feat: an ordered backlog

A Backlog tab lists the tickets still to start in the order the team will
take them; drag them, or use the arrows, to reorder. Moving a ticket only
rewrites that ticket's rank, read from the event store, and board columns
follow the same order.

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

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

@@ -9,6 +9,7 @@ import {
   FindReleasesRepository,
   FindTimelineRepository,
   IssueFilter,
+  IssueSort,
   Page,
 } from '@task-stream/api/tracker/application';
 import {
@@ -135,7 +136,11 @@ export class MongoFindIssuesRepository extends FindIssuesRepository {
     const [docs, total] = await Promise.all([
       this.issues
         .find(query)
-        .sort({ updatedAt: -1 })
+        .sort(
+          filter.sort === IssueSort.RANK
+            ? { rank: 1, number: 1 }
+            : { updatedAt: -1 },
+        )
         .skip(filter.offset)
         .limit(filter.limit)
         .lean<IssueDoc[]>(),

libs/api/tracker/infrastructure/src/lib/mongo/rank.backfill.ts

@@ -0,0 +1,36 @@
+import { Injectable, Logger, OnApplicationBootstrap } from '@nestjs/common';
+import { InjectModel } from '@nestjs/mongoose';
+import { implicitRank } from '@task-stream/api/tracker/domain';
+import { Model } from 'mongoose';
+import { IssueDoc, ReadModels } from './read-model.schemas';
+
+/**
+ * Tickets projected before the backlog could be ordered lack `rank`; give
+ * them their creation order once at startup, the rank they have anyway.
+ */
+@Injectable()
+export class RankBackfill implements OnApplicationBootstrap {
+  private readonly logger = new Logger(RankBackfill.name);
+
+  constructor(
+    @InjectModel(ReadModels.Issue) private readonly issues: Model<IssueDoc>,
+  ) {}
+
+  async onApplicationBootstrap(): Promise<void> {
+    const missing = await this.issues
+      .find({ rank: { $exists: false } }, { 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 } },
+          update: { $set: { rank: implicitRank(doc.number) } },
+        },
+      })),
+    );
+    this.logger.log(
+      `Backlog rank filled in on ${result.modifiedCount} tickets`,
+    );
+  }
+}

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

@@ -7,6 +7,7 @@ import {
   IssueTimelineEntry,
   ProjectReadModel,
   ReleaseReadModel,
+  implicitRank,
 } from '@task-stream/api/tracker/domain';
 import { Schema } from 'mongoose';
 
@@ -102,6 +103,7 @@ IssueSchema.index({ projectId: 1, statusCategory: 1 });
 IssueSchema.index({ 'assignee.id': 1 });
 IssueSchema.index({ 'watchers.id': 1 });
 IssueSchema.index({ 'parent.id': 1 });
+IssueSchema.index({ projectId: 1, rank: 1 });
 IssueSchema.index({ 'release.id': 1 });
 IssueSchema.index({ title: 'text', description: 'text', key: 'text' });
 
@@ -186,6 +188,7 @@ export function issueFromDoc(doc: IssueDoc): IssueReadModel {
     attachments: rest.attachments ?? [],
     watchers: rest.watchers ?? [],
     parent: rest.parent?.id ? rest.parent : null,
+    rank: rest.rank ?? implicitRank(rest.number),
     checklist: rest.checklist ?? [],
   };
 }