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

@@ -4,6 +4,7 @@ import {
   Delete,
   Get,
   Param,
+  ParseUUIDPipe,
   Patch,
   Post,
   Put,
@@ -35,6 +36,7 @@ import { withoutNulls } from '../common/issue-input';
 import {
   AssignIssueDto,
   ChangeStatusDto,
+  ChecklistItemBodyDto,
   CommentBodyDto,
   CreateIssueDto,
   IssueSearchQueryDto,
@@ -42,13 +44,16 @@ import {
   LinkTypeParamDto,
   MyIssuesQueryDto,
   PageQueryDto,
+  SetIssueParentDto,
   SetIssueReleaseDto,
+  UpdateChecklistItemDto,
   UpdateIssueDto,
 } from './dto/requests.dto';
 import {
   ActivityDto,
   CommandResultDto,
   CommentPageDto,
+  EpicDto,
   IssueDto,
   IssuePageDto,
 } from './dto/responses.dto';
@@ -139,6 +144,9 @@ export class IssuesController {
   ) {
     const page = await this.issues.search(viewerOf(me), {
       projectId: await this.refs.projectId(viewerOf(me), project),
+      parentId: query.parent
+        ? await this.refs.issueId(viewerOf(me), query.parent)
+        : undefined,
       statuses: query.status,
       categories: query.category,
       types: query.type,
@@ -169,12 +177,40 @@ export class IssuesController {
     @Param('project') project: string,
     @Body() body: CreateIssueDto,
   ) {
+    const { parent, ...fields } = body;
     return this.issues.create(me.id, {
-      ...withoutNulls(body),
+      ...withoutNulls(fields),
       projectId: await this.refs.projectId(me.id, project),
+      parentId: parent ? await this.refs.issueId(me.id, parent) : null,
     });
   }
 
+  @Get('projects/:project/epics')
+  @ApiOptionalPireonAuth()
+  @PROJECT
+  @ApiOperation({
+    summary: 'Epics: top-level tickets that group others',
+    description:
+      'With the progress of the tickets hanging from each one (done or cancelled, and story points).',
+  })
+  @ApiOkResponse({ type: [EpicDto] })
+  @ApiReadErrors()
+  async epics(
+    @CurrentUser() me: User | undefined,
+    @Param('project') project: string,
+  ) {
+    const epics = await this.issues.epics(
+      viewerOf(me),
+      await this.refs.projectId(viewerOf(me), project),
+    );
+    return Promise.all(
+      epics.map(async (epic) => ({
+        ...epic,
+        issue: await this.refs.issueDto(epic.issue),
+      })),
+    );
+  }
+
   @Get('issues/:issue')
   @ApiOptionalPireonAuth()
   @ISSUE
@@ -266,6 +302,82 @@ export class IssuesController {
     );
   }
 
+  @Put('issues/:issue/parent')
+  @ISSUE
+  @ApiOperation({
+    summary: 'Place the ticket under an epic or another ticket',
+    description:
+      'Same project, three levels at most (epic → ticket → subtask), no loops. null takes it back to the top.',
+  })
+  @ApiOkResponse({ type: CommandResultDto })
+  @ApiCommandErrors()
+  async setParent(
+    @CurrentUser() me: User,
+    @Param('issue') issue: string,
+    @Body() body: SetIssueParentDto,
+  ) {
+    return this.issues.setParent(
+      me.id,
+      await this.refs.issueId(me.id, issue),
+      body.parent ? await this.refs.issueId(me.id, body.parent) : null,
+    );
+  }
+
+  @Post('issues/:issue/checklist')
+  @ISSUE
+  @ApiOperation({ summary: "Add a step to the ticket's checklist" })
+  @ApiCreatedResponse({ type: CommandResultDto })
+  @ApiCommandErrors()
+  async addChecklistItem(
+    @CurrentUser() me: User,
+    @Param('issue') issue: string,
+    @Body() body: ChecklistItemBodyDto,
+  ) {
+    return this.issues.addChecklistItem(
+      me.id,
+      await this.refs.issueId(me.id, issue),
+      body.text,
+    );
+  }
+
+  @Patch('issues/:issue/checklist/:item')
+  @ISSUE
+  @ApiParam({ name: 'item', format: 'uuid' })
+  @ApiOperation({ summary: 'Reword, tick or untick a checklist step' })
+  @ApiOkResponse({ type: CommandResultDto })
+  @ApiCommandErrors()
+  async updateChecklistItem(
+    @CurrentUser() me: User,
+    @Param('issue') issue: string,
+    @Param('item', ParseUUIDPipe) item: string,
+    @Body() body: UpdateChecklistItemDto,
+  ) {
+    return this.issues.updateChecklistItem(
+      me.id,
+      await this.refs.issueId(me.id, issue),
+      item,
+      body,
+    );
+  }
+
+  @Delete('issues/:issue/checklist/:item')
+  @ISSUE
+  @ApiParam({ name: 'item', format: 'uuid' })
+  @ApiOperation({ summary: 'Remove a checklist step' })
+  @ApiOkResponse({ type: CommandResultDto })
+  @ApiCommandErrors()
+  async removeChecklistItem(
+    @CurrentUser() me: User,
+    @Param('issue') issue: string,
+    @Param('item', ParseUUIDPipe) item: string,
+  ) {
+    return this.issues.removeChecklistItem(
+      me.id,
+      await this.refs.issueId(me.id, issue),
+      item,
+    );
+  }
+
   @Post('issues/:issue/links')
   @ISSUE
   @ApiOperation({