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>

apps/api/openapi.json

@@ -4406,7 +4406,7 @@
           "content": {
             "application/json": {
               "schema": {
-                "$ref": "#/components/schemas/CommentBodyDto"
+                "$ref": "#/components/schemas/AddCommentDto"
               }
             }
           }
@@ -4491,7 +4491,7 @@
             "pireon": []
           }
         ],
-        "summary": "Comment on the ticket",
+        "summary": "Comment on the ticket, or answer a comment (replyTo)",
         "tags": [
           "Issues"
         ]
@@ -11423,7 +11423,18 @@
             "$ref": "#/components/schemas/UserRefDto"
           },
           "body": {
-            "type": "string"
+            "type": "string",
+            "description": "Empty on a deleted comment kept for its replies"
+          },
+          "replyTo": {
+            "type": "string",
+            "nullable": true,
+            "format": "uuid",
+            "description": "The top-level comment it answers; null for a top-level one"
+          },
+          "deleted": {
+            "type": "boolean",
+            "description": "Deleted, but kept (without its text) while it has replies"
           },
           "createdAt": {
             "type": "string",
@@ -11443,6 +11454,8 @@
           "issueId",
           "author",
           "body",
+          "replyTo",
+          "deleted",
           "createdAt",
           "editedAt",
           "version"
@@ -11466,13 +11479,18 @@
           "total"
         ]
       },
-      "CommentBodyDto": {
+      "AddCommentDto": {
         "type": "object",
         "properties": {
           "body": {
             "type": "string",
             "example": "Reproducido en Safari 17.",
             "maxLength": 20000
+          },
+          "replyTo": {
+            "type": "string",
+            "format": "uuid",
+            "description": "Comment it answers (one level: answering a reply joins its thread)"
           }
         },
         "required": [
@@ -11497,6 +11515,19 @@
           "file"
         ]
       },
+      "CommentBodyDto": {
+        "type": "object",
+        "properties": {
+          "body": {
+            "type": "string",
+            "example": "Reproducido en Safari 17.",
+            "maxLength": 20000
+          }
+        },
+        "required": [
+          "body"
+        ]
+      },
       "ReleaseStatus": {
         "type": "string",
         "enum": [
@@ -11929,6 +11960,7 @@
           "QA_FAILED",
           "COMMENTED",
           "MENTIONED",
+          "REPLIED",
           "WATCHED",
           "ADDED_TO_PROJECT",
           "REMINDER"

apps/api/schema.gql

@@ -196,11 +196,19 @@ type CommandResult {
 
 type Comment {
   author: UserRef!
+
+  """Empty on a deleted comment kept for its replies"""
   body: String!
   createdAt: String!
+
+  """Deleted, but kept (without its text) while it has replies"""
+  deleted: Boolean!
   editedAt: String
   id: ID!
   issueId: ID!
+
+  """The top-level comment it answers; null for a top-level one"""
+  replyTo: ID
   version: Int!
 }
 
@@ -602,7 +610,11 @@ type Me {
 type Mutation {
   """Add a step to a ticket's checklist"""
   addChecklistItem(input: AddChecklistItemInput!): CommandResult!
-  addComment(body: String!, issueId: ID!): CommandResult!
+
+  """
+  Comment on a ticket, or answer a comment (replyTo; one level of replies)
+  """
+  addComment(body: String!, issueId: ID!, replyTo: ID): CommandResult!
 
   """
   Add a repository with its own secret (the first turns the integration on)
@@ -776,6 +788,7 @@ enum NotificationKind {
   MENTIONED
   QA_FAILED
   REMINDER
+  REPLIED
   STATUS_CHANGED
   WATCHED
 }

apps/mcp/src/app/api/taskstream.schema.ts

@@ -635,7 +635,7 @@ export interface paths {
         /** Comments of the ticket (oldest first) */
         get: operations["IssuesController_listComments"];
         put?: never;
-        /** Comment on the ticket */
+        /** Comment on the ticket, or answer a comment (replyTo) */
         post: operations["IssuesController_addComment"];
         delete?: never;
         options?: never;
@@ -2087,7 +2087,15 @@ export interface components {
             /** Format: uuid */
             issueId: string;
             author: components["schemas"]["UserRefDto"];
+            /** @description Empty on a deleted comment kept for its replies */
             body: string;
+            /**
+             * Format: uuid
+             * @description The top-level comment it answers; null for a top-level one
+             */
+            replyTo: string | null;
+            /** @description Deleted, but kept (without its text) while it has replies */
+            deleted: boolean;
             /** Format: date-time */
             createdAt: string;
             /** Format: date-time */
@@ -2098,9 +2106,14 @@ export interface components {
             items: components["schemas"]["CommentDto"][];
             total: number;
         };
-        CommentBodyDto: {
+        AddCommentDto: {
             /** @example Reproducido en Safari 17. */
             body: string;
+            /**
+             * Format: uuid
+             * @description Comment it answers (one level: answering a reply joins its thread)
+             */
+            replyTo?: string;
         };
         AttachFileDto: {
             /**
@@ -2114,6 +2127,10 @@ export interface components {
              */
             commentId?: string;
         };
+        CommentBodyDto: {
+            /** @example Reproducido en Safari 17. */
+            body: string;
+        };
         /** @enum {string} */
         ReleaseStatus: "PLANNED" | "RELEASED" | "ARCHIVED";
         ReleaseDto: {
@@ -2250,7 +2267,7 @@ export interface components {
             goodFirst: components["schemas"]["ShowcaseIssueDto"][];
         };
         /** @enum {string} */
-        NotificationKind: "ASSIGNED" | "STATUS_CHANGED" | "QA_FAILED" | "COMMENTED" | "MENTIONED" | "WATCHED" | "ADDED_TO_PROJECT" | "REMINDER";
+        NotificationKind: "ASSIGNED" | "STATUS_CHANGED" | "QA_FAILED" | "COMMENTED" | "MENTIONED" | "REPLIED" | "WATCHED" | "ADDED_TO_PROJECT" | "REMINDER";
         NotificationDto: {
             id: string;
             kind: components["schemas"]["NotificationKind"];
@@ -5497,7 +5514,7 @@ export interface operations {
         };
         requestBody: {
             content: {
-                "application/json": components["schemas"]["CommentBodyDto"];
+                "application/json": components["schemas"]["AddCommentDto"];
             };
         };
         responses: {

apps/mcp/src/app/tools/issues.resolver.ts

@@ -224,9 +224,10 @@ export class IssuesResolver {
             )
           ).items.map((c) => ({
             id: c.id,
-            author: c.author.name,
+            replyTo: c.replyTo,
+            author: c.deleted ? null : c.author.name,
             at: c.createdAt,
-            body: c.body,
+            body: c.deleted ? '(deleted; kept for its replies)' : c.body,
           }))
         : undefined;
       const history = params.withHistory
@@ -411,19 +412,27 @@ export class IssuesResolver {
 
   @Tool({
     name: 'add_comment',
-    description: 'Comment on a ticket (decisions, explanations, steps).',
+    description:
+      'Comment on a ticket (decisions, explanations, steps), or answer a comment with replyTo (one level: answering a reply joins its thread).',
     paramsSchema: z.object({
       issue: issueRef,
       body: z.string().min(1).max(20000),
+      replyTo: z
+        .string()
+        .optional()
+        .describe('Id of the comment it answers (see get_issue)'),
     }),
     annotations: WRITE,
   })
-  comment({ issue, body }: { issue: string; body: string }, ctx: McpContext) {
+  comment(
+    { issue, body, replyTo }: { issue: string; body: string; replyTo?: string },
+    ctx: McpContext,
+  ) {
     return toolResult(() =>
       this.api.data(
         this.api.as(ctx).POST('/api/issues/{issue}/comments', {
           params: { path: { issue } },
-          body: { body },
+          body: { body, replyTo },
         }),
       ),
     );

docs/01-vision-general.md

@@ -14,7 +14,7 @@
 | 🚀 Releases          | Versiones a las que se asignan tickets; no se publican con tickets sin terminar (salvo forzando)                                                                          |
 | 📝 Notas de versión  | Borrador en Markdown con los tickets terminados por tipo, editable y copiable, también tras publicar                                                                      |
 | 👥 Asignaciones      | Solo a miembros del proyecto; panel de carga por persona                                                                                                                  |
-| 💬 Comentarios       | Decisiones y explicaciones dentro del ticket, con `@menciones`; el autor edita, el admin modera                                                                           |
+| 💬 Comentarios       | Decisiones y explicaciones dentro del ticket, con respuestas y `@menciones`; el autor edita, el admin modera                                                              |
 | 🔎 Vistas            | El tablero se filtra por texto, persona (o sin asignar), tipo, prioridad, área y release; los filtros se guardan como vistas propias o compartidas con el proyecto        |
 | 🚦 WIP y carriles    | Límite de trabajo en curso por estado (la columna se marca al pasarse) y tablero agrupable por persona, épica, prioridad o tipo                                           |
 | 🎲 Estimación        | Puntos por ticket (escala 0-1-2-3-5-8-13-21) en la ficha, las tarjetas, las columnas y el backlog; velocidad por sprint y aviso si un sprint planificado supera la media  |
@@ -28,7 +28,7 @@
 | 🌐 Web del colectivo | La página de cada proyecto en pireon.dev enseña su hoja de ruta, versiones, sprint y tickets para recién llegados (`good-first-issue`)                                    |
 | 🧩 Desglose          | Épicas → tickets → subtareas (tres niveles), con su progreso; y una checklist dentro de cada ticket para los pasos pequeños                                               |
 | 👀 Seguir            | Cualquier miembro sigue los tickets que le interesan; quien comenta, los sigue solo                                                                                       |
-| 🔔 Avisos            | Campana con lo que te concierne (asignaciones, cambios de estado, QA fallido, comentarios), en vivo y opcionalmente por correo                                            |
+| 🔔 Avisos            | Campana con lo que te concierne (asignaciones, cambios de estado, QA fallido, comentarios, respuestas), en vivo y opcionalmente por correo                                |
 | ⏰ Recordatorios     | Aviso (y correo, si se quiere) el día antes, el mismo día y al vencer la fecha límite, a quien lo tiene y a quien lo sigue; las tarjetas marcan lo que vence              |
 | 📎 Adjuntos          | Capturas, logs y vídeos en el ticket o bajo un comentario; arrastrar, elegir o pegar con Ctrl+V; miniaturas de las imágenes                                               |
 | 🔗 Relaciones        | `BLOCKS`, `DEPENDS_ON`, `TESTS`, `DUPLICATES`, `RELATES_TO`, también entre proyectos (FE ↔ BE ↔ QA)                                                                     |

docs/03-api.md

@@ -145,7 +145,11 @@ stateDiagram-v2
   Las notas de versión (`notes`, Markdown) se escriben también después de publicar (no una vez archivada);
   `notesDraft` / `GET /api/releases/{id}/notes/draft` propone un borrador con los tickets hechos agrupados por tipo
   (los de QA quedan fuera).
-- **Comentarios**: solo el autor edita; borra el autor o un admin del proyecto.
+- **Comentarios**: solo el autor edita; borra el autor o un admin del proyecto. Se puede responder a un comentario
+  (`replyTo`), con un solo nivel de respuestas: responder a una respuesta la suma al mismo hilo, y la respuesta tiene
+  que ser del mismo ticket. Quien escribió el comentario recibe un aviso (`REPLIED`). Un comentario borrado que tiene
+  respuestas se queda, sin texto (`deleted: true`), para que el hilo se siga entendiendo, y desaparece con su última
+  respuesta; no cuenta en `commentCount`.
 - **Cambios de UI**: `figmaUrl` debe ser un enlace `https://…figma.com/…`.
 - **Adjuntos**: los suben los miembros (no los lectores), hasta `ATTACHMENTS_MAX_MB` (25 MB) por archivo y 50 por
   ticket; pueden ir en el ticket o bajo uno de sus comentarios (`commentId`). Quita uno quien lo subió o un admin.
@@ -333,15 +337,15 @@ Todas devuelven `CommandResult { id, key, version }`.
 
 ### Subscriptions
 
-| Subscription                | Se emite cuando                                                                                            |
+| Subscription                | Se emite cuando                                                                                                     |
-| --------------------------- | ---------------------------------------------------------------------------------------------------------- |
+| --------------------------- | ------------------------------------------------------------------------------------------------------------------- |
-| `issueChanged(projectId)`   | Se crea o cambia cualquier ticket del proyecto (incluye el ticket completo y `action` = nombre del evento) |
+| `issueChanged(projectId)`   | Se crea o cambia cualquier ticket del proyecto (incluye el ticket completo y `action` = nombre del evento)          |
-| `commentChanged(issueId)`   | Se añade, edita o borra un comentario (`comment` es `null` al borrar)                                      |
+| `commentChanged(issueId)`   | Se añade, edita o borra un comentario (`comment` es `null` al borrar, o el que queda sin texto si tenía respuestas) |
-| `activityAdded(projectId)`  | Hay una nueva entrada en el feed                                                                           |
+| `activityAdded(projectId)`  | Hay una nueva entrada en el feed                                                                                    |
-| `releaseChanged(projectId)` | Cambia una release                                                                                         |
+| `releaseChanged(projectId)` | Cambia una release                                                                                                  |
-| `sprintChanged(projectId)`  | Se planifica, cambia, empieza, cierra o borra un sprint (`sprint` es `null` al borrar)                     |
+| `sprintChanged(projectId)`  | Se planifica, cambia, empieza, cierra o borra un sprint (`sprint` es `null` al borrar)                              |
-| `projectChanged(projectId)` | Cambian los datos, la configuración o los miembros del proyecto                                            |
+| `projectChanged(projectId)` | Cambian los datos, la configuración o los miembros del proyecto                                                     |
-| `myProjectsChanged`         | Me añaden a un proyecto o me quitan de uno                                                                 |
+| `myProjectsChanged`         | Me añaden a un proyecto o me quitan de uno                                                                          |
 
 Solo los miembros pueden suscribirse a un proyecto; las conexiones sin token válido se cierran con el código 4403.
 

docs/09-mcp.md

@@ -57,7 +57,7 @@ flowchart LR
 |              | `change_issue_status`                                                    | Mover de estado (con motivo cuando el estado lo pide)                                             |
 |              | `assign_issue`                                                           | Asignar o desasignar                                                                              |
 |              | `set_issue_release`                                                      | Meter en una release o sacar                                                                      |
-|              | `add_comment` / `edit_comment` / `delete_comment`                        | Comentar, corregir o borrar un comentario                                                         |
+|              | `add_comment` / `edit_comment` / `delete_comment`                        | Comentar (o responder a un comentario), corregir o borrar                                         |
 |              | `link_issues` / `unlink_issues`                                          | Relacionar tickets (`DEPENDS_ON`, `BLOCKS`, `TESTS`…) o quitar la relación                        |
 |              | `watch_issue`                                                            | Seguir un ticket o dejar de seguirlo                                                              |
 |              | `add_checklist_item` / `update_checklist_item` / `remove_checklist_item` | La lista de comprobación: añadir, marcar o reescribir, quitar                                     |

libs/api/tracker/application/src/lib/commands/add-comment.command-handler.ts

@@ -1,4 +1,5 @@
 import { CommandHandler, EventPublisher, ICommandHandler } from '@nestjs/cqrs';
+import { BusinessRuleError } from '@task-stream/api/shared/domain';
 import { CommentFactory } from '@task-stream/api/tracker/domain';
 import { AddCommentCommand } from './add-comment.command';
 import { CommandResult, ack } from './command-result';
@@ -24,10 +25,24 @@ export class AddCommentCommandHandler
       projectId: issue.projectId,
       authorId: command.actorId,
       body: command.body,
+      replyTo: command.replyTo
+        ? await this.threadOf(command.replyTo, issue.id)
+        : null,
     });
 
     this.eventPublisher.mergeObjectContext(comment);
     await comment.commitAndWait();
     return ack(comment);
   }
+
+  /**
+   * The top-level comment a reply hangs from: one level only, so answering
+   * a reply joins its thread.
+   */
+  private async threadOf(commentId: string, issueId: string): Promise<string> {
+    const parent = await this.access.comment(commentId);
+    if (parent.issueId !== issueId)
+      throw new BusinessRuleError('A reply must be on the same ticket');
+    return parent.replyTo ?? parent.id;
+  }
 }

libs/api/tracker/application/src/lib/commands/add-comment.command.ts

@@ -6,6 +6,8 @@ export class AddCommentCommand extends Command<CommandResult> {
     public readonly actorId: string,
     public readonly issueId: string,
     public readonly body: string,
+    /** Comment it answers; a reply to a reply joins the same thread. */
+    public readonly replyTo: string | null = null,
   ) {
     super();
   }

libs/api/tracker/application/src/lib/commands/commands.spec.ts

@@ -832,6 +832,38 @@ describe('tracker commands (event sourced)', () => {
     expect(rebuilt.deleted).toBe(true);
   });
 
+  it('answers comments one level deep, on the same ticket', async () => {
+    const { run, rehydrator } = await setup();
+    const projectId = await projectWithTeam(run);
+    const spike = await run(
+      new CreateIssueCommand('dev', projectId, IssueType.TASK, 'Spike', {}),
+    );
+    const other = await run(
+      new CreateIssueCommand('dev', projectId, IssueType.TASK, 'Other', {}),
+    );
+    const root = await run(new AddCommentCommand('dev', spike.id, 'Redis?'));
+    const reply = await run(
+      new AddCommentCommand('qa', spike.id, 'Sí', root.id),
+    );
+    // Answering a reply joins the same thread.
+    const again = await run(
+      new AddCommentCommand('dev', spike.id, 'Vale', reply.id),
+    );
+    const replyTo = async (id: string) =>
+      (await rehydrator.rehydrate(id, Comment)).replyTo;
+    expect(await replyTo(root.id)).toBeNull();
+    expect(await replyTo(reply.id)).toBe(root.id);
+    expect(await replyTo(again.id)).toBe(root.id);
+
+    await expect(
+      run(new AddCommentCommand('dev', other.id, 'Aquí no', root.id)),
+    ).rejects.toThrow(BusinessRuleError);
+    await run(new DeleteCommentCommand('qa', reply.id));
+    await expect(
+      run(new AddCommentCommand('dev', spike.id, 'Tarde', reply.id)),
+    ).rejects.toThrow(NotFoundError);
+  });
+
   it('detects concurrent modifications through stream positions', async () => {
     const { run, rehydrator } = await setup();
     const projectId = await projectWithTeam(run);

libs/api/tracker/application/src/lib/comments.service.ts

@@ -15,9 +15,14 @@ export class CommentsService {
     private readonly queryBus: QueryBus,
   ) {}
 
-  add(actorId: string, issueId: string, body: string): Promise<CommandResult> {
+  add(
+    actorId: string,
+    issueId: string,
+    body: string,
+    replyTo: string | null = null,
+  ): Promise<CommandResult> {
     return this.commandBus.execute(
-      new AddCommentCommand(actorId, issueId, body),
+      new AddCommentCommand(actorId, issueId, body, replyTo),
     );
   }
 

libs/api/tracker/application/src/lib/event-handlers/activity-summary.ts

@@ -200,7 +200,9 @@ export function describeEvent(
     return `${actor} quitó «${event.text}» de la lista de ${issueKey}`;
 
   if (event instanceof CommentAddedEvent)
-    return `${actor} comentó en ${issueKey}`;
+    return event.comment.replyTo
+      ? `${actor} respondió a un comentario en ${issueKey}`
+      : `${actor} comentó en ${issueKey}`;
   if (event instanceof CommentEditedEvent)
     return `${actor} editó un comentario en ${issueKey}`;
   if (event instanceof CommentDeletedEvent)

libs/api/tracker/application/src/lib/event-handlers/comment-added.event-handler.ts

@@ -27,6 +27,8 @@ export class CommentAddedEventHandler
       projectId: comment.projectId,
       author: users.of(comment.authorId),
       body: comment.body,
+      replyTo: comment.replyTo ?? null,
+      deleted: false,
       createdAt: comment.createdAt,
       editedAt: null,
       version: versionOf(event),

libs/api/tracker/application/src/lib/event-handlers/comment-deleted.event-handler.ts

@@ -3,7 +3,7 @@ import { CommentDeletedEvent } from '@task-stream/api/tracker/domain';
 import { FindCommentsRepository } from '../ports/find-comments.repository';
 import { UpsertMaterializedCommentRepository } from '../ports/upsert-materialized-comment.repository';
 import { UpsertMaterializedIssueRepository } from '../ports/upsert-materialized-issue.repository';
-import { ReadModelNotifier } from './read-model-notifier';
+import { ReadModelNotifier, versionOf } from './read-model-notifier';
 
 @EventsHandler(CommentDeletedEvent)
 export class CommentDeletedEventHandler
@@ -17,12 +17,35 @@ export class CommentDeletedEventHandler
   ) {}
 
   async handle(event: CommentDeletedEvent) {
-    await this.upsertMaterializedCommentRepository.remove(event.aggregateId);
+    const comment = await this.findComments.findById(event.aggregateId);
+    await this.vanishOrKeep(event.aggregateId, event);
+    // The last reply under a deleted comment takes it along.
+    const parent = comment?.replyTo
+      ? await this.findComments.findById(comment.replyTo)
+      : null;
+    if (parent?.deleted) await this.vanishOrKeep(parent.id, event);
     await this.upsertMaterializedIssueRepository.setCommentCount(
       event.issueId,
       await this.findComments.countByIssue(event.issueId),
     );
-    await this.notifier.comment(event.aggregateId, event.issueId, event);
     await this.notifier.issue(event.issueId, event);
   }
+
+  /**
+   * A comment with replies stays, without its text, so the conversation
+   * under it still reads; one without them goes.
+   */
+  private async vanishOrKeep(id: string, event: CommentDeletedEvent) {
+    if (await this.findComments.countReplies(id)) {
+      await this.upsertMaterializedCommentRepository.upsert({
+        id,
+        version: versionOf(event),
+        body: '',
+        deleted: true,
+      });
+    } else {
+      await this.upsertMaterializedCommentRepository.remove(id);
+    }
+    await this.notifier.comment(id, event.issueId, event);
+  }
 }

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

@@ -11,6 +11,7 @@ import {
   TrackerEvent,
   withoutMentionMarkup,
 } from '@task-stream/api/tracker/domain';
+import { FindCommentsRepository } from '../ports/find-comments.repository';
 import { FindIssuesRepository } from '../ports/find-issues.repository';
 import { FindProjectsRepository } from '../ports/find-projects.repository';
 import { UserDirectory } from '../ports/user-directory';
@@ -43,6 +44,7 @@ export class NotificationsEventHandler implements IEventHandler<TrackerEvent> {
     private readonly findIssues: FindIssuesRepository,
     private readonly findProjects: FindProjectsRepository,
     private readonly users: UserDirectory,
+    private readonly findComments: FindCommentsRepository,
   ) {}
 
   async handle(event: TrackerEvent): Promise<void> {
@@ -154,6 +156,16 @@ export class NotificationsEventHandler implements IEventHandler<TrackerEvent> {
           summary: `${actor} te mencionó en ${issue.key}: ${said}`,
         });
       }
+      const answered = event.comment.replyTo
+        ? await this.findComments.findById(event.comment.replyTo)
+        : null;
+      if (answered && !answered.deleted) {
+        drafts.push({
+          userId: answered.author.id,
+          kind: NotificationKind.REPLIED,
+          summary: `${actor} respondió a tu comentario en ${issue.key}: ${said}`,
+        });
+      }
       for (const userId of [assigneeId, reporterId]) {
         if (!userId) continue;
         drafts.push({

libs/api/tracker/application/src/lib/notifications/notifications.spec.ts

@@ -12,6 +12,7 @@ import {
 } from '@task-stream/api/tracker/domain';
 import { FakeUserDirectory } from '../../testing/in-memory';
 import { ChangeFeed } from '../ports/change-feed';
+import { FindCommentsRepository } from '../ports/find-comments.repository';
 import { FindIssuesRepository } from '../ports/find-issues.repository';
 import { FindProjectsRepository } from '../ports/find-projects.repository';
 import { NotificationMailer } from '../ports/notification-mailer';
@@ -100,6 +101,13 @@ function setup(mailEnabled = false) {
       }),
     } as unknown as FindProjectsRepository,
     users,
+    {
+      // A comment of the PM's, that others answer.
+      findById: async (id: string) =>
+        id === 'c-pm'
+          ? { id, author: { id: 'pm', name: 'PM' }, deleted: false }
+          : null,
+    } as unknown as FindCommentsRepository,
   );
   return { repo, published, mailed, handler };
 }
@@ -163,6 +171,7 @@ describe('notifications', () => {
         projectId: 'p-1',
         authorId: 'bob',
         body: 'Ya está arreglado',
+        replyTo: null,
         deleted: false,
         createdAt: '2026-10-08T10:00:00.000Z',
         editedAt: null,
@@ -185,6 +194,7 @@ describe('notifications', () => {
           projectId: 'p-1',
           authorId: 'bob',
           body: '@[PM](pm) mira esto, y @[Fuera](stranger) también',
+          replyTo: null,
           deleted: false,
           createdAt: '2026-10-08T10:00:00.000Z',
           editedAt: null,
@@ -200,6 +210,32 @@ describe('notifications', () => {
     expect(repo.all[0].summary).toContain('«@PM mira esto');
   });
 
+  it('tells whoever wrote a comment that someone answered it', async () => {
+    const { handler, repo } = setup();
+    await handler.handle(
+      at(
+        new CommentAddedEvent('bob', {
+          id: 'c-3',
+          issueId: 'i-1',
+          projectId: 'p-1',
+          authorId: 'bob',
+          body: 'Lo miro',
+          replyTo: 'c-pm',
+          deleted: false,
+          createdAt: '2026-10-08T10:00:00.000Z',
+          editedAt: null,
+        }),
+        1,
+      ),
+    );
+
+    expect(repo.all.map((n) => [n.userId, n.kind])).toEqual([
+      ['pm', NotificationKind.REPLIED],
+      ['qa', NotificationKind.COMMENTED],
+    ]);
+    expect(repo.all[0].summary).toContain('respondió a tu comentario');
+  });
+
   it('copies by e-mail only to whoever asked for it, when mail is configured', async () => {
     const { handler, repo, mailed } = setup(true);
     repo.emailOn.add('bob');

libs/api/tracker/application/src/lib/ports/find-comments.repository.ts

@@ -8,5 +8,7 @@ export abstract class FindCommentsRepository {
     limit: number,
     offset: number,
   ): Promise<Page<CommentReadModel>>;
+  /** Comments still standing (deleted ones kept for their replies do not count). */
   abstract countByIssue(issueId: string): Promise<number>;
+  abstract countReplies(commentId: string): Promise<number>;
 }

libs/api/tracker/application/src/lib/sagas/commenters-follow.saga.spec.ts

@@ -11,6 +11,7 @@ describe('CommentersFollowSaga', () => {
       projectId: 'p-1',
       authorId: 'ana',
       body: 'Lo miro',
+      replyTo: null,
       deleted: false,
       createdAt: '2026-10-08T10:00:00.000Z',
       editedAt: null,

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. */

libs/api/tracker/infrastructure/src/lib/mongo/find.repositories.ts

@@ -45,6 +45,13 @@ import {
 
 /* Query-side adapters (MongoDB). */
 
+/** Comments projected before there were replies have neither field. */
+const commentFromDoc = (doc: CommentDoc): CommentReadModel => ({
+  ...fromDoc(doc),
+  replyTo: doc.replyTo ?? null,
+  deleted: doc.deleted ?? false,
+});
+
 const escapeRegex = (text: string) =>
   text.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
 
@@ -446,7 +453,7 @@ export class MongoFindCommentsRepository extends FindCommentsRepository {
 
   async findById(id: string): Promise<CommentReadModel | null> {
     const doc = await this.comments.findById(id).lean<CommentDoc>();
-    return doc ? fromDoc(doc) : null;
+    return doc ? commentFromDoc(doc) : null;
   }
 
   async findByIssue(
@@ -463,11 +470,15 @@ export class MongoFindCommentsRepository extends FindCommentsRepository {
         .lean<CommentDoc[]>(),
       this.comments.countDocuments({ issueId }),
     ]);
-    return { items: docs.map(fromDoc), total };
+    return { items: docs.map(commentFromDoc), total };
   }
 
   countByIssue(issueId: string): Promise<number> {
-    return this.comments.countDocuments({ issueId });
+    return this.comments.countDocuments({ issueId, deleted: { $ne: true } });
+  }
+
+  countReplies(commentId: string): Promise<number> {
+    return this.comments.countDocuments({ replyTo: commentId });
   }
 }
 

libs/api/tracker/infrastructure/src/lib/mongo/read-model.schemas.ts

@@ -151,6 +151,7 @@ export const CommentSchema = new Schema<CommentDoc>(
   {
     _id: String,
     issueId: { type: String, index: true },
+    replyTo: { type: String, index: true },
     author: userRef,
     version: Number,
   },

libs/api/tracker/presenters/src/lib/graphql/comment.resolver.ts

@@ -8,13 +8,18 @@ import { CommandResultGql, CommentGql } from './types';
 export class CommentResolver {
   constructor(private readonly comments: CommentsService) {}
 
-  @Mutation(() => CommandResultGql)
+  @Mutation(() => CommandResultGql, {
+    description:
+      'Comment on a ticket, or answer a comment (replyTo; one level of replies)',
+  })
   addComment(
     @CurrentUser() me: User,
     @Args('issueId', { type: () => ID }) issueId: string,
     @Args('body') body: string,
+    @Args('replyTo', { type: () => ID, nullable: true })
+    replyTo: string | null,
   ) {
-    return this.comments.add(me.id, issueId, body);
+    return this.comments.add(me.id, issueId, body, replyTo ?? null);
   }
 
   @Mutation(() => CommandResultGql)

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

@@ -445,7 +445,17 @@ export class CommentGql {
   @Field(() => ID) id!: string;
   @Field(() => ID) issueId!: string;
   @Field(() => UserRefGql) author!: UserRefGql;
-  @Field() body!: string;
+  @Field({ description: 'Empty on a deleted comment kept for its replies' })
+  body!: string;
+  @Field(() => ID, {
+    nullable: true,
+    description: 'The top-level comment it answers; null for a top-level one',
+  })
+  replyTo!: string | null;
+  @Field({
+    description: 'Deleted, but kept (without its text) while it has replies',
+  })
+  deleted!: boolean;
   @Field() createdAt!: string;
   @Field(() => String, { nullable: true }) editedAt!: string | null;
   @Field(() => Int) version!: number;

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

@@ -955,6 +955,17 @@ export class CommentBodyDto {
   body!: string;
 }
 
+export class AddCommentDto extends CommentBodyDto {
+  @ApiPropertyOptional({
+    format: 'uuid',
+    description:
+      'Comment it answers (one level: answering a reply joins its thread)',
+  })
+  @IsOptional()
+  @IsUUID()
+  replyTo?: string;
+}
+
 // ---- Releases ---------------------------------------------------------------
 
 export class CreateReleaseDto {

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

@@ -466,7 +466,21 @@ export class CommentDto {
   @ApiProperty({ format: 'uuid' }) id!: string;
   @ApiProperty({ format: 'uuid' }) issueId!: string;
   @ApiProperty({ type: UserRefDto }) author!: UserRefDto;
-  @ApiProperty() body!: string;
+  @ApiProperty({
+    description: 'Empty on a deleted comment kept for its replies',
+  })
+  body!: string;
+  @ApiProperty({
+    type: String,
+    nullable: true,
+    format: 'uuid',
+    description: 'The top-level comment it answers; null for a top-level one',
+  })
+  replyTo!: string | null;
+  @ApiProperty({
+    description: 'Deleted, but kept (without its text) while it has replies',
+  })
+  deleted!: boolean;
   @ApiProperty({ format: 'date-time' }) createdAt!: string;
   @ApiProperty({ type: String, nullable: true, format: 'date-time' })
   editedAt!: string | null;

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

@@ -39,7 +39,7 @@ import {
   BulkUpdateIssuesDto,
   ChangeStatusDto,
   ChecklistItemBodyDto,
-  CommentBodyDto,
+  AddCommentDto,
   CreateIssueDto,
   IssueSearchQueryDto,
   LinkIssueDto,
@@ -529,18 +529,21 @@ export class IssuesController {
 
   @Post('issues/:issue/comments')
   @ISSUE
-  @ApiOperation({ summary: 'Comment on the ticket' })
+  @ApiOperation({
+    summary: 'Comment on the ticket, or answer a comment (replyTo)',
+  })
   @ApiCreatedResponse({ type: CommandResultDto })
   @ApiCommandErrors()
   async addComment(
     @CurrentUser() me: User,
     @Param('issue') issue: string,
-    @Body() body: CommentBodyDto,
+    @Body() body: AddCommentDto,
   ) {
     return this.comments.add(
       me.id,
       await this.refs.issueId(me.id, issue),
       body.body,
+      body.replyTo ?? null,
     );
   }
 

libs/web/tracker/application/src/lib/events/issue.events.ts

@@ -39,6 +39,8 @@ export const issuePageEvents = eventGroup({
       body: string;
       /** Uploaded under the new comment once it exists. */
       files?: File[];
+      /** Comment it answers (one level of replies). */
+      replyTo?: string | null;
     }>(),
     watchRequested: type<{ issueId: string; watching: boolean }>(),
     trashRequested: type<{ issueId: string; trashed: boolean }>(),

libs/web/tracker/application/src/lib/facades/issue.facade.ts

@@ -92,10 +92,14 @@ export class IssueFacade {
     );
   }
 
-  /** `files` are attached under the new comment. */
+  /** `files` are attached under the new comment; `replyTo` answers one. */
-  addComment(body: string, files: File[] = []): void {
+  addComment(
+    body: string,
+    files: File[] = [],
+    replyTo: string | null = null,
+  ): void {
     this.withIssue((issueId) =>
-      this.dispatch.commentAddRequested({ issueId, body, files }),
+      this.dispatch.commentAddRequested({ issueId, body, files, replyTo }),
     );
   }
 

libs/web/tracker/application/src/lib/stores/issue.store.ts

@@ -460,7 +460,7 @@ export const IssueStore = signalStore(
               mergeMap(({ payload }) =>
                 runCommand(
                   comments
-                    .add(payload.issueId, payload.body)
+                    .add(payload.issueId, payload.body, payload.replyTo ?? null)
                     .pipe(
                       concatMap((comment) =>
                         payload.files?.length
@@ -474,7 +474,9 @@ export const IssueStore = signalStore(
                     ),
                   payload.files?.length
                     ? 'Comentario y adjuntos añadidos'
-                    : 'Comentario añadido',
+                    : payload.replyTo
+                      ? 'Respuesta añadida'
+                      : 'Comentario añadido',
                   done,
                   failed,
                 ),

libs/web/tracker/domain/src/lib/models/enums.ts

@@ -53,6 +53,7 @@ export enum NotificationKind {
   QA_FAILED = 'QA_FAILED',
   COMMENTED = 'COMMENTED',
   MENTIONED = 'MENTIONED',
+  REPLIED = 'REPLIED',
   WATCHED = 'WATCHED',
   ADDED_TO_PROJECT = 'ADDED_TO_PROJECT',
   REMINDER = 'REMINDER',

libs/web/tracker/domain/src/lib/models/models.ts

@@ -269,7 +269,12 @@ export interface Comment {
   id: string;
   issueId: string;
   author: UserRef;
+  /** Empty on a deleted comment kept for its replies. */
   body: string;
+  /** The top-level comment it answers; null for a top-level one. */
+  replyTo: string | null;
+  /** Deleted, but kept (without its text) while it has replies. */
+  deleted: boolean;
   createdAt: string;
   editedAt: string | null;
 }

libs/web/tracker/domain/src/lib/ports/gateways.ts

@@ -230,7 +230,11 @@ export abstract class SavedFiltersGateway {
 
 export abstract class CommentsGateway {
   abstract list(issueId: string): Observable<Comment[]>;
-  abstract add(issueId: string, body: string): Observable<CommandResult>;
+  abstract add(
+    issueId: string,
+    body: string,
+    replyTo?: string | null,
+  ): Observable<CommandResult>;
   abstract edit(commentId: string, body: string): Observable<CommandResult>;
   abstract remove(commentId: string): Observable<CommandResult>;
 }

libs/web/tracker/infrastructure/src/lib/adapters/graphql-collaboration.gateways.ts

@@ -42,9 +42,13 @@ export class GraphqlCommentsGateway extends CommentsGateway {
       .pipe(map((d) => d.issue.comments.items.map(toComment)));
   }
 
-  add(issueId: string, body: string): Observable<CommandResult> {
+  add(
+    issueId: string,
+    body: string,
+    replyTo: string | null = null,
+  ): Observable<CommandResult> {
     return this.gql
-      .mutate(AddCommentDocument, { issueId, body })
+      .mutate(AddCommentDocument, { issueId, body, replyTo })
       .pipe(map((d) => toCommandResult(d.addComment)));
   }
 

libs/web/tracker/infrastructure/src/lib/graphql/fragments.graphql

@@ -141,6 +141,8 @@ fragment CommentFields on Comment {
   id
   issueId
   body
+  replyTo
+  deleted
   createdAt
   editedAt
   author {

libs/web/tracker/infrastructure/src/lib/graphql/generated.ts

@@ -212,6 +212,7 @@ export type NotificationKind =
   | 'MENTIONED'
   | 'QA_FAILED'
   | 'REMINDER'
+  | 'REPLIED'
   | 'STATUS_CHANGED'
   | 'WATCHED';
 
@@ -554,6 +555,8 @@ export type CommentFieldsFragment = {
   id: string;
   issueId: string;
   body: string;
+  replyTo: string | null;
+  deleted: boolean;
   createdAt: string;
   editedAt: string | null;
   author: { id: string; name: string };
@@ -875,6 +878,8 @@ export type IssueCommentsQuery = {
         id: string;
         issueId: string;
         body: string;
+        replyTo: string | null;
+        deleted: boolean;
         createdAt: string;
         editedAt: string | null;
         author: { id: string; name: string };
@@ -886,6 +891,7 @@ export type IssueCommentsQuery = {
 export type AddCommentMutationVariables = Exact<{
   issueId: string;
   body: string;
+  replyTo?: string | null | undefined;
 }>;
 
 export type AddCommentMutation = {
@@ -1853,6 +1859,8 @@ export type CommentChangedSubscription = {
       id: string;
       issueId: string;
       body: string;
+      replyTo: string | null;
+      deleted: boolean;
       createdAt: string;
       editedAt: string | null;
       author: { id: string; name: string };
@@ -2698,6 +2706,8 @@ export const CommentFieldsFragmentDoc = {
           { kind: 'Field', name: { kind: 'Name', value: 'id' } },
           { kind: 'Field', name: { kind: 'Name', value: 'issueId' } },
           { kind: 'Field', name: { kind: 'Name', value: 'body' } },
+          { kind: 'Field', name: { kind: 'Name', value: 'replyTo' } },
+          { kind: 'Field', name: { kind: 'Name', value: 'deleted' } },
           { kind: 'Field', name: { kind: 'Name', value: 'createdAt' } },
           { kind: 'Field', name: { kind: 'Name', value: 'editedAt' } },
           {
@@ -5477,6 +5487,8 @@ export const IssueCommentsDocument = {
           { kind: 'Field', name: { kind: 'Name', value: 'id' } },
           { kind: 'Field', name: { kind: 'Name', value: 'issueId' } },
           { kind: 'Field', name: { kind: 'Name', value: 'body' } },
+          { kind: 'Field', name: { kind: 'Name', value: 'replyTo' } },
+          { kind: 'Field', name: { kind: 'Name', value: 'deleted' } },
           { kind: 'Field', name: { kind: 'Name', value: 'createdAt' } },
           { kind: 'Field', name: { kind: 'Name', value: 'editedAt' } },
           {
@@ -5527,6 +5539,14 @@ export const AddCommentDocument = {
             },
           },
         },
+        {
+          kind: 'VariableDefinition',
+          variable: {
+            kind: 'Variable',
+            name: { kind: 'Name', value: 'replyTo' },
+          },
+          type: { kind: 'NamedType', name: { kind: 'Name', value: 'ID' } },
+        },
       ],
       selectionSet: {
         kind: 'SelectionSet',
@@ -5551,6 +5571,14 @@ export const AddCommentDocument = {
                   name: { kind: 'Name', value: 'body' },
                 },
               },
+              {
+                kind: 'Argument',
+                name: { kind: 'Name', value: 'replyTo' },
+                value: {
+                  kind: 'Variable',
+                  name: { kind: 'Name', value: 'replyTo' },
+                },
+              },
             ],
             selectionSet: {
               kind: 'SelectionSet',
@@ -11232,6 +11260,8 @@ export const CommentChangedDocument = {
           { kind: 'Field', name: { kind: 'Name', value: 'id' } },
           { kind: 'Field', name: { kind: 'Name', value: 'issueId' } },
           { kind: 'Field', name: { kind: 'Name', value: 'body' } },
+          { kind: 'Field', name: { kind: 'Name', value: 'replyTo' } },
+          { kind: 'Field', name: { kind: 'Name', value: 'deleted' } },
           { kind: 'Field', name: { kind: 'Name', value: 'createdAt' } },
           { kind: 'Field', name: { kind: 'Name', value: 'editedAt' } },
           {

libs/web/tracker/infrastructure/src/lib/graphql/issues.graphql

@@ -112,8 +112,8 @@ query IssueComments($idOrKey: String!) {
   }
 }
 
-mutation AddComment($issueId: ID!, $body: String!) {
+mutation AddComment($issueId: ID!, $body: String!, $replyTo: ID) {
-  addComment(issueId: $issueId, body: $body) {
+  addComment(issueId: $issueId, body: $body, replyTo: $replyTo) {
     ...CommandResultFields
   }
 }

libs/web/tracker/presenters/src/lib/pages/issue.page.scss

@@ -531,3 +531,32 @@ a.ts-key {
   border-radius: 0.5rem;
   background: color-mix(in srgb, var(--ts-c-red, #dc2626) 12%, transparent);
 }
+
+// One level of replies under each comment.
+.ts-replies {
+  display: grid;
+  gap: 0.75rem;
+  margin: -0.25rem 0 0.5rem 2.75rem;
+  padding-left: 0.875rem;
+  border-left: 2px solid var(--ts-line);
+
+  &:empty {
+    display: none;
+  }
+}
+
+.ts-comment__gone {
+  margin: 0;
+  font-style: italic;
+}
+
+.ts-reply__open {
+  justify-self: start;
+  font-size: 0.8125rem;
+}
+
+.ts-reply__actions {
+  display: flex;
+  gap: 0.75rem;
+  align-items: center;
+}

libs/web/tracker/presenters/src/lib/pages/issue.page.ts

@@ -1,3 +1,4 @@
+import { NgTemplateOutlet } from '@angular/common';
 import {
   ChangeDetectionStrategy,
   Component,
@@ -71,6 +72,7 @@ const MAX_FILE_BYTES = 25 * 1024 * 1024;
   selector: 'ts-issue-page',
   changeDetection: ChangeDetectionStrategy.OnPush,
   imports: [
+    NgTemplateOutlet,
     RouterLink,
     FormField,
     AttachmentItem,
@@ -512,22 +514,24 @@ const MAX_FILE_BYTES = 25 * 1024 * 1024;
           <article class="ts-block">
             <h2 class="ts-section">
               Comentarios
-              <span class="ts-mono">{{ facade.comments().length }}</span>
+              <span class="ts-mono">{{ commentCount() }}</span>
             </h2>
-            @for (comment of facade.comments(); track comment.id) {
+            <ng-template #commentView let-comment>
               <div class="ts-comment">
                 <span class="ts-comment__avatar" aria-hidden="true">{{
                   initialsOf(comment.author.name)
                 }}</span>
                 <div class="ts-comment__body">
                   <div class="ts-comment__head">
-                    <strong>{{ comment.author.name }}</strong>
+                    <strong>{{
+                      comment.deleted ? '—' : comment.author.name
+                    }}</strong>
                     <span class="ts-comment__when"
                       >{{ ago(comment.createdAt)
                       }}{{ comment.editedAt ? ' · editado' : '' }}</span
                     >
                     <span class="ts-spacer"></span>
-                    @if (comment.author.id === facade.me()) {
+                    @if (!comment.deleted && comment.author.id === facade.me()) {
                       <pi-icon-button
                         icon="edit"
                         color="grey"
@@ -537,7 +541,8 @@ const MAX_FILE_BYTES = 25 * 1024 * 1024;
                       />
                     }
                     @if (
-                      comment.author.id === facade.me() || project.canManage()
+                      !comment.deleted &&
+                      (comment.author.id === facade.me() || project.canManage())
                     ) {
                       <pi-icon-button
                         icon="trash"
@@ -548,6 +553,9 @@ const MAX_FILE_BYTES = 25 * 1024 * 1024;
                       />
                     }
                   </div>
+                  @if (comment.deleted) {
+                    <p class="ts-muted ts-comment__gone">Comentario borrado</p>
+                  } @else {
                   <p class="ts-prewrap">
                     @for (part of segments(comment.body); track $index) {
                       @if ('mention' in part) {
@@ -561,7 +569,8 @@ const MAX_FILE_BYTES = 25 * 1024 * 1024;
                       }
                     }
                   </p>
-                  @if (filesOf(comment).length) {
+                  }
+                  @if (!comment.deleted && filesOf(comment).length) {
                     <div class="ts-attachments">
                       @for (file of filesOf(comment); track file.id) {
                         <ts-attachment
@@ -573,6 +582,57 @@ const MAX_FILE_BYTES = 25 * 1024 * 1024;
                   }
                 </div>
               </div>
+            </ng-template>
+            @for (thread of threads(); track thread.comment.id) {
+              <ng-container
+                *ngTemplateOutlet="commentView; context: { $implicit: thread.comment }"
+              />
+              <div class="ts-replies">
+                @for (reply of thread.replies; track reply.id) {
+                  <ng-container
+                    *ngTemplateOutlet="commentView; context: { $implicit: reply }"
+                  />
+                }
+                @if (replyingTo() === thread.comment.id) {
+                  <form
+                    class="ts-form ts-reply"
+                    (submit)="$event.preventDefault(); reply(thread.comment)"
+                    novalidate
+                  >
+                    <pi-textarea
+                      [placeholder]="'Responde a ' + thread.comment.author.name + '…'"
+                      [(value)]="replyBody"
+                    />
+                    <div class="ts-reply__actions">
+                      <pi-action-button
+                        color="primary"
+                        text="Responder"
+                        [disabled]="!replyBody().trim()"
+                        (execute)="reply(thread.comment)"
+                      />
+                      <button
+                        type="button"
+                        class="ts-plain-link"
+                        (click)="replyingTo.set(null)"
+                      >
+                        Cancelar
+                      </button>
+                    </div>
+                  </form>
+                } @else if (project.canContribute() && !thread.comment.deleted) {
+                  <button
+                    type="button"
+                    class="ts-plain-link ts-reply__open"
+                    (click)="startReply(thread.comment)"
+                  >
+                    Responder{{
+                      thread.replies.length
+                        ? ' (' + thread.replies.length + ')'
+                        : ''
+                    }}
+                  </button>
+                }
+              </div>
             }
             @if (project.canContribute()) {
               <form
@@ -934,6 +994,25 @@ export class IssuePage {
   protected readonly linkType = signal<string | null>(IssueLinkType.RELATES_TO);
   protected readonly linkTarget = signal('');
   protected readonly commentBody = signal('');
+  /** The comment being answered, and the answer being written. */
+  protected readonly replyingTo = signal<string | null>(null);
+  protected readonly replyBody = signal('');
+  /** Top-level comments, each with its replies (oldest first). */
+  protected readonly threads = computed(() => {
+    const comments = this.facade.comments();
+    const ids = new Set(comments.map((c) => c.id));
+    const replies = new Map<string, Comment[]>();
+    for (const c of comments)
+      if (c.replyTo && ids.has(c.replyTo))
+        replies.set(c.replyTo, [...(replies.get(c.replyTo) ?? []), c]);
+    // A reply whose comment did not load stands on its own.
+    return comments
+      .filter((c) => !c.replyTo || !ids.has(c.replyTo))
+      .map((comment) => ({ comment, replies: replies.get(comment.id) ?? [] }));
+  });
+  protected readonly commentCount = computed(
+    () => this.facade.comments().filter((c) => !c.deleted).length,
+  );
   protected readonly commentFiles = signal<File[]>([]);
   protected readonly segments = mentionSegments;
   /** Members matching what is typed after an `@` at the end of the comment. */
@@ -1126,6 +1205,19 @@ export class IssuePage {
     this.commentFiles.set([]);
   }
 
+  protected startReply(comment: Comment): void {
+    this.replyBody.set('');
+    this.replyingTo.set(comment.id);
+  }
+
+  protected reply(comment: Comment): void {
+    const body = this.replyBody().trim();
+    if (!body) return;
+    this.facade.addComment(body, [], comment.id);
+    this.replyBody.set('');
+    this.replyingTo.set(null);
+  }
+
   protected mention(user: { id: string; name: string }): void {
     this.commentBody.update((text) => insertMention(text, user));
   }

libs/web/tracker/presenters/src/lib/ui/notifications-bell.ts

@@ -27,6 +27,7 @@ const ICON: Record<NotificationKind, string> = {
   [NotificationKind.QA_FAILED]: 'exclamation',
   [NotificationKind.COMMENTED]: 'chat',
   [NotificationKind.MENTIONED]: 'chat',
+  [NotificationKind.REPLIED]: 'chat',
   [NotificationKind.WATCHED]: 'focus',
   [NotificationKind.ADDED_TO_PROJECT]: 'briefcase',
   [NotificationKind.REMINDER]: 'calendar',