event: add helper to append user ID to Mentions

event/message.go

@@ -8,6 +8,7 @@ package event
 
 import (
 	"encoding/json"
+	"slices"
 	"strconv"
 	"strings"
 
@@ -212,6 +213,12 @@ type Mentions struct {
 	Room    bool        `json:"room,omitempty"`
 }
 
+func (m *Mentions) Add(userID id.UserID) {
+	if !slices.Contains(m.UserIDs, userID) {
+		m.UserIDs = append(m.UserIDs, userID)
+	}
+}
+
 type EncryptedFileInfo struct {
 	attachment.EncryptedFile
 	URL id.ContentURIString `json:"url"`