feat: replies to comments

A comment can answer another one (replyTo), one level deep: answering a
reply joins the same thread, and it must be on the same ticket. Whoever
wrote the comment gets a new REPLIED notification, and the activity says
"respondió a un comentario".

A comment deleted while it has replies stays, without its text
(deleted: true), so the thread still reads; it goes with its last reply
and does not count in commentCount.

The ticket page shows threads with their replies indented and a
"Responder" box; REST, GraphQL and the MCP (add_comment, get_issue) take
and show replyTo. Existing comments are unchanged. Docs, Word and PDF
updated.

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

libs/api/tracker/domain/src/lib/comment/comment.ts

@@ -15,6 +15,12 @@ export interface CommentProps {
   projectId: string;
   authorId: string;
   body: string;
+  /**
+   * The comment this one answers; always a top-level one (one level of
+   * replies). Null for a top-level comment, and on comments made before
+   * there were replies.
+   */
+  replyTo: string | null;
   deleted: boolean;
   createdAt: string;
   editedAt: string | null;
@@ -22,12 +28,13 @@ export interface CommentProps {
 
 const MAX_BODY = 20_000;
 
-/** Decisions and explanations inside a ticket. */
+/** Decisions and explanations inside a ticket, and the replies to them. */
 export class Comment extends VersionedAggregateRoot implements CommentProps {
   public issueId!: string;
   public projectId!: string;
   public authorId!: string;
   public body!: string;
+  public replyTo: string | null = null;
   public deleted = false;
   public createdAt!: string;
   public editedAt: string | null = null;

libs/api/tracker/domain/src/lib/factories/comment.factory.ts

@@ -10,6 +10,8 @@ export class CommentFactory {
     projectId: string;
     authorId: string;
     body: string;
+    /** Top-level comment it answers. */
+    replyTo?: string | null;
   }): Comment {
     const data: CommentProps = {
       id: newId(),
@@ -17,6 +19,7 @@ export class CommentFactory {
       projectId: props.projectId,
       authorId: props.authorId,
       body: validCommentBody(props.body),
+      replyTo: props.replyTo ?? null,
       deleted: false,
       createdAt: new Date().toISOString(),
       editedAt: null,

libs/api/tracker/domain/src/lib/read-models/comment.read-model.ts

@@ -6,6 +6,13 @@ export class CommentReadModel {
   projectId!: string;
   author!: UserRefReadModel;
   body!: string;
+  /** Top-level comment it answers; null for a top-level one. */
+  replyTo!: string | null;
+  /**
+   * Deleted while it had replies: kept, without its text, so the
+   * conversation under it still makes sense. Gone with its last reply.
+   */
+  deleted!: boolean;
   createdAt!: string;
   editedAt!: string | null;
   version!: number;

libs/api/tracker/domain/src/lib/read-models/notification.read-model.ts

@@ -12,6 +12,8 @@ export enum NotificationKind {
   COMMENTED = 'COMMENTED',
   /** Someone wrote @you. */
   MENTIONED = 'MENTIONED',
+  /** Someone answered a comment of yours. */
+  REPLIED = 'REPLIED',
   /** A ticket you follow changed. */
   WATCHED = 'WATCHED',
   /** You were added to a project. */