component AP gateway: add mention to direct messages:

when a direct (not public) message is sent to AP peer, a mention should be present
otherwise the peer won't receive a notification in most AP implementation (notably
Mastodon).

sat/plugins/plugin_comp_ap_gateway/__init__.py

@@ -2225,7 +2225,16 @@ class APGateway:
             mb_data["id"] = origin_id
         client = self.client.getVirtualClient(mess_data["from"])
         ap_item = await self.mb_data_2_ap_item(client, mb_data, public=False)
-        ap_item["object"]["to"] = ap_item["to"] = [actor_id]
+        ap_object = ap_item["object"]
+        ap_object["to"] = ap_item["to"] = [actor_id]
+        # we add a mention to direct message, otherwise peer is not notified in some AP
+        # implementations (notably Mastodon), and the message may be missed easily.
+        ap_object.setdefault("tag", []).append({
+            "type": TYPE_MENTION,
+            "href": actor_id,
+            "name": f"@{actor_account}",
+        })
+
         await self.signAndPost(inbox, ap_item["actor"], ap_item)
         return mess_data