feat: epics, subtasks and checklists

Tickets can hang from another one of the same project, three levels deep
at most (epic → ticket → subtask). The ticket page lists its subtasks with
their progress, creates new ones and moves the ticket under an epic; a new
Épicas tab shows every epic and how far it has got. Each ticket also gets a
checklist for the small steps that don't deserve a ticket.

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

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

@@ -0,0 +1,28 @@
+import { StatusCategory } from './enums';
+import { checklistProgress, childProgress } from './hierarchy';
+import { IssueSummary } from './models';
+
+const child = (statusCategory: StatusCategory) =>
+  ({ statusCategory }) as IssueSummary;
+
+describe('hierarchy', () => {
+  it('counts done and cancelled subtasks as finished', () => {
+    expect(
+      childProgress([
+        child(StatusCategory.DONE),
+        child(StatusCategory.CANCELLED),
+        child(StatusCategory.IN_PROGRESS),
+      ]),
+    ).toMatchObject({ total: 3, finished: 2, percent: 67 });
+    expect(childProgress([]).percent).toBe(0);
+  });
+
+  it('counts ticked checklist steps', () => {
+    expect(
+      checklistProgress([
+        { id: 'a', text: 'a', done: true },
+        { id: 'b', text: 'b', done: false },
+      ]),
+    ).toEqual({ done: 1, total: 2 });
+  });
+});

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

@@ -0,0 +1,32 @@
+import { ChecklistItem, ChildProgress, IssueSummary } from './models';
+import { StatusCategory } from './enums';
+
+const FINISHED: StatusCategory[] = [
+  StatusCategory.DONE,
+  StatusCategory.CANCELLED,
+];
+
+/** Progress of the tickets hanging from one (story points are not loaded here). */
+export function childProgress(children: IssueSummary[]): ChildProgress {
+  const finished = children.filter((c) =>
+    FINISHED.includes(c.statusCategory),
+  ).length;
+  return {
+    total: children.length,
+    finished,
+    percent:
+      children.length === 0
+        ? 0
+        : Math.round((finished / children.length) * 100),
+    storyPoints: 0,
+    finishedStoryPoints: 0,
+  };
+}
+
+/** "3/5": ticked steps of a checklist. */
+export function checklistProgress(items: ChecklistItem[]): {
+  done: number;
+  total: number;
+} {
+  return { done: items.filter((i) => i.done).length, total: items.length };
+}

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

@@ -30,10 +30,12 @@ export interface CreateIssueInput {
   figmaUrl?: string | null;
   assigneeId?: string | null;
   releaseId?: string | null;
+  /** Epic or ticket the new one breaks down. */
+  parentId?: string | null;
 }
 
 export type UpdateIssueInput = Partial<
-  Omit<CreateIssueInput, 'projectId' | 'assigneeId' | 'releaseId'>
+  Omit<CreateIssueInput, 'projectId' | 'assigneeId' | 'releaseId' | 'parentId'>
 > & {
   issueId: string;
 };

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

@@ -40,6 +40,36 @@ export interface IssueLink {
   issueKey: string;
 }
 
+/** The ticket another one hangs from. */
+export interface IssueParent {
+  id: string;
+  key: string;
+  title: string;
+}
+
+/** A step inside a ticket that does not deserve a ticket of its own. */
+export interface ChecklistItem {
+  id: string;
+  text: string;
+  done: boolean;
+}
+
+/** How far the tickets hanging from one have got. */
+export interface ChildProgress {
+  total: number;
+  /** Done or cancelled. */
+  finished: number;
+  percent: number;
+  storyPoints: number;
+  finishedStoryPoints: number;
+}
+
+/** A top-level ticket that groups others. */
+export interface Epic {
+  issue: IssueSummary;
+  progress: ChildProgress;
+}
+
 /** What boards and lists show. */
 export interface IssueSummary {
   id: string;
@@ -55,6 +85,8 @@ export interface IssueSummary {
   assignee: UserRef | null;
   release: { id: string; name: string } | null;
   labels: string[];
+  /** The epic or ticket this one breaks down. */
+  parent: IssueParent | null;
   commentCount: number;
   updatedAt: string;
   version: number;
@@ -88,6 +120,7 @@ export interface Issue extends IssueSummary {
   attachments: Attachment[];
   /** People following the ticket. */
   watchers: UserRef[];
+  checklist: ChecklistItem[];
   allowedTransitions: string[];
   createdAt: string;
 }

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

@@ -4,6 +4,7 @@ import {
   Attachment,
   BoardColumn,
   Comment,
+  Epic,
   CommandResult,
   Issue,
   IssuePage,
@@ -89,6 +90,30 @@ export abstract class IssuesGateway {
   ): Observable<CommandResult>;
   /** The signed-in person follows (or stops following) the ticket. */
   abstract watch(issueId: string, watching: boolean): Observable<CommandResult>;
+  /** Tickets hanging from `issueId`. */
+  abstract children(
+    projectId: string,
+    issueId: string,
+  ): Observable<IssueSummary[]>;
+  /** Places the ticket under `parentId` (null: back to the top). */
+  abstract setParent(
+    issueId: string,
+    parentId: string | null,
+  ): Observable<CommandResult>;
+  abstract epics(projectId: string): Observable<Epic[]>;
+  abstract addChecklistItem(
+    issueId: string,
+    text: string,
+  ): Observable<CommandResult>;
+  abstract updateChecklistItem(
+    issueId: string,
+    itemId: string,
+    changes: { text?: string; done?: boolean },
+  ): Observable<CommandResult>;
+  abstract removeChecklistItem(
+    issueId: string,
+    itemId: string,
+  ): Observable<CommandResult>;
 }
 
 export abstract class CommentsGateway {