diff --git a/src/app/issues/[id]/page.tsx b/src/app/issues/[id]/page.tsx
index 171991b..7a57372 100644
--- a/src/app/issues/[id]/page.tsx
+++ b/src/app/issues/[id]/page.tsx
@@ -11,6 +11,7 @@ import { useReference, useReferenceLookups, useWorkflowStates } from "@/lib/stor
 import { useAuth } from "@/lib/auth";
 import { AppShell } from "@/components/layout/AppShell";
 import { ActivityFeed } from "@/components/issues/ActivityFeed";
+import { IssueRelations } from "@/components/issues/IssueRelations";
 import { EmptyState } from "@/components/ui/EmptyState";
 import { TypeIcon } from "@/components/ui/Icons";
 
@@ -74,7 +75,9 @@ function IssueDetail({ issueId }: { issueId: string }) {
         ...partial,
         ...(user ? { actorId: user.id } : {}),
       });
-      setIssue(updated);
+      // Si cambió el padre, el objeto local puede quedar desfasado.
+      const fresh = await api.getIssue(issue.id);
+      setIssue(fresh ?? updated);
       // Refrescar la línea de tiempo con los eventos recién creados.
       void api.listActivity(issue.id).then(setActivity);
     } catch {
@@ -123,6 +126,7 @@ function IssueDetail({ issueId }: { issueId: string }) {
   const project = issue.projectId ? projectById.get(issue.projectId) : undefined;
 
   return (
+    <>
     <div className="detail-grid">
       {/* Columna principal */}
       <div>
@@ -328,5 +332,20 @@ function IssueDetail({ issueId }: { issueId: string }) {
         )}
       </aside>
     </div>
+
+    {/* Jerarquía, vínculos y suscriptores (Fase 3) */}
+    <div className="mt-4">
+      <IssueRelations
+        issue={issue}
+        currentUserId={user?.id ?? null}
+        users={new Map(users.map((u) => [u.id, u]))}
+        onChanged={() => {
+          void api.getIssue(issueId).then((fresh) => {
+            if (fresh) setIssue(fresh);
+          });
+        }}
+      />
+    </div>
+    </>
   );
 }
diff --git a/src/components/issues/IssueRelations.tsx b/src/components/issues/IssueRelations.tsx
new file mode 100644
index 0000000..867303f
--- /dev/null
+++ b/src/components/issues/IssueRelations.tsx
@@ -0,0 +1,354 @@
+"use client";
+
+import Link from "next/link";
+import { useCallback, useEffect, useState } from "react";
+import { api, ApiError } from "@/lib/api";
+import type { ID, Issue, Relation, User } from "@/lib/types";
+import { Avatar } from "@/components/ui/Avatar";
+
+interface IssueRelationsProps {
+  issue: Issue;
+  currentUserId: ID | null;
+  users: Map<ID, User>;
+  /** Refresca el issue (el padre/hijos pueden haber cambiado). */
+  onChanged: () => void;
+}
+
+const KIND_LABEL: Record<string, { outgoing: string; incoming: string }> = {
+  blocked_by: { outgoing: "Bloqueado por", incoming: "Bloquea a" },
+  blocks: { outgoing: "Bloquea a", incoming: "Bloqueado por" },
+  related: { outgoing: "Relacionado con", incoming: "Relacionado con" },
+  duplicates: { outgoing: "Duplicado de", incoming: "Duplicado por" },
+};
+
+/**
+ * Jerarquía, vínculos y suscriptores de un issue (Fase 3).
+ *
+ * Todo pasa por los endpoints dedicados de sam, que validan ciclos,
+ * existencia y actores. Los errores del backend se muestran tal cual.
+ */
+export function IssueRelations({ issue, currentUserId, users, onChanged }: IssueRelationsProps) {
+  const [children, setChildren] = useState<Issue[]>([]);
+  const [parent, setParent] = useState<Issue | null>(null);
+  const [relations, setRelations] = useState<Relation[]>([]);
+  const [relatedIssues, setRelatedIssues] = useState<Map<ID, Issue>>(new Map());
+  const [subscribers, setSubscribers] = useState<ID[]>([]);
+  const [error, setError] = useState<string | null>(null);
+
+  // Formularios.
+  const [identifier, setIdentifier] = useState("");
+  const [kind, setKind] = useState("blocked_by");
+  const [newChildTitle, setNewChildTitle] = useState("");
+
+  const refresh = useCallback(async () => {
+    setError(null);
+    try {
+      const [kids, rels, subs] = await Promise.all([
+        api.listChildren(issue.id),
+        api.listRelations(issue.id),
+        api.listSubscribers(issue.id),
+      ]);
+      setChildren(kids);
+      setRelations(rels);
+      setSubscribers(subs);
+
+      // Resolver los issues vinculados + el padre para mostrar identifiers.
+      const ids = new Set<ID>();
+      for (const r of rels) {
+        ids.add(r.fromIssue === issue.id ? r.toIssue : r.fromIssue);
+      }
+      if (issue.parentId) ids.add(issue.parentId);
+
+      const resolved = new Map<ID, Issue>();
+      await Promise.all(
+        [...ids].map(async (id) => {
+          const found = await api.getIssue(id);
+          if (found) resolved.set(id, found);
+        }),
+      );
+      setRelatedIssues(resolved);
+      setParent(issue.parentId ? (resolved.get(issue.parentId) ?? null) : null);
+    } catch (err) {
+      setError(err instanceof Error ? err.message : "Error cargando relaciones");
+    }
+  }, [issue.id, issue.parentId]);
+
+  useEffect(() => {
+    void refresh();
+  }, [refresh]);
+
+  /** Busca un issue por identifier exacto (ej. "PLAT-42"). */
+  async function resolveIdentifier(raw: string): Promise<Issue> {
+    const idf = raw.trim().toUpperCase();
+    if (!idf) throw new Error("Escribe un identificador (ej. PLAT-42).");
+    const found = await api.listIssues({ query: idf });
+    const exact = found.find((i) => i.identifier.toUpperCase() === idf && i.id !== issue.id);
+    if (!exact) throw new Error(`No existe el issue ${idf}.`);
+    return exact;
+  }
+
+  async function run(action: () => Promise<unknown>, after?: () => void) {
+    setError(null);
+    try {
+      await action();
+      after?.();
+      await refresh();
+      onChanged();
+    } catch (err) {
+      setError(err instanceof ApiError ? err.message : err instanceof Error ? err.message : "Error");
+    }
+  }
+
+  const isSubscribed = currentUserId != null && subscribers.includes(currentUserId);
+
+  return (
+    <div className="row g-3">
+      {error && (
+        <div className="col-12">
+          <div className="alert alert-danger py-2" role="alert">
+            {error}
+          </div>
+        </div>
+      )}
+
+      {/* Jerarquía */}
+      <div className="col-md-4">
+        <div className="lp-card p-3 h-100">
+          <div className="detail-section-title">Jerarquía</div>
+
+          {parent ? (
+            <div className="mb-2" style={{ fontSize: 13 }}>
+              <span style={{ color: "var(--inv-muted)" }}>Sub-issue de </span>
+              <Link href={`/issues/${parent.id}`}>
+                <span className="issue-identifier">{parent.identifier}</span>{" "}
+                {parent.title}
+              </Link>
+              <button
+                type="button"
+                className="btn btn-lp btn-sm ms-2"
+                title="Volver a raíz"
+                onClick={() => void run(() => api.setParent(issue.id, null, currentUserId ?? undefined))}
+              >
+                <i className="bx bx-x" />
+              </button>
+            </div>
+          ) : (
+            <p style={{ fontSize: 13, color: "var(--inv-muted)" }}>Issue raíz.</p>
+          )}
+
+          {children.length > 0 && (
+            <ul className="list-unstyled mb-2">
+              {children.map((child) => (
+                <li key={child.id} className="py-1 d-flex align-items-center gap-2">
+                  <Link
+                    href={`/issues/${child.id}`}
+                    style={{ fontSize: 13 }}
+                    className="text-truncate"
+                  >
+                    <span className="issue-identifier">{child.identifier}</span>{" "}
+                    {child.title}
+                  </Link>
+                  <button
+                    type="button"
+                    className="btn btn-lp btn-sm ms-auto"
+                    title="Sacar de la jerarquía"
+                    onClick={() => void run(() => api.setParent(child.id, null, currentUserId ?? undefined))}
+                  >
+                    <i className="bx bx-x" />
+                  </button>
+                </li>
+              ))}
+            </ul>
+          )}
+
+          <form
+            className="d-flex gap-1 mt-2"
+            onSubmit={(e) => {
+              e.preventDefault();
+              const title = newChildTitle.trim();
+              if (!title) return;
+              setNewChildTitle("");
+              void run(async () => {
+                const created = await api.createIssue({
+                  title,
+                  projectId: issue.projectId,
+                  ...(currentUserId ? { actorId: currentUserId } : {}),
+                });
+                await api.setParent(created.id, issue.id, currentUserId ?? undefined);
+              });
+            }}
+          >
+            <input
+              className="form-control form-control-sm"
+              placeholder="Nuevo sub-issue…"
+              value={newChildTitle}
+              onChange={(e) => setNewChildTitle(e.target.value)}
+            />
+            <button type="submit" className="btn btn-accent btn-sm" title="Crear sub-issue">
+              <i className="bx bx-plus" />
+            </button>
+          </form>
+
+          <form
+            className="d-flex gap-1 mt-2"
+            onSubmit={(e) => {
+              e.preventDefault();
+              const idf = identifier;
+              setIdentifier("");
+              void run(async () => {
+                const target = await resolveIdentifier(idf);
+                await api.setParent(target.id, issue.id, currentUserId ?? undefined);
+              });
+            }}
+          >
+            <input
+              className="form-control form-control-sm"
+              placeholder="Añadir existente (PLAT-42)…"
+              value={identifier}
+              onChange={(e) => setIdentifier(e.target.value)}
+            />
+            <button type="submit" className="btn btn-lp btn-sm" title="Mover como sub-issue">
+              <i className="bx bx-plus" />
+            </button>
+          </form>
+        </div>
+      </div>
+
+      {/* Vínculos */}
+      <div className="col-md-4">
+        <div className="lp-card p-3 h-100">
+          <div className="detail-section-title">Vínculos</div>
+
+          {relations.length === 0 && (
+            <p style={{ fontSize: 13, color: "var(--inv-muted)" }}>Sin vínculos.</p>
+          )}
+
+          <ul className="list-unstyled mb-2">
+            {relations.map((rel) => {
+              const outgoing = rel.fromIssue === issue.id;
+              const otherId = outgoing ? rel.toIssue : rel.fromIssue;
+              const other = relatedIssues.get(otherId);
+              const label = outgoing
+                ? (KIND_LABEL[rel.kind]?.outgoing ?? rel.kind)
+                : (KIND_LABEL[rel.kind]?.incoming ?? rel.kind);
+
+              return (
+                <li key={rel.id} className="py-1 d-flex align-items-center gap-2">
+                  <span style={{ fontSize: 12, color: "var(--inv-muted)" }}>{label}</span>
+                  {other ? (
+                    <Link href={`/issues/${other.id}`} style={{ fontSize: 13 }} className="text-truncate">
+                      <span className="issue-identifier">{other.identifier}</span>{" "}
+                      {other.title}
+                    </Link>
+                  ) : (
+                    <span style={{ fontSize: 13 }}>#{otherId}</span>
+                  )}
+                  <button
+                    type="button"
+                    className="btn btn-lp btn-sm ms-auto"
+                    title="Quitar vínculo"
+                    onClick={() =>
+                      void run(() => api.deleteRelation(rel.id, currentUserId ?? undefined))
+                    }
+                  >
+                    <i className="bx bx-x" />
+                  </button>
+                </li>
+              );
+            })}
+          </ul>
+
+          <RelationForm
+            onAdd={(idf, relKind) =>
+              void run(async () => {
+                const target = await resolveIdentifier(idf);
+                await api.addRelation(issue.id, target.id, relKind, currentUserId ?? undefined);
+              })
+            }
+          />
+        </div>
+      </div>
+
+      {/* Suscriptores */}
+      <div className="col-md-4">
+        <div className="lp-card p-3 h-100">
+          <div className="detail-section-title">Suscriptores</div>
+
+          {subscribers.length === 0 && (
+            <p style={{ fontSize: 13, color: "var(--inv-muted)" }}>
+              Nadie sigue este issue todavía.
+            </p>
+          )}
+
+          <div className="d-flex flex-wrap gap-2 mb-2">
+            {subscribers.map((id) => {
+              const member = users.get(id);
+              return (
+                <span key={id} className="d-inline-flex align-items-center gap-1">
+                  <Avatar user={member} />
+                  <span style={{ fontSize: 12 }}>{member?.name ?? id}</span>
+                </span>
+              );
+            })}
+          </div>
+
+          {currentUserId && (
+            <button
+              type="button"
+              className={`btn btn-sm ${isSubscribed ? "btn-lp" : "btn-accent"}`}
+              onClick={() =>
+                void run(() =>
+                  isSubscribed
+                    ? api.unsubscribe(issue.id, currentUserId, currentUserId)
+                    : api.subscribe(issue.id, currentUserId, currentUserId),
+                )
+              }
+            >
+              <i className={`bx ${isSubscribed ? "bx-bell-off" : "bx-bell"} me-1`} />
+              {isSubscribed ? "Dejar de seguir" : "Seguir"}
+            </button>
+          )}
+        </div>
+      </div>
+    </div>
+  );
+}
+
+function RelationForm({ onAdd }: { onAdd: (identifier: string, kind: string) => void }) {
+  const [idf, setIdf] = useState("");
+  const [relKind, setRelKind] = useState("blocked_by");
+
+  return (
+    <form
+      className="d-flex gap-1 mt-2"
+      onSubmit={(e) => {
+        e.preventDefault();
+        if (!idf.trim()) return;
+        onAdd(idf, relKind);
+        setIdf("");
+      }}
+    >
+      <select
+        className="form-select form-select-sm"
+        style={{ maxWidth: 130 }}
+        value={relKind}
+        onChange={(e) => setRelKind(e.target.value)}
+        title="Tipo de vínculo"
+      >
+        <option value="blocked_by">Bloqueado por</option>
+        <option value="blocks">Bloquea a</option>
+        <option value="related">Relacionado</option>
+        <option value="duplicates">Duplica a</option>
+      </select>
+      <input
+        className="form-control form-control-sm"
+        placeholder="PLAT-42…"
+        value={idf}
+        onChange={(e) => setIdf(e.target.value)}
+      />
+      <button type="submit" className="btn btn-lp btn-sm" title="Añadir vínculo">
+        <i className="bx bx-plus" />
+      </button>
+    </form>
+  );
+}
diff --git a/src/lib/api/client.ts b/src/lib/api/client.ts
index dced9c4..b21f368 100644
--- a/src/lib/api/client.ts
+++ b/src/lib/api/client.ts
@@ -1,6 +1,7 @@
 import type {
   Activity,
   Comment,
+  Relation,
   Cycle,
   ID,
   Issue,
@@ -45,6 +46,20 @@ export interface ProyectosApi {
   // Línea de tiempo (Fase 2 en sam): eventos de creación, cambios y comentarios.
   listActivity(issueId: ID): Promise<Activity[]>;
 
+  // Relaciones (Fase 3 en sam)
+  /** Hijos directos (sub-issues). */
+  listChildren(issueId: ID): Promise<Issue[]>;
+  /** Fija el padre (null = raíz). Valida ciclos en el backend. */
+  setParent(issueId: ID, parentId: ID | null, actorId?: ID): Promise<Issue>;
+  /** Vínculos donde el issue participa (cualquier dirección). */
+  listRelations(issueId: ID): Promise<Relation[]>;
+  addRelation(issueId: ID, toIssue: ID, kind: string, actorId?: ID): Promise<Relation>;
+  deleteRelation(relationId: ID, actorId?: ID): Promise<void>;
+  /** idUsuarios suscritos al issue. */
+  listSubscribers(issueId: ID): Promise<ID[]>;
+  subscribe(issueId: ID, userId: ID, actorId?: ID): Promise<void>;
+  unsubscribe(issueId: ID, userId: ID, actorId?: ID): Promise<void>;
+
   // Comentarios
   listComments(issueId: ID): Promise<Comment[]>;
   /** `authorId` es el idUsuario del usuario en sesión. */
diff --git a/src/lib/api/http.ts b/src/lib/api/http.ts
index 4cc86d3..7777341 100644
--- a/src/lib/api/http.ts
+++ b/src/lib/api/http.ts
@@ -1,6 +1,7 @@
 import type {
   Activity,
   Comment,
+  Relation,
   Cycle,
   ID,
   Issue,
@@ -161,6 +162,43 @@ export const httpApi: ProyectosApi = {
 
   listActivity: (issueId: ID) => request<Activity[]>(`/api/proyectos/issues/${issueId}/activity`),
 
+  listChildren: (issueId: ID) => request<Issue[]>(`/api/proyectos/issues/${issueId}/children`),
+
+  setParent: (issueId: ID, parentId: ID | null, actorId?: ID) =>
+    request<Issue>(`/api/proyectos/issues/${issueId}/parent`, {
+      method: "PUT",
+      body: JSON.stringify(actorId ? { parentId, actorId } : { parentId }),
+    }),
+
+  listRelations: (issueId: ID) => request<Relation[]>(`/api/proyectos/issues/${issueId}/relations`),
+
+  addRelation: (issueId: ID, toIssue: ID, kind: string, actorId?: ID) =>
+    request<Relation>(`/api/proyectos/issues/${issueId}/relations`, {
+      method: "POST",
+      body: JSON.stringify({ toIssue: Number(toIssue), kind, actorId }),
+    }),
+
+  deleteRelation: (relationId: ID, actorId?: ID) => {
+    const qs = actorId ? `?actorId=${encodeURIComponent(actorId)}` : "";
+    return request<void>(`/api/proyectos/relations/${relationId}${qs}`, { method: "DELETE" });
+  },
+
+  listSubscribers: (issueId: ID) => request<ID[]>(`/api/proyectos/issues/${issueId}/subscribers`),
+
+  subscribe: (issueId: ID, userId: ID, actorId?: ID) =>
+    request<void>(`/api/proyectos/issues/${issueId}/subscribers`, {
+      method: "POST",
+      body: JSON.stringify({ userId, actorId }),
+    }),
+
+  unsubscribe: (issueId: ID, userId: ID, actorId?: ID) => {
+    const params = new URLSearchParams({ userId });
+    if (actorId) params.append("actorId", actorId);
+    return request<void>(`/api/proyectos/issues/${issueId}/subscribers?${params}`, {
+      method: "DELETE",
+    });
+  },
+
   listComments: (issueId: ID) => request<Comment[]>(`/api/proyectos/issues/${issueId}/comments`),
 
   addComment: (issueId: ID, body: string, authorId: ID) =>
diff --git a/src/lib/api/mock.ts b/src/lib/api/mock.ts
index 44091eb..0fc9e29 100644
--- a/src/lib/api/mock.ts
+++ b/src/lib/api/mock.ts
@@ -1,6 +1,7 @@
 import type {
   Activity,
   Comment,
+  Relation,
   Cycle,
   ID,
   Issue,
@@ -27,6 +28,8 @@ const state = {
   issues: structuredClone(seed.issues),
   comments: structuredClone(seed.comments),
   activity: [] as Activity[],
+  relations: [] as Relation[],
+  subscriptions: [] as Array<{ issueId: ID; userId: ID }>,
   projects: structuredClone(seed.projects),
   cycles: structuredClone(seed.cycles),
   users: structuredClone(seed.users),
@@ -212,6 +215,7 @@ export const mockApi: ProyectosApi = {
       title: input.title,
       description: input.description ?? "",
       status,
+      parentId: null,
       priority: input.priority ?? 0,
       type: input.type ?? "task",
       assigneeId: input.assigneeId ?? null,
@@ -250,6 +254,7 @@ export const mockApi: ProyectosApi = {
     if (patch.assigneeId !== undefined) track("assignee", issue.assigneeId, patch.assigneeId);
     if (patch.projectId !== undefined) track("project", issue.projectId, patch.projectId);
     if (patch.cycleId !== undefined) track("cycle", issue.cycleId, patch.cycleId);
+    if (patch.parentId !== undefined) track("parent", issue.parentId ?? null, patch.parentId);
     if (patch.labelIds !== undefined)
       track("labels", issue.labelIds.join(","), patch.labelIds.join(","));
 
@@ -264,6 +269,87 @@ export const mockApi: ProyectosApi = {
     return issue;
   },
 
+  async listChildren(issueId: ID): Promise<Issue[]> {
+    await delay(60);
+    return state.issues.filter((i) => (i.parentId ?? null) === issueId);
+  },
+
+  async setParent(issueId: ID, parentId: ID | null, actorId?: ID): Promise<Issue> {
+    await delay(120);
+    const issue = state.issues.find((i) => i.id === issueId);
+    if (!issue) throw new Error(`Issue ${issueId} no encontrado`);
+    if (parentId !== null) {
+      if (parentId === issueId) throw new Error("Un issue no puede ser su propio padre.");
+      if (!state.issues.some((i) => i.id === parentId)) throw new Error("Padre inexistente.");
+      // Caminata de ancestros (réplica simplificada del backend).
+      let ancestor: ID | null | undefined = parentId;
+      while (ancestor != null) {
+        if (ancestor === issueId) throw new Error("Asignar ese padre crearía un ciclo en la jerarquía.");
+        ancestor = state.issues.find((i) => i.id === ancestor)?.parentId;
+      }
+    }
+    const old = issue.parentId ?? null;
+    issue.parentId = parentId;
+    issue.updatedAt = new Date().toISOString();
+    if (old !== parentId) logActivity(issueId, actorId ?? null, "parent", old, parentId);
+    return issue;
+  },
+
+  async listRelations(issueId: ID): Promise<Relation[]> {
+    await delay(60);
+    return state.relations.filter((r) => r.fromIssue === issueId || r.toIssue === issueId);
+  },
+
+  async addRelation(issueId: ID, toIssue: ID, kind: string, actorId?: ID): Promise<Relation> {
+    await delay(120);
+    if (issueId === toIssue) throw new Error("Un issue no puede vincularse consigo mismo.");
+    if (!state.issues.some((i) => i.id === issueId && i)) throw new Error("Issue inexistente.");
+    if (!state.issues.some((i) => i.id === toIssue)) throw new Error("Issue destino inexistente.");
+    const existing = state.relations.find(
+      (r) => r.fromIssue === issueId && r.toIssue === toIssue && r.kind === kind,
+    );
+    if (existing) return existing;
+    const rel: Relation = {
+      id: nextId("rel"),
+      fromIssue: issueId,
+      toIssue,
+      kind,
+      createdAt: new Date().toISOString(),
+    };
+    state.relations.push(rel);
+    logActivity(issueId, actorId ?? null, "relation_added", null, `${kind}:${toIssue}`);
+    return rel;
+  },
+
+  async deleteRelation(relationId: ID, actorId?: ID): Promise<void> {
+    await delay(100);
+    const rel = state.relations.find((r) => r.id === relationId);
+    if (!rel) return;
+    state.relations = state.relations.filter((r) => r.id !== relationId);
+    logActivity(rel.fromIssue, actorId ?? null, "relation_removed", `${rel.kind}:${rel.toIssue}`, null);
+  },
+
+  async listSubscribers(issueId: ID): Promise<ID[]> {
+    await delay(60);
+    return state.subscriptions.filter((s) => s.issueId === issueId).map((s) => s.userId);
+  },
+
+  async subscribe(issueId: ID, userId: ID, actorId?: ID): Promise<void> {
+    await delay(100);
+    if (!state.subscriptions.some((s) => s.issueId === issueId && s.userId === userId)) {
+      state.subscriptions.push({ issueId, userId });
+      logActivity(issueId, actorId ?? userId, "subscribed", null, userId);
+    }
+  },
+
+  async unsubscribe(issueId: ID, userId: ID, actorId?: ID): Promise<void> {
+    await delay(100);
+    state.subscriptions = state.subscriptions.filter(
+      (s) => !(s.issueId === issueId && s.userId === userId),
+    );
+    logActivity(issueId, actorId ?? userId, "unsubscribed", userId, null);
+  },
+
   async listActivity(issueId: ID): Promise<Activity[]> {
     await delay(60);
     return state.activity
diff --git a/src/lib/seed.ts b/src/lib/seed.ts
index 8310858..b8bb3e9 100644
--- a/src/lib/seed.ts
+++ b/src/lib/seed.ts
@@ -113,6 +113,7 @@ export const issues: Issue[] = [
     assigneeId: "u1",
     projectId: "p1",
     cycleId: "c3",
+    parentId: null,
     labelIds: ["l2"],
     createdAt: "2026-10-01T09:15:00Z",
     updatedAt: "2026-10-12T15:40:00Z",
@@ -129,6 +130,7 @@ export const issues: Issue[] = [
     assigneeId: "u2",
     projectId: "p1",
     cycleId: "c3",
+    parentId: null,
     labelIds: ["l1", "l4"],
     createdAt: "2026-10-03T11:00:00Z",
     updatedAt: "2026-10-10T08:20:00Z",
@@ -145,6 +147,7 @@ export const issues: Issue[] = [
     assigneeId: "u4",
     projectId: "p1",
     cycleId: "c3",
+    parentId: null,
     labelIds: ["l3"],
     createdAt: "2026-09-28T14:30:00Z",
     updatedAt: "2026-10-11T17:05:00Z",
@@ -161,6 +164,7 @@ export const issues: Issue[] = [
     assigneeId: "u3",
     projectId: "p1",
     cycleId: "c3",
+    parentId: null,
     labelIds: ["l2"],
     createdAt: "2026-09-20T10:00:00Z",
     updatedAt: "2026-10-08T12:00:00Z",
@@ -177,6 +181,7 @@ export const issues: Issue[] = [
     assigneeId: null,
     projectId: "p2",
     cycleId: null,
+    parentId: null,
     labelIds: ["l1", "l3"],
     createdAt: "2026-10-06T09:00:00Z",
     updatedAt: "2026-10-06T09:00:00Z",
@@ -193,6 +198,7 @@ export const issues: Issue[] = [
     assigneeId: "u1",
     projectId: "p2",
     cycleId: "c4",
+    parentId: "i5",
     labelIds: ["l2"],
     createdAt: "2026-10-07T16:45:00Z",
     updatedAt: "2026-10-09T10:10:00Z",
@@ -209,6 +215,7 @@ export const issues: Issue[] = [
     assigneeId: "u3",
     projectId: "p3",
     cycleId: "c2",
+    parentId: null,
     labelIds: ["l5"],
     createdAt: "2026-08-15T13:20:00Z",
     updatedAt: "2026-09-30T09:00:00Z",
@@ -225,6 +232,7 @@ export const issues: Issue[] = [
     assigneeId: "u2",
     projectId: "p1",
     cycleId: "c4",
+    parentId: null,
     labelIds: ["l5"],
     createdAt: "2026-10-09T08:00:00Z",
     updatedAt: "2026-10-09T08:00:00Z",
diff --git a/src/lib/types.ts b/src/lib/types.ts
index f1c327b..1ec5b7e 100644
--- a/src/lib/types.ts
+++ b/src/lib/types.ts
@@ -118,6 +118,8 @@ export interface Issue {
   assigneeId: ID | null;
   projectId: ID | null;
   cycleId: ID | null;
+  /** Id del issue padre (sub-issues, Fase 3 en sam). Null/ausente = raíz. */
+  parentId: ID | null;
   labelIds: ID[];
   createdAt: string;
   updatedAt: string;
@@ -149,6 +151,19 @@ export interface IssueInput {
   assigneeId?: ID | null;
   projectId?: ID | null;
   cycleId?: ID | null;
+  parentId?: ID | null;
   labelIds?: ID[];
   actorId?: ID;
 }
+
+/**
+ * Vínculo tipado entre issues (Fase 3 en sam).
+ * kind: blocked_by, blocks, related, duplicates.
+ */
+export interface Relation {
+  id: ID;
+  fromIssue: ID;
+  toIssue: ID;
+  kind: string;
+  createdAt: string;
+}