feat(guild): <@id> mention mechanism

- parse <@user-id> outside backtick spans
- general: message with an at-list wakes only the at'd users (else all)
- report/triage/custom: mentions change nothing
- discuss/work: mention by current speaker pushes a sub-rotation frame
  (atList = mentions - sender, intersected with channel members); single
  linear pass (real/no-reply/force-proceed), then pop back to the saved
  parent pointer (resumes at the pusher); nested frames supported

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/realtime/realtime.gateway.ts

@@ -18,18 +18,24 @@ type XType = 'general' | 'work' | 'report' | 'discuss' | 'triage' | 'custom';
 // Precedence:
 //  1. the author never gets woken by their own message
 //  2. triage/custom: only wake users in the channel's wake_mapping
-//  3. general: wake everyone
+//     (mentions change nothing here)
+//  3. general: if the message has an at-list, wake only the at'd users;
+//     otherwise wake everyone
 //  4. report (and anything else): wake nobody
 export function computeWakeup(args: {
   xType: XType;
   recipientUserId: string;
   authorUserId: string;
   wakeUserIds: Set<string>;
+  mentionUserIds?: Set<string>;
 }): boolean {
-  const { xType, recipientUserId, authorUserId, wakeUserIds } = args;
+  const { xType, recipientUserId, authorUserId, wakeUserIds, mentionUserIds } = args;
   if (recipientUserId === authorUserId) return false;
   switch (xType) {
     case 'general':
+      if (mentionUserIds && mentionUserIds.size > 0) {
+        return mentionUserIds.has(recipientUserId);
+      }
       return true;
     case 'triage':
     case 'custom':
@@ -166,7 +172,12 @@ export class RealtimeGateway implements OnGatewayConnection, OnGatewayDisconnect
   async emitMessageCreated(
     channelId: string,
     data: Record<string, unknown>,
-    ctx: { xType: XType; authorUserId: string; wakeUserIds: Set<string> },
+    ctx: {
+      xType: XType;
+      authorUserId: string;
+      wakeUserIds: Set<string>;
+      mentionUserIds?: Set<string>;
+    },
   ): Promise<void> {
     const sockets = await this.server.in(`channel:${channelId}`).fetchSockets();
     for (const s of sockets) {
@@ -176,6 +187,7 @@ export class RealtimeGateway implements OnGatewayConnection, OnGatewayDisconnect
         recipientUserId,
         authorUserId: ctx.authorUserId,
         wakeUserIds: ctx.wakeUserIds,
+        mentionUserIds: ctx.mentionUserIds,
       });
       s.emit('message.created', { ...data, wakeup });
     }