Throttled campaign batch sender

<?php

namespace App\Actions;

use App\Jobs\SendChunk;
use App\Models\Campaign;
use Illuminate\Bus\Batch;
use Illuminate\Support\Facades\Bus;

class SendCampaign
{
    public function __invoke(Campaign $campaign, int $chunkSize = 200): Batch
    {
        $jobs = [];

        // chunkById keeps memory flat even for very large audiences.
        $campaign->recipients()->select('id')->chunkById($chunkSize, function ($rows) use (&$jobs, $campaign) {
            $jobs[] = new SendChunk($campaign->id, $rows->first()->id, $rows->last()->id);
        });

        return Bus::batch($jobs)
            ->name("campaign-{$campaign->id}")
            ->allowFailures()
            ->finally(fn () => $campaign->update(['status' => 'sent', 'finished_at' => now()]))
            ->onQueue('mail')
            ->dispatch();
    }
}

<?php

namespace App\Jobs;

use App\Mail\CampaignMail;
use App\Models\Campaign;
use App\Models\CampaignRecipient;
use Illuminate\Bus\Batchable;
use Illuminate\Contracts\Queue\ShouldQueue;
use Illuminate\Foundation\Queue\Queueable;
use Illuminate\Support\Facades\Mail;
use Illuminate\Support\Facades\RateLimiter;

class SendChunk implements ShouldQueue
{
    use Batchable, Queueable;

    public int $tries = 0;      // rate-limit releases must not count as failures
    public int $maxExceptions = 3;

    public function __construct(private int $campaignId, private int $fromId, private int $toId) {}

    public function handle(): void
    {
        if ($this->batch()?->cancelled()) {
            return;
        }

        $campaign = Campaign::findOrFail($this->campaignId);
        $cap = (int) config('mail.cap_per_minute', 300);

        CampaignRecipient::where('campaign_id', $campaign->id)
            ->whereBetween('id', [$this->fromId, $this->toId])
            ->whereNull('sent_at')
            ->with('contact')
            ->each(function (CampaignRecipient $recipient) use ($campaign, $cap) {
                // No budget left this minute: put the job back and try later.
                if (! RateLimiter::attempt('send:mail', $cap, fn () => true, 60)) {
                    $this->release(RateLimiter::availableIn('send:mail'));

                    return false;
                }

                // Claim first, so a retried chunk never mails the same person twice.
                if (CampaignRecipient::whereKey($recipient->id)->whereNull('sent_at')->update(['sent_at' => now()])) {
                    Mail::to($recipient->contact->address)->send(new CampaignMail($campaign, $recipient));
                }
            });
    }
}