diff --git a/apps/api/src/app/app.module.ts b/apps/api/src/app/app.module.ts
index af7a998..88505fa 100644
--- a/apps/api/src/app/app.module.ts
+++ b/apps/api/src/app/app.module.ts
@@ -47,6 +47,8 @@ const tracker = TrackerPresentersModule.withApplication(
         url: config.getOrThrow<string>('POSTGRES_URL'),
         autoLoadEntities: true,
         synchronize: config.get<boolean>('POSTGRES_SYNCHRONIZE'),
+        // uuid ids come from gen_random_uuid() (core since PostgreSQL 13).
+        uuidExtension: 'pgcrypto',
       }),
     }),
 
diff --git a/docs/02-arquitectura.md b/docs/02-arquitectura.md
index c8900e2..5987c21 100644
--- a/docs/02-arquitectura.md
+++ b/docs/02-arquitectura.md
@@ -103,6 +103,9 @@ sequenceDiagram
   segunda falla con `ConcurrencyError` (código GraphQL `CONFLICT`).
 - **Lookups**: lo que no se puede comprobar dentro de un agregado vive en tablas aparte: claves de proyecto únicas
   (`project_keys`), numeración de tickets (`issue_sequences`) y nombres de release únicos (`release_names`).
+- **Ids**: todas las tablas tienen `id uuid` (`gen_random_uuid()`); lo que hace única una fila de lookup es una
+  restricción aparte (la clave, el proyecto, proyecto + nombre). En `events`, el orden global con el que se reenvían los
+  eventos va en `seq` (`bigserial`), porque un uuid no se ordena; `stream_id` es el id del agregado.
 
 ### De escritura a lectura: Redis
 
@@ -122,6 +125,10 @@ sequenceDiagram
   que reentregar un evento no tiene efecto.
 - Las queries leen por los puertos `Find*Repository`. Los read models (`ProjectReadModel`, `IssueReadModel`…) están en
   `domain/read-models`.
+- **Ids**: cada documento tiene `_id` (el `ObjectId` de Mongo, que no sale de la base de datos) e `id` con índice
+  único, que es el id del dominio: el mismo uuid que el `stream_id` del agregado en Postgres. Todas las consultas van
+  por `id`. En usuarios es el id de Pireon; en actividad, historial y avisos, uno compuesto que hace idempotente la
+  proyección.
 
 ### Tiempo real
 
diff --git a/docs/10-futuro.md b/docs/10-futuro.md
index b0fe257..3fe2d2e 100644
--- a/docs/10-futuro.md
+++ b/docs/10-futuro.md
@@ -65,3 +65,6 @@ Mucho trabajo para lo que aportan hoy; se pueden recuperar si alguien los necesi
 - Paquete inicial de la web de 2,13 MB a 1,88 MB con `@pi/ui` 0.0.4, que ya no registra Chart.js al importarse ni
   depende de `lodash`.
 - Descripciones y comentarios con editor visual (guardado en Markdown), con menciones y capturas pegadas.
+- Ids: `uuid` en todas las tablas de Postgres (el orden de los eventos en `seq`) y, en Mongo, `id` con el uuid del
+  dominio más el `_id` `ObjectId` propio.
+- Enlazar tickets y colgar de un padre eligiendo en un selector con búsqueda; casillas de `@pi/ui` en toda la web.
diff --git a/docs/TaskStream-Documentacion.docx b/docs/TaskStream-Documentacion.docx
index 9672563..f4772b7 100644
Binary files a/docs/TaskStream-Documentacion.docx and b/docs/TaskStream-Documentacion.docx differ
diff --git a/docs/TaskStream-Documentacion.pdf b/docs/TaskStream-Documentacion.pdf
index b12f809..699a479 100644
Binary files a/docs/TaskStream-Documentacion.pdf and b/docs/TaskStream-Documentacion.pdf differ
diff --git a/libs/api/identity/infrastructure/src/lib/mongo/mongo-user.registry.ts b/libs/api/identity/infrastructure/src/lib/mongo/mongo-user.registry.ts
index 5629cfe..92c567a 100644
--- a/libs/api/identity/infrastructure/src/lib/mongo/mongo-user.registry.ts
+++ b/libs/api/identity/infrastructure/src/lib/mongo/mongo-user.registry.ts
@@ -16,20 +16,20 @@ export class MongoUserRegistry extends UserRegistry {
 
   async upsert(user: User): Promise<void> {
     await this.users.updateOne(
-      { _id: user.id },
+      { id: user.id },
       { $set: { name: user.name, email: user.email, isActive: user.isActive } },
       { upsert: true },
     );
   }
 
   async findById(id: string): Promise<User | null> {
-    const doc = await this.users.findById(id).lean();
+    const doc = await this.users.findOne({ id }).lean();
     return doc ? this.toUser(doc) : null;
   }
 
   async findByIds(ids: string[]): Promise<User[]> {
     if (ids.length === 0) return [];
-    const docs = await this.users.find({ _id: { $in: ids } }).lean();
+    const docs = await this.users.find({ id: { $in: ids } }).lean();
     return docs.map((d) => this.toUser(d));
   }
 
@@ -48,7 +48,7 @@ export class MongoUserRegistry extends UserRegistry {
 
   private toUser(doc: UserDocument): User {
     return this.factory.restore({
-      id: doc._id,
+      id: doc.id,
       name: doc.name,
       email: doc.email,
       isActive: doc.isActive,
diff --git a/libs/api/identity/infrastructure/src/lib/mongo/user.schema.ts b/libs/api/identity/infrastructure/src/lib/mongo/user.schema.ts
index 5851ce9..ba5c652 100644
--- a/libs/api/identity/infrastructure/src/lib/mongo/user.schema.ts
+++ b/libs/api/identity/infrastructure/src/lib/mongo/user.schema.ts
@@ -2,8 +2,9 @@ import { Prop, Schema, SchemaFactory } from '@nestjs/mongoose';
 
 @Schema({ collection: 'users', timestamps: true, versionKey: false })
 export class UserDocument {
-  @Prop({ type: String, required: true })
-  _id!: string;
+  /** The user's id at Pireon; `_id` is Mongo's own ObjectId. */
+  @Prop({ type: String, required: true, unique: true })
+  id!: string;
 
   @Prop({ required: true })
   name!: string;
diff --git a/libs/api/shared/infrastructure/src/lib/event-store/entities/event.entity.ts b/libs/api/shared/infrastructure/src/lib/event-store/entities/event.entity.ts
index 289c290..b8dada8 100644
--- a/libs/api/shared/infrastructure/src/lib/event-store/entities/event.entity.ts
+++ b/libs/api/shared/infrastructure/src/lib/event-store/entities/event.entity.ts
@@ -2,6 +2,7 @@ import {
   Column,
   CreateDateColumn,
   Entity,
+  Generated,
   Index,
   PrimaryGeneratedColumn,
   Unique,
@@ -13,12 +14,21 @@ import {
  */
 @Entity('events')
 @Unique('uq_events_stream_position', ['streamId', 'position'])
-@Index('idx_events_unpublished', ['id'], { where: '"published_at" IS NULL' })
+@Index('idx_events_unpublished', ['seq'], { where: '"published_at" IS NULL' })
 export class EventEntity {
-  /** Global order of the store, used to relay events in sequence. */
-  @PrimaryGeneratedColumn('increment', { type: 'bigint' })
+  /** The event's own id. */
+  @PrimaryGeneratedColumn('uuid')
   id!: string;
 
+  /**
+   * Global order of the store, used to relay events in sequence. A uuid has
+   * no reliable order, so it is kept apart.
+   */
+  @Index('uq_events_seq', { unique: true })
+  @Column({ type: 'bigint' })
+  @Generated('increment')
+  seq!: string;
+
   @Column({ name: 'stream_id', length: 64 })
   streamId!: string;
 
diff --git a/libs/api/shared/infrastructure/src/lib/event-store/event-store.relay.ts b/libs/api/shared/infrastructure/src/lib/event-store/event-store.relay.ts
index fb43a61..6540c23 100644
--- a/libs/api/shared/infrastructure/src/lib/event-store/event-store.relay.ts
+++ b/libs/api/shared/infrastructure/src/lib/event-store/event-store.relay.ts
@@ -73,7 +73,7 @@ export class EventStoreRelay
         .getRepository(EventEntity)
         .createQueryBuilder('e')
         .where('e.published_at IS NULL')
-        .orderBy('e.id', 'ASC')
+        .orderBy('e.seq', 'ASC')
         .limit(BATCH_SIZE)
         .setLock('pessimistic_write')
         .setOnLocked('skip_locked')
diff --git a/libs/api/tracker/infrastructure/src/lib/mongo/automations.repository.ts b/libs/api/tracker/infrastructure/src/lib/mongo/automations.repository.ts
index 81745ef..56f1a9c 100644
--- a/libs/api/tracker/infrastructure/src/lib/mongo/automations.repository.ts
+++ b/libs/api/tracker/infrastructure/src/lib/mongo/automations.repository.ts
@@ -41,12 +41,14 @@ export class MongoAutomationsRepository extends AutomationsRepository {
   }
 
   async findById(id: string): Promise<Automation | null> {
-    const doc = await this.automations.findById(id).lean<AutomationDoc>();
+    const doc = await this.automations
+      .findOne({ id: id })
+      .lean<AutomationDoc>();
     return doc ? (fromDoc(doc) as Automation) : null;
   }
 
   async insert({ id, ...rest }: Automation): Promise<void> {
-    await this.automations.create({ _id: id, ...rest });
+    await this.automations.create({ id, ...rest });
   }
 
   async update(
@@ -54,16 +56,16 @@ export class MongoAutomationsRepository extends AutomationsRepository {
     changes: Partial<Pick<Automation, 'name' | 'active'>>,
   ): Promise<void> {
     if (Object.keys(changes).length)
-      await this.automations.updateOne({ _id: id }, { $set: changes });
+      await this.automations.updateOne({ id }, { $set: changes });
   }
 
   async delete(id: string): Promise<void> {
-    await this.automations.deleteOne({ _id: id });
+    await this.automations.deleteOne({ id });
   }
 
   async claimRun(ruleId: string, eventKey: string): Promise<boolean> {
     try {
-      await this.runs.create({ _id: `${ruleId}:${eventKey}`, at: new Date() });
+      await this.runs.create({ id: `${ruleId}:${eventKey}`, at: new Date() });
       return true;
     } catch (error) {
       if ((error as { code?: number }).code === DUPLICATE_KEY) return false;
@@ -73,7 +75,7 @@ export class MongoAutomationsRepository extends AutomationsRepository {
 
   async recordRun(id: string, error: string | null): Promise<void> {
     await this.automations.updateOne(
-      { _id: id },
+      { id },
       {
         $inc: { runs: 1 },
         $set: { lastRunAt: new Date().toISOString(), lastError: error },
diff --git a/libs/api/tracker/infrastructure/src/lib/mongo/find.repositories.ts b/libs/api/tracker/infrastructure/src/lib/mongo/find.repositories.ts
index 49fad10..2accac6 100644
--- a/libs/api/tracker/infrastructure/src/lib/mongo/find.repositories.ts
+++ b/libs/api/tracker/infrastructure/src/lib/mongo/find.repositories.ts
@@ -79,7 +79,7 @@ export class MongoFindProjectsRepository extends FindProjectsRepository {
   }
 
   async findById(id: string): Promise<ProjectReadModel | null> {
-    const doc = await this.projects.findById(id).lean<ProjectDoc>();
+    const doc = await this.projects.findOne({ id: id }).lean<ProjectDoc>();
     return doc ? toProject(doc) : null;
   }
 
@@ -109,7 +109,7 @@ export class MongoFindProjectsRepository extends FindProjectsRepository {
     userId: string,
   ): Promise<ProjectRole | null> {
     const doc = await this.projects
-      .findOne({ _id: projectId, memberIds: userId }, { members: 1 })
+      .findOne({ id: projectId, memberIds: userId }, { members: 1 })
       .lean<Pick<ProjectDoc, 'members'>>();
     return doc?.members.find((m) => m.user.id === userId)?.role ?? null;
   }
@@ -124,7 +124,7 @@ export class MongoFindIssuesRepository extends FindIssuesRepository {
   }
 
   async findById(id: string): Promise<IssueReadModel | null> {
-    const doc = await this.issues.findById(id).lean<IssueDoc>();
+    const doc = await this.issues.findOne({ id: id }).lean<IssueDoc>();
     return doc ? issueFromDoc(doc) : null;
   }
 
@@ -136,7 +136,7 @@ export class MongoFindIssuesRepository extends FindIssuesRepository {
   async findByIds(ids: string[]): Promise<IssueReadModel[]> {
     if (ids.length === 0) return [];
     const docs = await this.issues
-      .find({ _id: { $in: ids } })
+      .find({ id: { $in: ids } })
       .lean<IssueDoc[]>();
     return docs.map(issueFromDoc);
   }
@@ -322,15 +322,15 @@ export class MongoFindIssuesRepository extends FindIssuesRepository {
     // Only the top of each tree: a ticket with subtasks under an epic is not one.
     const docs = await this.issues
       .find({
-        _id: { $in: [...progress.keys()] },
+        id: { $in: [...progress.keys()] },
         'parent.id': null,
         trashedAt: null,
       })
       .sort({ number: 1 })
       .lean<IssueDoc[]>();
     return docs.map((doc) => {
-      const { _id: _ignored, ...row } = progress.get(doc._id) ?? {
-        _id: doc._id,
+      const { _id: _ignored, ...row } = progress.get(doc.id) ?? {
+        _id: doc.id,
         total: 0,
         finished: 0,
         storyPoints: 0,
@@ -456,7 +456,7 @@ export class MongoFindCommentsRepository extends FindCommentsRepository {
   }
 
   async findById(id: string): Promise<CommentReadModel | null> {
-    const doc = await this.comments.findById(id).lean<CommentDoc>();
+    const doc = await this.comments.findOne({ id: id }).lean<CommentDoc>();
     return doc ? commentFromDoc(doc) : null;
   }
 
@@ -496,7 +496,7 @@ export class MongoFindReleasesRepository extends FindReleasesRepository {
   }
 
   async findById(id: string): Promise<ReleaseReadModel | null> {
-    const doc = await this.releases.findById(id).lean<ReleaseDoc>();
+    const doc = await this.releases.findOne({ id: id }).lean<ReleaseDoc>();
     return doc ? fromDoc(doc) : null;
   }
 
diff --git a/libs/api/tracker/infrastructure/src/lib/mongo/git-integrations.repository.ts b/libs/api/tracker/infrastructure/src/lib/mongo/git-integrations.repository.ts
index d53d230..451e0cf 100644
--- a/libs/api/tracker/infrastructure/src/lib/mongo/git-integrations.repository.ts
+++ b/libs/api/tracker/infrastructure/src/lib/mongo/git-integrations.repository.ts
@@ -21,7 +21,7 @@ export class MongoGitIntegrationsRepository extends GitIntegrationsRepository {
 
   async repositoriesOf(projectId: string): Promise<GitRepositoryConfig[]> {
     const doc = await this.integrations
-      .findById(projectId)
+      .findOne({ id: projectId })
       .lean<GitIntegrationDoc>();
     if (!doc) return [];
     if (doc.repositories) return doc.repositories;
@@ -44,11 +44,11 @@ export class MongoGitIntegrationsRepository extends GitIntegrationsRepository {
     repositories: GitRepositoryConfig[],
   ): Promise<void> {
     if (!repositories.length) {
-      await this.integrations.deleteOne({ _id: projectId });
+      await this.integrations.deleteOne({ id: projectId });
       return;
     }
     await this.integrations.updateOne(
-      { _id: projectId },
+      { id: projectId },
       { $set: { repositories }, $unset: { secret: '', createdAt: '' } },
       { upsert: true },
     );
diff --git a/libs/api/tracker/infrastructure/src/lib/mongo/notifications.repository.ts b/libs/api/tracker/infrastructure/src/lib/mongo/notifications.repository.ts
index a0c2d62..f7a8325 100644
--- a/libs/api/tracker/infrastructure/src/lib/mongo/notifications.repository.ts
+++ b/libs/api/tracker/infrastructure/src/lib/mongo/notifications.repository.ts
@@ -26,7 +26,7 @@ export class MongoNotificationsRepository extends NotificationsRepository {
 
   async insert({ id, ...rest }: NotificationReadModel): Promise<boolean> {
     const result = await this.notifications.updateOne(
-      { _id: id },
+      { id },
       { $setOnInsert: rest },
       { upsert: true },
     );
@@ -51,21 +51,21 @@ export class MongoNotificationsRepository extends NotificationsRepository {
 
   async markRead(userId: string, ids: string[] | null): Promise<void> {
     await this.notifications.updateMany(
-      { userId, readAt: null, ...(ids ? { _id: { $in: ids } } : {}) },
+      { userId, readAt: null, ...(ids ? { id: { $in: ids } } : {}) },
       { $set: { readAt: new Date().toISOString() } },
     );
   }
 
   async settings(userId: string): Promise<NotificationSettingsReadModel> {
     const doc = await this.settingsDocs
-      .findById(userId)
+      .findOne({ id: userId })
       .lean<NotificationSettingsDoc>();
     return { userId, email: doc?.email ?? false };
   }
 
   async saveSettings(settings: NotificationSettingsReadModel): Promise<void> {
     await this.settingsDocs.updateOne(
-      { _id: settings.userId },
+      { id: settings.userId },
       { $set: { email: settings.email } },
       { upsert: true },
     );
diff --git a/libs/api/tracker/infrastructure/src/lib/mongo/outgoing-webhooks.repository.ts b/libs/api/tracker/infrastructure/src/lib/mongo/outgoing-webhooks.repository.ts
index e14097c..2083ed2 100644
--- a/libs/api/tracker/infrastructure/src/lib/mongo/outgoing-webhooks.repository.ts
+++ b/libs/api/tracker/infrastructure/src/lib/mongo/outgoing-webhooks.repository.ts
@@ -33,12 +33,14 @@ export class MongoOutgoingWebhooksRepository extends OutgoingWebhooksRepository
   }
 
   async findById(id: string): Promise<OutgoingWebhook | null> {
-    const doc = await this.webhooks.findById(id).lean<OutgoingWebhookDoc>();
+    const doc = await this.webhooks
+      .findOne({ id: id })
+      .lean<OutgoingWebhookDoc>();
     return doc ? (fromDoc(doc) as OutgoingWebhook) : null;
   }
 
   async insert({ id, ...rest }: OutgoingWebhook): Promise<void> {
-    await this.webhooks.create({ _id: id, ...rest });
+    await this.webhooks.create({ id, ...rest });
   }
 
   async update(
@@ -46,17 +48,14 @@ export class MongoOutgoingWebhooksRepository extends OutgoingWebhooksRepository
     changes: Partial<Pick<OutgoingWebhook, 'url' | 'events' | 'active'>>,
   ): Promise<void> {
     if (Object.keys(changes).length)
-      await this.webhooks.updateOne({ _id: id }, { $set: changes });
+      await this.webhooks.updateOne({ id }, { $set: changes });
   }
 
   async delete(id: string): Promise<void> {
-    await this.webhooks.deleteOne({ _id: id });
+    await this.webhooks.deleteOne({ id });
   }
 
   async recordDelivery(id: string, delivery: WebhookDelivery): Promise<void> {
-    await this.webhooks.updateOne(
-      { _id: id },
-      { $set: { lastDelivery: delivery } },
-    );
+    await this.webhooks.updateOne({ id }, { $set: { lastDelivery: delivery } });
   }
 }
diff --git a/libs/api/tracker/infrastructure/src/lib/mongo/rank.backfill.ts b/libs/api/tracker/infrastructure/src/lib/mongo/rank.backfill.ts
index 3daf5c8..358f22b 100644
--- a/libs/api/tracker/infrastructure/src/lib/mongo/rank.backfill.ts
+++ b/libs/api/tracker/infrastructure/src/lib/mongo/rank.backfill.ts
@@ -18,13 +18,13 @@ export class RankBackfill implements OnApplicationBootstrap {
 
   async onApplicationBootstrap(): Promise<void> {
     const missing = await this.issues
-      .find({ rank: { $exists: false } }, { number: 1 })
-      .lean<Pick<IssueDoc, '_id' | 'number'>[]>();
+      .find({ rank: { $exists: false } }, { id: 1, number: 1 })
+      .lean<Pick<IssueDoc, 'id' | 'number'>[]>();
     if (missing.length === 0) return;
     const result = await this.issues.bulkWrite(
       missing.map((doc) => ({
         updateOne: {
-          filter: { _id: doc._id, rank: { $exists: false } },
+          filter: { id: doc.id, rank: { $exists: false } },
           update: { $set: { rank: implicitRank(doc.number) } },
         },
       })),
diff --git a/libs/api/tracker/infrastructure/src/lib/mongo/read-model.schemas.ts b/libs/api/tracker/infrastructure/src/lib/mongo/read-model.schemas.ts
index 9e1d34e..2e3f79b 100644
--- a/libs/api/tracker/infrastructure/src/lib/mongo/read-model.schemas.ts
+++ b/libs/api/tracker/infrastructure/src/lib/mongo/read-model.schemas.ts
@@ -15,11 +15,16 @@ import {
   SprintReadModel,
   implicitRank,
 } from '@task-stream/api/tracker/domain';
-import { Schema } from 'mongoose';
+import { Schema, Types } from 'mongoose';
 
 /* Read model (MongoDB): denormalised documents shaped for the GraphQL queries. */
 
-type Doc<T extends { id: string }> = Omit<T, 'id'> & { _id: string };
+/**
+ * Each document keeps the domain id (a uuid, the same one the event store
+ * uses) in `id`, unique; `_id` is Mongo's own ObjectId and means nothing
+ * outside the database.
+ */
+type Doc<T extends { id: string }> = T & { _id?: Types.ObjectId };
 
 export type ProjectDoc = Doc<ProjectReadModel> & { memberIds: string[] };
 /** Links are split: outward ones come from the issue itself, inward ones from other issues' events. */
@@ -34,11 +39,11 @@ export type ActivityDoc = Doc<ActivityReadModel>;
 export type TimelineDoc = Doc<IssueTimelineEntry>;
 export type NotificationDoc = Doc<NotificationReadModel>;
 export type SavedFilterDoc = Doc<SavedFilterReadModel>;
-export type OutgoingWebhookDoc = Omit<OutgoingWebhook, 'id'> & { _id: string };
-export type AutomationDoc = Omit<Automation, 'id'> & { _id: string };
+export type OutgoingWebhookDoc = Doc<OutgoingWebhook>;
+export type AutomationDoc = Doc<Automation>;
 export interface AutomationRunDoc {
   /** `ruleId:eventKey`: a rule runs once per event. */
-  _id: string;
+  id: string;
   at: Date;
 }
 export interface GitRepositoryDoc {
@@ -52,13 +57,15 @@ export interface GitRepositoryDoc {
  * kept: it reads as a repository named "principal" until the list is saved.
  */
 export interface GitIntegrationDoc {
-  _id: string;
+  /** The project's id. */
+  id: string;
   repositories?: GitRepositoryDoc[];
   secret?: string;
   createdAt?: string;
 }
 export interface NotificationSettingsDoc {
-  _id: string;
+  /** The user's id. */
+  id: string;
   email: boolean;
 }
 
@@ -88,11 +95,13 @@ const link = {
   issueId: String,
   issueKey: String,
 };
-const loose = { strict: false, versionKey: false, _id: false } as const;
+const loose = { strict: false, versionKey: false } as const;
+/** The domain id: what every query looks a document up by. */
+const domainId = { type: String, required: true, unique: true };
 
 export const ProjectSchema = new Schema<ProjectDoc>(
   {
-    _id: String,
+    id: domainId,
     key: { type: String, unique: true },
     isPublic: { type: Boolean, index: true },
     memberIds: { type: [String], index: true },
@@ -105,7 +114,7 @@ export const ProjectSchema = new Schema<ProjectDoc>(
 
 export const IssueSchema = new Schema<IssueDoc>(
   {
-    _id: String,
+    id: domainId,
     projectId: { type: String, index: true },
     key: { type: String, unique: true },
     status: String,
@@ -149,7 +158,7 @@ IssueSchema.index({ title: 'text', description: 'text', key: 'text' });
 
 export const CommentSchema = new Schema<CommentDoc>(
   {
-    _id: String,
+    id: domainId,
     issueId: { type: String, index: true },
     replyTo: { type: String, index: true },
     author: userRef,
@@ -160,13 +169,13 @@ export const CommentSchema = new Schema<CommentDoc>(
 CommentSchema.index({ issueId: 1, createdAt: 1 });
 
 export const ReleaseSchema = new Schema<ReleaseDoc>(
-  { _id: String, projectId: { type: String, index: true }, version: Number },
+  { id: domainId, projectId: { type: String, index: true }, version: Number },
   { ...loose, collection: 'releases_view' },
 );
 
 export const SprintSchema = new Schema<SprintDoc>(
   {
-    _id: String,
+    id: domainId,
     projectId: { type: String, index: true },
     status: String,
     version: Number,
@@ -176,7 +185,7 @@ export const SprintSchema = new Schema<SprintDoc>(
 
 export const ActivitySchema = new Schema<ActivityDoc>(
   {
-    _id: String,
+    id: domainId,
     projectId: String,
     issueId: String,
     actor: userRef,
@@ -188,14 +197,14 @@ ActivitySchema.index({ issueId: 1, occurredAt: -1 });
 
 /** Every status and release step of every ticket (statistics). */
 export const TimelineSchema = new Schema<TimelineDoc>(
-  { _id: String, projectId: String, issueId: String, at: String },
+  { id: domainId, projectId: String, issueId: String, at: String },
   { ...loose, collection: 'issue_timeline' },
 );
 TimelineSchema.index({ projectId: 1, at: 1 });
 
 export const NotificationSchema = new Schema<NotificationDoc>(
   {
-    _id: String,
+    id: domainId,
     userId: String,
     readAt: String,
     createdAt: String,
@@ -207,13 +216,13 @@ NotificationSchema.index({ userId: 1, createdAt: -1 });
 NotificationSchema.index({ userId: 1, readAt: 1 });
 
 export const NotificationSettingsSchema = new Schema<NotificationSettingsDoc>(
-  { _id: String, email: Boolean },
+  { id: domainId, email: Boolean },
   { ...loose, collection: 'notification_settings' },
 );
 
 export const SavedFilterSchema = new Schema<SavedFilterDoc>(
   {
-    _id: String,
+    id: domainId,
     projectId: String,
     owner: userRef,
     name: String,
@@ -226,13 +235,13 @@ SavedFilterSchema.index({ projectId: 1, 'owner.id': 1 });
 SavedFilterSchema.index({ projectId: 1, shared: 1 });
 
 export const GitIntegrationSchema = new Schema<GitIntegrationDoc>(
-  { _id: String, repositories: [Object], secret: String, createdAt: String },
+  { id: domainId, repositories: [Object], secret: String, createdAt: String },
   { ...loose, collection: 'git_integrations' },
 );
 
 export const OutgoingWebhookSchema = new Schema<OutgoingWebhookDoc>(
   {
-    _id: String,
+    id: domainId,
     projectId: { type: String, index: true },
     active: Boolean,
     events: [String],
@@ -244,7 +253,7 @@ export const OutgoingWebhookSchema = new Schema<OutgoingWebhookDoc>(
 
 export const AutomationSchema = new Schema<AutomationDoc>(
   {
-    _id: String,
+    id: domainId,
     projectId: { type: String, index: true },
     active: Boolean,
     createdBy: userRef,
@@ -254,7 +263,7 @@ export const AutomationSchema = new Schema<AutomationDoc>(
 );
 
 export const AutomationRunSchema = new Schema<AutomationRunDoc>(
-  { _id: String, at: Date },
+  { id: domainId, at: Date },
   { ...loose, collection: 'automation_runs' },
 );
 // Redeliveries happen within minutes; a month of memory is plenty.
@@ -277,17 +286,17 @@ export const READ_MODEL_SCHEMAS = [
   { name: ReadModels.SavedFilter, schema: SavedFilterSchema },
 ];
 
-export function fromDoc<T extends { _id: string }>(
-  doc: T,
-): Omit<T, '_id'> & { id: string } {
-  const { _id, ...rest } = doc;
-  return { id: _id, ...rest };
+/** A document as the model it holds: Mongo's own `_id` left out. */
+export function fromDoc<T extends { id: string }>(
+  doc: T & { _id?: unknown },
+): T {
+  const { _id: _ignored, ...rest } = doc;
+  return rest as T;
 }
 
 export function issueFromDoc(doc: IssueDoc): IssueReadModel {
-  const { _id, outwardLinks, inwardLinks, ...rest } = doc;
+  const { _id: _ignored, outwardLinks, inwardLinks, ...rest } = doc;
   return {
-    id: _id,
     ...rest,
     links: [...(outwardLinks ?? []), ...(inwardLinks ?? [])],
     // Tickets projected before attachments existed have none.
diff --git a/libs/api/tracker/infrastructure/src/lib/mongo/saved-filters.repository.ts b/libs/api/tracker/infrastructure/src/lib/mongo/saved-filters.repository.ts
index 54dabb4..32c178d 100644
--- a/libs/api/tracker/infrastructure/src/lib/mongo/saved-filters.repository.ts
+++ b/libs/api/tracker/infrastructure/src/lib/mongo/saved-filters.repository.ts
@@ -26,7 +26,7 @@ export class MongoSavedFiltersRepository extends SavedFiltersRepository {
   }
 
   async findById(id: string): Promise<SavedFilterReadModel | null> {
-    const doc = await this.filters.findById(id).lean<SavedFilterDoc>();
+    const doc = await this.filters.findOne({ id: id }).lean<SavedFilterDoc>();
     return doc ? toFilter(doc) : null;
   }
 
@@ -35,11 +35,11 @@ export class MongoSavedFiltersRepository extends SavedFiltersRepository {
   }
 
   async insert({ id, ...rest }: SavedFilterReadModel): Promise<void> {
-    await this.filters.create({ _id: id, ...rest });
+    await this.filters.create({ id, ...rest });
   }
 
   async delete(id: string): Promise<void> {
-    await this.filters.deleteOne({ _id: id });
+    await this.filters.deleteOne({ id });
   }
 }
 
diff --git a/libs/api/tracker/infrastructure/src/lib/mongo/sprints.repositories.ts b/libs/api/tracker/infrastructure/src/lib/mongo/sprints.repositories.ts
index 5fcccd4..fc5e614 100644
--- a/libs/api/tracker/infrastructure/src/lib/mongo/sprints.repositories.ts
+++ b/libs/api/tracker/infrastructure/src/lib/mongo/sprints.repositories.ts
@@ -24,7 +24,7 @@ export class MongoFindSprintsRepository extends FindSprintsRepository {
   }
 
   async findById(id: string): Promise<SprintReadModel | null> {
-    const doc = await this.sprints.findById(id).lean<SprintDoc>();
+    const doc = await this.sprints.findOne({ id: id }).lean<SprintDoc>();
     return doc ? fromDoc(doc) : null;
   }
 
@@ -67,6 +67,6 @@ export class MongoUpsertMaterializedSprintRepository extends UpsertMaterializedS
   }
 
   async remove(sprintId: string) {
-    await this.sprints.deleteOne({ _id: sprintId });
+    await this.sprints.deleteOne({ id: sprintId });
   }
 }
diff --git a/libs/api/tracker/infrastructure/src/lib/mongo/status-category.backfill.ts b/libs/api/tracker/infrastructure/src/lib/mongo/status-category.backfill.ts
index 23f10a1..97f945c 100644
--- a/libs/api/tracker/infrastructure/src/lib/mongo/status-category.backfill.ts
+++ b/libs/api/tracker/infrastructure/src/lib/mongo/status-category.backfill.ts
@@ -30,11 +30,11 @@ export class StatusCategoryBackfill implements OnApplicationBootstrap {
 
     const projectIds = [...new Set(groups.map((g) => g._id.projectId))];
     const projects = await this.projects
-      .find({ _id: { $in: projectIds } }, { settings: 1 })
-      .lean<Pick<ProjectDoc, '_id' | 'settings'>[]>();
+      .find({ id: { $in: projectIds } }, { id: 1, settings: 1 })
+      .lean<Pick<ProjectDoc, 'id' | 'settings'>[]>();
     const workflows = new Map(
       projects.map((p) => [
-        p._id,
+        p.id,
         p.settings
           ? new ProjectWorkflow(p.settings)
           : ProjectWorkflow.default(),
diff --git a/libs/api/tracker/infrastructure/src/lib/mongo/upsert-if-newer.ts b/libs/api/tracker/infrastructure/src/lib/mongo/upsert-if-newer.ts
index dbbf795..5de41dc 100644
--- a/libs/api/tracker/infrastructure/src/lib/mongo/upsert-if-newer.ts
+++ b/libs/api/tracker/infrastructure/src/lib/mongo/upsert-if-newer.ts
@@ -4,7 +4,7 @@ import { Model } from 'mongoose';
  * Idempotent upsert: only applies a change carrying a newer aggregate
  * version (event position). Redelivered events become no-ops.
  */
-export async function upsertIfNewer<T extends { _id: string }>(
+export async function upsertIfNewer<T extends { id: string }>(
   model: Model<T>,
   id: string,
   version: number,
@@ -13,13 +13,13 @@ export async function upsertIfNewer<T extends { _id: string }>(
 ): Promise<boolean> {
   try {
     const result = await model.updateOne(
-      { _id: id, version: { $lt: version } } as never,
+      { id, version: { $lt: version } } as never,
       { $set: { ...set, version }, $setOnInsert: setOnInsert } as never,
       { upsert: true },
     );
     return result.modifiedCount + result.upsertedCount > 0;
   } catch (error) {
-    // Duplicate _id on upsert: the stored document is already newer.
+    // Duplicate id on upsert: the stored document is already newer.
     if ((error as { code?: number }).code === 11000) return false;
     throw error;
   }
diff --git a/libs/api/tracker/infrastructure/src/lib/mongo/upsert-materialized.repositories.ts b/libs/api/tracker/infrastructure/src/lib/mongo/upsert-materialized.repositories.ts
index 3c1bf74..28dbf39 100644
--- a/libs/api/tracker/infrastructure/src/lib/mongo/upsert-materialized.repositories.ts
+++ b/libs/api/tracker/infrastructure/src/lib/mongo/upsert-materialized.repositories.ts
@@ -64,12 +64,12 @@ export class MongoUpsertMaterializedProjectRepository extends UpsertMaterialized
 
   async remove(projectId: string) {
     await Promise.all([
-      this.projects.deleteOne({ _id: projectId }),
+      this.projects.deleteOne({ id: projectId }),
       this.activity.deleteMany({ projectId }),
       this.timeline.deleteMany({ projectId }),
       // Views of the board of a project that is gone.
       this.savedFilters.deleteMany({ projectId }),
-      this.gitIntegrations.deleteOne({ _id: projectId }),
+      this.gitIntegrations.deleteOne({ id: projectId }),
       this.outgoingWebhooks.deleteMany({ projectId }),
       this.automations.deleteMany({ projectId }),
     ]);
@@ -102,7 +102,7 @@ export class MongoUpsertMaterializedIssueRepository extends UpsertMaterializedIs
 
   async remove(issueId: string) {
     await Promise.all([
-      this.issues.deleteOne({ _id: issueId }),
+      this.issues.deleteOne({ id: issueId }),
       this.issues.updateMany(
         {
           $or: [
@@ -138,21 +138,21 @@ export class MongoUpsertMaterializedIssueRepository extends UpsertMaterializedIs
 
   async addWatcher(issueId: string, user: UserRefReadModel) {
     await this.issues.updateOne(
-      { _id: issueId, 'watchers.id': { $ne: user.id } },
+      { id: issueId, 'watchers.id': { $ne: user.id } },
       { $push: { watchers: user } },
     );
   }
 
   async removeWatcher(issueId: string, userId: string) {
     await this.issues.updateOne(
-      { _id: issueId },
+      { id: issueId },
       { $pull: { watchers: { id: userId } } },
     );
   }
 
   async addChecklistItem(issueId: string, item: ChecklistItemReadModel) {
     await this.issues.updateOne(
-      { _id: issueId, 'checklist.id': { $ne: item.id } },
+      { id: issueId, 'checklist.id': { $ne: item.id } },
       { $push: { checklist: item } },
     );
   }
@@ -170,14 +170,14 @@ export class MongoUpsertMaterializedIssueRepository extends UpsertMaterializedIs
     );
     if (Object.keys(set).length === 0) return;
     await this.issues.updateOne(
-      { _id: issueId, 'checklist.id': itemId },
+      { id: issueId, 'checklist.id': itemId },
       { $set: set },
     );
   }
 
   async removeChecklistItem(issueId: string, itemId: string) {
     await this.issues.updateOne(
-      { _id: issueId },
+      { id: issueId },
       { $pull: { checklist: { id: itemId } } },
     );
   }
@@ -185,11 +185,11 @@ export class MongoUpsertMaterializedIssueRepository extends UpsertMaterializedIs
   async putDevLink(issueId: string, link: DevLink) {
     // Same URL: the newer report replaces the older one.
     await this.issues.updateOne(
-      { _id: issueId },
+      { id: issueId },
       { $pull: { devLinks: { url: link.url } } },
     );
     await this.issues.updateOne(
-      { _id: issueId },
+      { id: issueId },
       { $push: { devLinks: { $each: [link], $slice: -MAX_DEV_LINKS } } },
     );
   }
@@ -203,14 +203,14 @@ export class MongoUpsertMaterializedIssueRepository extends UpsertMaterializedIs
 
   async addAttachment(issueId: string, attachment: AttachmentReadModel) {
     await this.issues.updateOne(
-      { _id: issueId, 'attachments.id': { $ne: attachment.id } },
+      { id: issueId, 'attachments.id': { $ne: attachment.id } },
       { $push: { attachments: attachment } },
     );
   }
 
   async removeAttachment(issueId: string, attachmentId: string) {
     await this.issues.updateOne(
-      { _id: issueId },
+      { id: issueId },
       { $pull: { attachments: { id: attachmentId } } },
     );
   }
@@ -219,7 +219,7 @@ export class MongoUpsertMaterializedIssueRepository extends UpsertMaterializedIs
     const field = link.direction === 'OUTWARD' ? 'outwardLinks' : 'inwardLinks';
     await this.issues.updateOne(
       {
-        _id: issueId,
+        id: issueId,
         [field]: {
           $not: { $elemMatch: { type: link.type, issueId: link.issueId } },
         },
@@ -234,13 +234,13 @@ export class MongoUpsertMaterializedIssueRepository extends UpsertMaterializedIs
   ) {
     const field = link.direction === 'OUTWARD' ? 'outwardLinks' : 'inwardLinks';
     await this.issues.updateOne(
-      { _id: issueId },
+      { id: issueId },
       { $pull: { [field]: { type: link.type, issueId: link.issueId } } },
     );
   }
 
   async setCommentCount(issueId: string, commentCount: number) {
-    await this.issues.updateOne({ _id: issueId }, { $set: { commentCount } });
+    await this.issues.updateOne({ id: issueId }, { $set: { commentCount } });
   }
 
   async recategorize(
@@ -289,7 +289,7 @@ export class MongoUpsertMaterializedCommentRepository extends UpsertMaterialized
   }
 
   async remove(id: string) {
-    await this.comments.deleteOne({ _id: id });
+    await this.comments.deleteOne({ id });
   }
 }
 
@@ -311,7 +311,7 @@ export class MongoUpsertMaterializedReleaseRepository extends UpsertMaterialized
   }
 
   async remove(releaseId: string) {
-    await this.releases.deleteOne({ _id: releaseId });
+    await this.releases.deleteOne({ id: releaseId });
   }
 }
 
@@ -326,7 +326,7 @@ export class MongoUpsertMaterializedActivityRepository extends UpsertMaterialize
 
   async insert({ id, ...fields }: ActivityReadModel): Promise<boolean> {
     const result = await this.activity.updateOne(
-      { _id: id },
+      { id },
       { $setOnInsert: fields },
       { upsert: true },
     );
@@ -345,7 +345,7 @@ export class MongoUpsertMaterializedTimelineRepository extends UpsertMaterialize
 
   async record({ id, ...fields }: IssueTimelineEntry): Promise<void> {
     await this.timeline.updateOne(
-      { _id: id },
+      { id },
       { $setOnInsert: fields },
       { upsert: true },
     );
diff --git a/libs/api/tracker/infrastructure/src/lib/postgres/lookup.entities.ts b/libs/api/tracker/infrastructure/src/lib/postgres/lookup.entities.ts
index 24fd5b4..196ea71 100644
--- a/libs/api/tracker/infrastructure/src/lib/postgres/lookup.entities.ts
+++ b/libs/api/tracker/infrastructure/src/lib/postgres/lookup.entities.ts
@@ -1,13 +1,18 @@
-import { Column, Entity, PrimaryColumn } from 'typeorm';
+import { Column, Entity, Index, PrimaryGeneratedColumn, Unique } from 'typeorm';
 
 /*
  * Write-side lookup tables. The event store holds the truth; these only
  * enforce uniqueness and sequences that cannot be checked per aggregate.
+ * Each row has a uuid `id`; what makes it unique is a constraint apart.
  */
 
 @Entity('project_keys')
 export class ProjectKeyEntity {
-  @PrimaryColumn({ length: 10 })
+  @PrimaryGeneratedColumn('uuid')
+  id!: string;
+
+  @Index('uq_project_keys_key', { unique: true })
+  @Column({ length: 10 })
   key!: string;
 
   @Column({ name: 'project_id', length: 64 })
@@ -16,7 +21,12 @@ export class ProjectKeyEntity {
 
 @Entity('issue_sequences')
 export class IssueSequenceEntity {
-  @PrimaryColumn({ name: 'project_id', length: 64 })
+  @PrimaryGeneratedColumn('uuid')
+  id!: string;
+
+  /** `ON CONFLICT (project_id)` counts on it. */
+  @Index('uq_issue_sequences_project', { unique: true })
+  @Column({ name: 'project_id', length: 64 })
   projectId!: string;
 
   @Column({ name: 'last_number', type: 'int', default: 0 })
@@ -24,11 +34,15 @@ export class IssueSequenceEntity {
 }
 
 @Entity('release_names')
+@Unique('uq_release_names_project_name', ['projectId', 'name'])
 export class ReleaseNameEntity {
-  @PrimaryColumn({ name: 'project_id', length: 64 })
+  @PrimaryGeneratedColumn('uuid')
+  id!: string;
+
+  @Column({ name: 'project_id', length: 64 })
   projectId!: string;
 
-  @PrimaryColumn({ length: 60 })
+  @Column({ length: 60 })
   name!: string;
 
   @Column({ name: 'release_id', length: 64 })
diff --git a/libs/web/tracker/application/src/lib/facades/issue.facade.ts b/libs/web/tracker/application/src/lib/facades/issue.facade.ts
index 7c87028..3fcffd4 100644
--- a/libs/web/tracker/application/src/lib/facades/issue.facade.ts
+++ b/libs/web/tracker/application/src/lib/facades/issue.facade.ts
@@ -6,6 +6,7 @@ import {
   IssueLink,
   IssuesGateway,
   IssueLinkType,
+  IssueSummary,
   UpdateIssueInput,
 } from '@task-stream/web/tracker/domain';
 import { map, Observable } from 'rxjs';
@@ -120,6 +121,20 @@ export class IssueFacade {
   }
 
   /** Places the open ticket under another one by its key; null: back to the top. */
+  /**
+   * Tickets to link to or hang the open one from: the most recently updated
+   * of all my projects (links may cross projects), the open one aside.
+   */
+  candidates(): Observable<IssueSummary[]> {
+    return this.issues
+      .mine({ assignedToMe: false, limit: 200 })
+      .pipe(
+        map((page) =>
+          page.items.filter((item) => item.id !== this.store.issue()?.id),
+        ),
+      );
+  }
+
   setParent(parentKey: string | null): void {
     this.withIssue((issueId) =>
       this.dispatch.parentRequested({ issueId, parentKey }),
diff --git a/libs/web/tracker/presenters/src/lib/pages/backlog.page.ts b/libs/web/tracker/presenters/src/lib/pages/backlog.page.ts
index e9b39a1..f110485 100644
--- a/libs/web/tracker/presenters/src/lib/pages/backlog.page.ts
+++ b/libs/web/tracker/presenters/src/lib/pages/backlog.page.ts
@@ -10,6 +10,7 @@ import {
 } from '@angular/core';
 import { RouterLink } from '@angular/router';
 import {
+  PiCheckboxComponent,
   PiEmptyStateComponent,
   PiIconButtonComponent,
   PiIconComponent,
@@ -34,6 +35,7 @@ import { initials, PRIORITY, statusLook, typeLook } from '../ui/copy';
   selector: 'ts-backlog-page',
   changeDetection: ChangeDetectionStrategy.OnPush,
   imports: [
+    PiCheckboxComponent,
     BulkBarComponent,
     RouterLink,
     CdkDrag,
@@ -96,14 +98,15 @@ import { initials, PRIORITY, statusLook, typeLook } from '../ui/copy';
             [cdkDragData]="issue"
             [class.is-selected]="selected().has(issue.id)"
           >
-            <input
-              type="checkbox"
+            <pi-checkbox
               class="ts-backlog__pick"
-              [attr.aria-label]="'Seleccionar ' + issue.key"
               [disabled]="!project.canContribute()"
               [checked]="selected().has(issue.id)"
-              (change)="toggle(issue.id, $any($event.target).checked)"
-            />
+              (checkedChange)="toggle(issue.id, $event)"
+              ><span class="visually-hidden"
+                >Seleccionar {{ issue.key }}</span
+              ></pi-checkbox
+            >
             <span class="ts-backlog__pos ts-mono">{{ i + 1 }}</span>
             <span
               class="ts-backlog__type"
diff --git a/libs/web/tracker/presenters/src/lib/pages/issue.page.ts b/libs/web/tracker/presenters/src/lib/pages/issue.page.ts
index 090d2dc..f51a26f 100644
--- a/libs/web/tracker/presenters/src/lib/pages/issue.page.ts
+++ b/libs/web/tracker/presenters/src/lib/pages/issue.page.ts
@@ -11,7 +11,9 @@ import {
   TemplateRef,
   viewChild,
 } from '@angular/core';
+import { toObservable, toSignal } from '@angular/core/rxjs-interop';
 import { form, FormField, required } from '@angular/forms/signals';
+import { catchError, distinctUntilChanged, filter, of, switchMap } from 'rxjs';
 import { ActivatedRoute, Router, RouterLink } from '@angular/router';
 import {
   PiActionButtonComponent,
@@ -23,6 +25,7 @@ import {
   PiLabelDirective,
   PiNoteComponent,
   PiProgressBarComponent,
+  PiSearchableSelectFieldComponent,
   PiSelectFieldComponent,
   PiSkeletonComponent,
   PiTextareaComponent,
@@ -93,6 +96,7 @@ const MAX_FILE_BYTES = 25 * 1024 * 1024;
     PiLabelDirective,
     PiNoteComponent,
     PiProgressBarComponent,
+    PiSearchableSelectFieldComponent,
     PiSelectFieldComponent,
     PiSkeletonComponent,
     PiTextFieldComponent,
@@ -404,8 +408,11 @@ const MAX_FILE_BYTES = 25 * 1024 * 1024;
                     (submit)="$event.preventDefault(); setParent()"
                     novalidate
                   >
-                    <pi-text-field
-                      placeholder="Colgar de… (clave de la épica, p. ej. WEB-3)"
+                    <pi-searchable-select-field
+                      placeholder="Colgar de… (la épica o el ticket padre)"
+                      searchPlaceholder="Busca por clave o título"
+                      emptyLabel="Ningún ticket de este proyecto coincide"
+                      [options]="parentOptions()"
                       [(value)]="parentKey"
                     />
                     <pi-action-button
@@ -413,7 +420,7 @@ const MAX_FILE_BYTES = 25 * 1024 * 1024;
                       color="grey"
                       appearance="outline"
                       text="Colgar"
-                      [disabled]="!parentKey().trim()"
+                      [disabled]="!parentKey()"
                       (execute)="setParent()"
                     />
                   </form>
@@ -512,15 +519,18 @@ const MAX_FILE_BYTES = 25 * 1024 * 1024;
                   [options]="linkTypeOptions"
                   [(value)]="linkType"
                 />
-                <pi-text-field
-                  placeholder="Clave, p. ej. BE-3"
+                <pi-searchable-select-field
+                  placeholder="Elige el ticket"
+                  searchPlaceholder="Busca por clave o título"
+                  emptyLabel="Ningún ticket coincide"
+                  [options]="linkOptions()"
                   [(value)]="linkTarget"
                 />
                 <pi-action-button
                   size="small"
                   color="primary"
                   text="Relacionar"
-                  [disabled]="!linkTarget().trim()"
+                  [disabled]="!linkTarget()"
                   (execute)="link()"
                 />
               </form>
@@ -1066,7 +1076,33 @@ export class IssuePage {
 
   // Inline forms: plain signals (a required validator would flag them red right after submitting).
   protected readonly linkType = signal<string | null>(IssueLinkType.RELATES_TO);
-  protected readonly linkTarget = signal('');
+  protected readonly linkTarget = signal<string | null>(null);
+  /** Tickets of my projects, to pick from instead of typing a key. */
+  private readonly candidates = toSignal(
+    toObservable(computed(() => this.facade.issue()?.id ?? null)).pipe(
+      filter((id): id is string => !!id),
+      distinctUntilChanged(),
+      switchMap(() => this.facade.candidates().pipe(catchError(() => of([])))),
+    ),
+    { initialValue: [] },
+  );
+  /** Any of them: links may cross projects (FE ↔ BE ↔ QA). */
+  protected readonly linkOptions = computed(() =>
+    this.candidates().map((issue) => ({
+      value: issue.key,
+      label: `${issue.key} · ${issue.title}`,
+    })),
+  );
+  /** Only this project's: a ticket hangs from one of its own. */
+  protected readonly parentOptions = computed(() => {
+    const projectId = this.facade.issue()?.projectId;
+    return this.candidates()
+      .filter((issue) => issue.projectId === projectId)
+      .map((issue) => ({
+        value: issue.key,
+        label: `${issue.key} · ${issue.title}`,
+      }));
+  });
   protected readonly commentBody = signal('');
   /** The comment being answered, and the answer being written. */
   protected readonly replyingTo = signal<string | null>(null);
@@ -1133,7 +1169,7 @@ export class IssuePage {
   protected readonly checklistText = signal('');
   protected readonly subtaskTitle = signal('');
   protected readonly subtaskType = signal<string | null>(null);
-  protected readonly parentKey = signal('');
+  protected readonly parentKey = signal<string | null>(null);
   /** Active types; subtasks start as tasks when the project has them. */
   protected readonly subtaskTypeOptions = computed<
     PiSelectFieldOption<string>[]
@@ -1227,10 +1263,10 @@ export class IssuePage {
   }
 
   protected setParent(): void {
-    const key = this.parentKey().trim();
+    const key = this.parentKey();
     if (!key) return;
     this.facade.setParent(key);
-    this.parentKey.set('');
+    this.parentKey.set(null);
   }
 
   protected move(to: string): void {
@@ -1283,13 +1319,13 @@ export class IssuePage {
   }
 
   protected link(): void {
-    const targetKey = this.linkTarget().trim();
+    const targetKey = this.linkTarget();
     if (!targetKey) return;
     this.facade.link(
       (this.linkType() ?? IssueLinkType.RELATES_TO) as IssueLinkType,
       targetKey,
     );
-    this.linkTarget.set('');
+    this.linkTarget.set(null);
   }
 
   protected unlink(link: IssueLink): void {
diff --git a/libs/web/tracker/presenters/src/lib/pages/list.page.ts b/libs/web/tracker/presenters/src/lib/pages/list.page.ts
index e63ab99..6c6ab53 100644
--- a/libs/web/tracker/presenters/src/lib/pages/list.page.ts
+++ b/libs/web/tracker/presenters/src/lib/pages/list.page.ts
@@ -9,6 +9,7 @@ import {
 } from '@angular/core';
 import { RouterLink } from '@angular/router';
 import {
+  PiCheckboxComponent,
   PiEmptyStateComponent,
   PiIconComponent,
   PiNoteComponent,
@@ -78,6 +79,7 @@ const numberOf = (key: string) => Number(key.split('-').pop());
   selector: 'ts-list-page',
   changeDetection: ChangeDetectionStrategy.OnPush,
   imports: [
+    PiCheckboxComponent,
     BlockedComponent,
     BulkBarComponent,
     VoteComponent,
@@ -165,12 +167,13 @@ const numberOf = (key: string) => Number(key.split('-').pop());
               <tr [class.is-selected]="selected().has(issue.id)">
                 @if (project.canContribute()) {
                   <td class="ts-list__pick">
-                    <input
-                      type="checkbox"
-                      [attr.aria-label]="'Seleccionar ' + issue.key"
+                    <pi-checkbox
                       [checked]="selected().has(issue.id)"
-                      (change)="toggle(issue.id, $any($event.target).checked)"
-                    />
+                      (checkedChange)="toggle(issue.id, $event)"
+                      ><span class="visually-hidden"
+                        >Seleccionar {{ issue.key }}</span
+                      ></pi-checkbox
+                    >
                   </td>
                 }
                 <td class="ts-list__key">
diff --git a/libs/web/tracker/presenters/src/lib/pages/projects.page.ts b/libs/web/tracker/presenters/src/lib/pages/projects.page.ts
index ba1d95d..6cde1ee 100644
--- a/libs/web/tracker/presenters/src/lib/pages/projects.page.ts
+++ b/libs/web/tracker/presenters/src/lib/pages/projects.page.ts
@@ -17,6 +17,7 @@ import {
 } from '@angular/forms/signals';
 import {
   PiActionButtonComponent,
+  PiCheckboxComponent,
   PiEmptyStateComponent,
   PiLabelDirective,
   PiSkeletonComponent,
@@ -34,6 +35,7 @@ import { MyWorkComponent } from './my-work';
   selector: 'ts-projects-page',
   changeDetection: ChangeDetectionStrategy.OnPush,
   imports: [
+    PiCheckboxComponent,
     FormField,
     GoToComponent,
     ProjectCardComponent,
@@ -123,14 +125,13 @@ import { MyWorkComponent } from './my-work';
         >
           <pi-label>Descripción</pi-label>
         </pi-textarea>
-        <label class="ts-public-check">
-          <input type="checkbox" [formField]="f.isPublic" />
-          <span>
-            <strong>Proyecto público</strong>
+        <div class="ts-public-check">
+          <pi-checkbox label="Proyecto público" [formField]="f.isPublic" />
+          <p>
             Cualquiera, también sin iniciar sesión, podrá verlo (solo lectura).
             Se puede cambiar después en Configuración.
-          </span>
-        </label>
+          </p>
+        </div>
         <pi-action-button
           size="w100"
           color="primary"
@@ -164,22 +165,11 @@ import { MyWorkComponent } from './my-work';
       }
     }
     .ts-public-check {
-      display: flex;
-      align-items: flex-start;
-      gap: 0.625rem;
-      font-size: 0.8125rem;
-      color: var(--ts-muted);
-      cursor: pointer;
-      input {
-        width: 1rem;
-        height: 1rem;
-        margin-top: 0.125rem;
-        accent-color: var(--ts-brand);
-      }
-      strong {
-        display: block;
-        color: var(--ts-ink);
-        font-size: 0.875rem;
+      p {
+        /* Under the checkbox's text, past the box. */
+        margin: 0 0 0 2.5rem;
+        color: var(--ts-muted);
+        font-size: 0.8125rem;
       }
     }
     .ts-projects {
diff --git a/libs/web/tracker/presenters/src/lib/pages/settings.page.ts b/libs/web/tracker/presenters/src/lib/pages/settings.page.ts
index 6805329..d7479e9 100644
--- a/libs/web/tracker/presenters/src/lib/pages/settings.page.ts
+++ b/libs/web/tracker/presenters/src/lib/pages/settings.page.ts
@@ -16,7 +16,7 @@ import {
   untracked,
 } from '@angular/core';
 import { NgTemplateOutlet } from '@angular/common';
-import { PiIconComponent, PiNoteComponent } from '@pi/ui';
+import { PiCheckboxComponent, PiIconComponent, PiNoteComponent } from '@pi/ui';
 import { GitIntegrationComponent } from '../ui/git-integration';
 import { WebhooksComponent } from '../ui/webhooks';
 import { TransferComponent } from '../ui/transfer';
@@ -57,6 +57,7 @@ function idFrom(name: string): string {
   selector: 'ts-settings-page',
   changeDetection: ChangeDetectionStrategy.OnPush,
   imports: [
+    PiCheckboxComponent,
     RouterLink,
     GitIntegrationComponent,
     WebhooksComponent,
@@ -263,18 +264,16 @@ function idFrom(name: string): string {
                       })
                     "
                   />
-                  <label class="ts-check">
-                    <input
-                      type="checkbox"
-                      [checked]="status.requiresReason"
-                      (change)="
-                        edit('statuses', i, {
-                          requiresReason: $any($event.target).checked,
-                        })
-                      "
-                    />
-                    <span class="visually-hidden">Pide motivo</span>
-                  </label>
+                  <pi-checkbox
+                    class="ts-check"
+                    [checked]="status.requiresReason"
+                    (checkedChange)="
+                      edit('statuses', i, { requiresReason: $event })
+                    "
+                    ><span class="visually-hidden"
+                      >Pide motivo</span
+                    ></pi-checkbox
+                  >
                   <ng-container
                     [ngTemplateOutlet]="archive"
                     [ngTemplateOutletContext]="{
@@ -330,18 +329,15 @@ function idFrom(name: string): string {
                       @for (to of activeStatuses(); track to.id) {
                         <td>
                           @if (from.id !== to.id) {
-                            <input
-                              type="checkbox"
-                              [attr.aria-label]="from.name + ' → ' + to.name"
+                            <pi-checkbox
                               [checked]="allows(from.id, to.id)"
-                              (change)="
-                                toggleTransition(
-                                  from.id,
-                                  to.id,
-                                  $any($event.target).checked
-                                )
+                              (checkedChange)="
+                                toggleTransition(from.id, to.id, $event)
                               "
-                            />
+                              ><span class="visually-hidden"
+                                >{{ from.name }} → {{ to.name }}</span
+                              ></pi-checkbox
+                            >
                           }
                         </td>
                       }
diff --git a/libs/web/tracker/presenters/src/lib/ui/bulk-bar.ts b/libs/web/tracker/presenters/src/lib/ui/bulk-bar.ts
index a8910fe..5f40f47 100644
--- a/libs/web/tracker/presenters/src/lib/ui/bulk-bar.ts
+++ b/libs/web/tracker/presenters/src/lib/ui/bulk-bar.ts
@@ -9,6 +9,7 @@ import {
 } from '@angular/core';
 import {
   PiActionButtonComponent,
+  PiCheckboxComponent,
   PiSelectFieldComponent,
   PiTextFieldComponent,
   type PiSelectFieldOption,
@@ -29,21 +30,26 @@ const NOBODY = '__none__';
   selector: 'ts-bulk-bar',
   changeDetection: ChangeDetectionStrategy.OnPush,
   imports: [
+    PiCheckboxComponent,
     PiActionButtonComponent,
     PiSelectFieldComponent,
     PiTextFieldComponent,
   ],
   template: `
     <div class="ts-bulk" role="toolbar" aria-label="Edición en bloque">
-      <label class="ts-bulk__all">
-        <input
-          type="checkbox"
-          [checked]="allSelected()"
-          [indeterminate]="count() > 0 && !allSelected()"
-          (change)="selectAll.emit($any($event.target).checked)"
-        />
-        {{ count() ? count() + ' seleccionados' : 'Seleccionar todos' }}
-      </label>
+      <pi-checkbox
+        class="ts-bulk__all"
+        [checked]="allSelected()"
+        [indeterminate]="count() > 0 && !allSelected()"
+        [label]="
+          count() === 1
+            ? '1 seleccionado'
+            : count()
+              ? count() + ' seleccionados'
+              : 'Seleccionar todos'
+        "
+        (checkedChange)="selectAll.emit($event)"
+      />
       @if (count()) {
         <pi-select-field [options]="fields" [(value)]="field" />
         @switch (field()) {
diff --git a/libs/web/tracker/presenters/src/lib/ui/webhooks.ts b/libs/web/tracker/presenters/src/lib/ui/webhooks.ts
index 48187ff..138a173 100644
--- a/libs/web/tracker/presenters/src/lib/ui/webhooks.ts
+++ b/libs/web/tracker/presenters/src/lib/ui/webhooks.ts
@@ -9,7 +9,7 @@ import {
   untracked,
 } from '@angular/core';
 import { takeUntilDestroyed } from '@angular/core/rxjs-interop';
-import { PiTextFieldComponent } from '@pi/ui';
+import { PiCheckboxComponent, PiTextFieldComponent } from '@pi/ui';
 import { ToastService } from '@task-stream/web/shared/ui';
 import { Webhook, WebhooksGateway } from '@task-stream/web/tracker/domain';
 import { timeAgo } from './copy';
@@ -38,7 +38,7 @@ const EVENT_LABEL: Record<string, string> = {
 @Component({
   selector: 'ts-webhooks',
   changeDetection: ChangeDetectionStrategy.OnPush,
-  imports: [PiTextFieldComponent],
+  imports: [PiCheckboxComponent, PiTextFieldComponent],
   styleUrl: './settings-card.scss',
   template: `
     <section class="ts-panel ts-block ts-hooks" aria-labelledby="hooks-title">
@@ -113,24 +113,18 @@ const EVENT_LABEL: Record<string, string> = {
         <pi-text-field placeholder="https://…" [(value)]="url" />
         <fieldset class="ts-hooks__picks">
           <legend>Eventos</legend>
-          <label>
-            <input
-              type="checkbox"
-              [checked]="picked().includes('*')"
-              (change)="pick('*', $any($event.target).checked)"
-            />
-            Todos
-          </label>
+          <pi-checkbox
+            label="Todos"
+            [checked]="picked().includes('*')"
+            (checkedChange)="pick('*', $event)"
+          />
           @for (event of events(); track event) {
-            <label>
-              <input
-                type="checkbox"
-                [disabled]="picked().includes('*')"
-                [checked]="picked().includes(event)"
-                (change)="pick(event, $any($event.target).checked)"
-              />
-              {{ label(event) }}
-            </label>
+            <pi-checkbox
+              [label]="label(event)"
+              [disabled]="picked().includes('*')"
+              [checked]="picked().includes(event)"
+              (checkedChange)="pick(event, $event)"
+            />
           }
         </fieldset>
         <div>
@@ -214,11 +208,6 @@ const EVENT_LABEL: Record<string, string> = {
         margin-bottom: 0.25rem;
         color: var(--ts-muted);
       }
-      label {
-        display: flex;
-        gap: 0.375rem;
-        align-items: center;
-      }
     }
   `,
 })