fix(api): retry commands that clash with a concurrent write

Services run commands through a CommandRunner that runs one again (up to
5 times, waiting a little longer each time) when its aggregate changed
underneath, e.g. a saga writing to the same ticket. Each command loads its
aggregate fresh and stores its events in one transaction, so a
ConcurrencyError means nothing was stored and running it again is safe.
People no longer get a 409 for it, and the e2e suite stops flaking.

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

libs/api/tracker/application/src/lib/comments.service.ts

@@ -1,5 +1,6 @@
+import { CommandRunner } from '@task-stream/api/shared/application';
 import { Injectable } from '@nestjs/common';
-import { CommandBus, QueryBus } from '@nestjs/cqrs';
+import { QueryBus } from '@nestjs/cqrs';
 import { CommentReadModel } from '@task-stream/api/tracker/domain';
 import { AddCommentCommand } from './commands/add-comment.command';
 import { CommandResult } from './commands/command-result';
@@ -12,7 +13,7 @@ import { GetCommentsQuery } from './queries/get-comments.query';
 @Injectable()
 export class CommentsService {
   constructor(
-    private readonly commandBus: CommandBus,
+    private readonly commands: CommandRunner,
     private readonly queryBus: QueryBus,
   ) {}
 
@@ -22,7 +23,7 @@ export class CommentsService {
     body: string,
     replyTo: string | null = null,
   ): Promise<CommandResult> {
-    return this.commandBus.execute(
+    return this.commands.execute(
       new AddCommentCommand(actorId, issueId, body, replyTo),
     );
   }
@@ -32,7 +33,7 @@ export class CommentsService {
     commentId: string,
     body: string,
   ): Promise<CommandResult> {
-    return this.commandBus.execute(
+    return this.commands.execute(
       new EditCommentCommand(actorId, commentId, body),
     );
   }
@@ -44,15 +45,13 @@ export class CommentsService {
     emoji: string,
     on: boolean,
   ): Promise<CommandResult> {
-    return this.commandBus.execute(
+    return this.commands.execute(
       new ReactToCommentCommand(actorId, commentId, emoji, on),
     );
   }
 
   delete(actorId: string, commentId: string): Promise<CommandResult> {
-    return this.commandBus.execute(
-      new DeleteCommentCommand(actorId, commentId),
-    );
+    return this.commands.execute(new DeleteCommentCommand(actorId, commentId));
   }
 
   list(