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/presenters/src/lib/graphql/issue.resolver.ts

@@ -183,6 +183,25 @@ export class IssueResolver {
     );
   }
 
+  @Mutation(() => CommandResultGql, {
+    description:
+      'Follow a ticket: be told when it moves, is reassigned or gets a comment',
+  })
+  watchIssue(
+    @CurrentUser() me: User,
+    @Args('issueId', { type: () => ID }) issueId: string,
+  ) {
+    return this.issuesService.watch(me.id, issueId, true);
+  }
+
+  @Mutation(() => CommandResultGql, { description: 'Stop following a ticket' })
+  unwatchIssue(
+    @CurrentUser() me: User,
+    @Args('issueId', { type: () => ID }) issueId: string,
+  ) {
+    return this.issuesService.watch(me.id, issueId, false);
+  }
+
   @Mutation(() => CommandResultGql, {
     description:
       'Remove a file from a ticket (whoever uploaded it, or an owner/admin). Upload with the REST API.',

libs/api/tracker/presenters/src/lib/graphql/types.ts

@@ -143,6 +143,8 @@ export class IssueGql {
   @Field(() => String, { nullable: true }) dueDate!: string | null;
   @Field(() => [IssueLinkGql]) links!: IssueLinkGql[];
   @Field(() => [AttachmentGql]) attachments!: AttachmentGql[];
+  @Field(() => [UserRefGql], { description: 'People following the ticket' })
+  watchers!: UserRefGql[];
   @Field(() => Int) commentCount!: number;
   @Field() createdAt!: string;
   @Field() updatedAt!: string;

libs/api/tracker/presenters/src/lib/http/dto/responses.dto.ts

@@ -159,6 +159,8 @@ export class IssueDto {
   dueDate!: string | null;
   @ApiProperty({ type: [IssueLinkDto] }) links!: IssueLinkDto[];
   @ApiProperty({ type: [AttachmentDto] }) attachments!: AttachmentDto[];
+  @ApiProperty({ type: [UserRefDto], description: 'People following it' })
+  watchers!: UserRefDto[];
   @ApiProperty() commentCount!: number;
   @ApiProperty({ format: 'date-time' }) createdAt!: string;
   @ApiProperty({ format: 'date-time' }) updatedAt!: string;

libs/api/tracker/presenters/src/lib/http/issues.controller.ts

@@ -77,6 +77,36 @@ export class IssuesController {
     private readonly refs: Refs,
   ) {}
 
+  @Put('issues/:issue/watch')
+  @ISSUE
+  @ApiOperation({
+    summary: 'Follow a ticket (members, viewers included)',
+    description:
+      'Followers are told when it moves, is reassigned or gets a comment. Commenting follows it too.',
+  })
+  @ApiOkResponse({ type: CommandResultDto })
+  @ApiCommandErrors()
+  async watch(@CurrentUser() me: User, @Param('issue') issue: string) {
+    return this.issues.watch(
+      me.id,
+      await this.refs.issueId(me.id, issue),
+      true,
+    );
+  }
+
+  @Delete('issues/:issue/watch')
+  @ISSUE
+  @ApiOperation({ summary: 'Stop following a ticket' })
+  @ApiOkResponse({ type: CommandResultDto })
+  @ApiCommandErrors()
+  async unwatch(@CurrentUser() me: User, @Param('issue') issue: string) {
+    return this.issues.watch(
+      me.id,
+      await this.refs.issueId(me.id, issue),
+      false,
+    );
+  }
+
   @Get('me/issues')
   @ApiOperation({
     summary: 'My work: tickets across all my projects',