fix: explicit m.mentions for ticket notifications and roasts (ahead of Synapse 1.164)

Synapse 1.164 turns on MSC4210 by default: the legacy push rules that
pinged when a user ID or display name appeared in the body are removed, so
a message only notifies the users listed in m.mentions.

- hookshot/tinker-tickets.js deliberately pings assignees/watchers
  (notify_users) with matrix.to links; those pings would stop. Return
  mentions: { user_ids: notifyUsers } (hookshot 7.3.2 v2 transforms
  support it).
- matrixbot: send_html takes optional mention_user_ids; !roast mentions the
  target when given as a full Matrix ID. Winner announcements stay without
  a ping (the player is already in the room).

No @room is sent anywhere. Lotus Chat already sends m.mentions.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017PCb59uY3UKqDqt7B6hzd5

matrixbot/commands.py

@@ -2273,7 +2273,9 @@ async def cmd_roast(client: AsyncClient, room_id: str, sender: str, args: str):
         f'<blockquote>{roast}</blockquote>'
         f'<sup><em>via {_model_label(CREATIVE_MODEL)}</em></sup>'
     )
-    await send_html(client, room_id, plain, html)
+    # Ping the person being roasted when they were named by Matrix ID.
+    target_id = target_raw if re.fullmatch(r"@[^\s:]+:[^\s]+", target_raw) else None
+    await send_html(client, room_id, plain, html, mention_user_ids=[target_id] if target_id else None)
 
 
 # ---------------------------------------------------------------------------

matrixbot/utils.py

@@ -70,17 +70,25 @@ async def send_text(client: AsyncClient, room_id: str, text: str):
     return resp
 
 
-async def send_html(client: AsyncClient, room_id: str, plain: str, html: str):
+async def send_html(
+    client: AsyncClient, room_id: str, plain: str, html: str, mention_user_ids: list[str] | None = None
+):
     logger = logging.getLogger("matrixbot")
+    content = {
+        "msgtype": "m.text",
+        "body": plain,
+        "format": "org.matrix.custom.html",
+        "formatted_body": html,
+    }
+    # Explicit mentions (m.mentions). From Synapse 1.164 a name or user ID in
+    # the body no longer pings anyone (MSC4210), so a message that should
+    # notify someone has to say so.
+    if mention_user_ids:
+        content["m.mentions"] = {"user_ids": mention_user_ids}
     resp = await _room_send_trusted(
         client, room_id,
         message_type="m.room.message",
-        content={
-            "msgtype": "m.text",
-            "body": plain,
-            "format": "org.matrix.custom.html",
-            "formatted_body": html,
-        },
+        content=content,
     )
     if not isinstance(resp, RoomSendResponse):
         logger.error("send_html failed: %s", resp)