feat: mentions and following tickets

Mention project members in comments with @, follow and unfollow tickets,
and get told when something changes on the tickets you follow. Commenting
on a ticket starts following it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libs/api/tracker/application/src/lib/notifications/notifications.event-handler.ts

@@ -4,10 +4,12 @@ import {
   IssueAssignedEvent,
   IssueCreatedEvent,
   IssueStatusChangedEvent,
+  mentionedUserIds,
   NotificationKind,
   ProjectMemberAddedEvent,
   StatusCategory,
   TrackerEvent,
+  withoutMentionMarkup,
 } from '@task-stream/api/tracker/domain';
 import { FindIssuesRepository } from '../ports/find-issues.repository';
 import { FindProjectsRepository } from '../ports/find-projects.repository';
@@ -17,14 +19,16 @@ import { NotificationDraft, Notifier } from './notifier';
 /* Read by people, like the activity feed: Spanish. */
 
 const excerpt = (text: string, max = 120) => {
-  const flat = text.replace(/\s+/g, ' ').trim();
+  const flat = withoutMentionMarkup(text).replace(/\s+/g, ' ').trim();
   return flat.length > max ? `${flat.slice(0, max - 1)}…` : flat;
 };
 
 /**
  * Who is told what, for the events that concern someone in particular:
- * whoever a ticket is assigned to, whoever reported or works on it when it
- * moves or gets a comment, whoever joins a project.
+ * whoever is mentioned, whoever a ticket is assigned to, whoever reported or
+ * works on it when it moves or gets a comment, whoever follows it, whoever
+ * joins a project. The order is the order of importance: each person gets
+ * one notification per event, for the first reason that applies.
  */
 @EventsHandler(
   IssueCreatedEvent,
@@ -81,6 +85,9 @@ export class NotificationsEventHandler implements IEventHandler<TrackerEvent> {
     const assigneeId =
       'assigneeId' in issue ? issue.assigneeId : (issue.assignee?.id ?? null);
     const ticket = `${issue.key}: ${issue.title}`;
+    const watcherIds =
+      'watchers' in issue ? issue.watchers.map((w) => w.id) : [];
+    const memberIds = new Set(project.members.map((m) => m.user.id));
 
     const drafts: NotificationDraft[] = [];
     if (event instanceof IssueCreatedEvent && assigneeId) {
@@ -90,12 +97,26 @@ export class NotificationsEventHandler implements IEventHandler<TrackerEvent> {
         summary: `${actor} te asignó ${ticket}`,
       });
     }
-    if (event instanceof IssueAssignedEvent && event.assigneeId) {
-      drafts.push({
-        userId: event.assigneeId,
-        kind: NotificationKind.ASSIGNED,
-        summary: `${actor} te asignó ${ticket}`,
-      });
+    if (event instanceof IssueAssignedEvent) {
+      const assignee = event.assigneeId
+        ? (await this.users.refs([event.assigneeId])).of(event.assigneeId).name
+        : null;
+      if (event.assigneeId) {
+        drafts.push({
+          userId: event.assigneeId,
+          kind: NotificationKind.ASSIGNED,
+          summary: `${actor} te asignó ${ticket}`,
+        });
+      }
+      for (const userId of watcherIds) {
+        drafts.push({
+          userId,
+          kind: NotificationKind.WATCHED,
+          summary: assignee
+            ? `${actor} asignó ${ticket} a ${assignee}`
+            : `${actor} dejó sin asignar ${ticket}`,
+        });
+      }
     }
     if (event instanceof IssueStatusChangedEvent) {
       const to = event.meta?.toName ?? event.to;
@@ -105,6 +126,9 @@ export class NotificationsEventHandler implements IEventHandler<TrackerEvent> {
         event.meta?.toCategory !== StatusCategory.QA &&
         event.meta?.toCategory !== StatusCategory.DONE;
       const reason = event.reason ? `: ${excerpt(event.reason)}` : '';
+      const summary = failedQa
+        ? `${actor} devolvió ${ticket} desde QA${reason}`
+        : `${actor} movió ${ticket} a ${to}${reason}`;
       for (const userId of [assigneeId, reporterId]) {
         if (!userId) continue;
         drafts.push({
@@ -112,19 +136,37 @@ export class NotificationsEventHandler implements IEventHandler<TrackerEvent> {
           kind: failedQa
             ? NotificationKind.QA_FAILED
             : NotificationKind.STATUS_CHANGED,
-          summary: failedQa
-            ? `${actor} devolvió ${ticket} desde QA${reason}`
-            : `${actor} movió ${ticket} a ${to}${reason}`,
+          summary,
         });
       }
+      for (const userId of watcherIds) {
+        drafts.push({ userId, kind: NotificationKind.WATCHED, summary });
+      }
     }
     if (event instanceof CommentAddedEvent) {
+      const said = `«${excerpt(event.comment.body)}»`;
+      // Only members: a mention cannot reach someone who cannot read the ticket.
+      for (const userId of mentionedUserIds(event.comment.body)) {
+        if (!memberIds.has(userId)) continue;
+        drafts.push({
+          userId,
+          kind: NotificationKind.MENTIONED,
+          summary: `${actor} te mencionó en ${issue.key}: ${said}`,
+        });
+      }
       for (const userId of [assigneeId, reporterId]) {
         if (!userId) continue;
         drafts.push({
           userId,
           kind: NotificationKind.COMMENTED,
-          summary: `${actor} comentó en ${issue.key}: «${excerpt(event.comment.body)}»`,
+          summary: `${actor} comentó en ${issue.key}: ${said}`,
+        });
+      }
+      for (const userId of watcherIds) {
+        drafts.push({
+          userId,
+          kind: NotificationKind.WATCHED,
+          summary: `${actor} comentó en ${issue.key}, que sigues: ${said}`,
         });
       }
     }