 	GBDataUnits  bool