Ensure campaign recipients are deduped across multiple lists

[Copilot]

Campaigns targeting multiple lists could queue duplicate emails for subscribers present in more than one list. One-time sends remain unaffected.

• Deduplication before queueing: Added subscriber de-duplication (by email and ID) in Email_Service::queue_campaign to guarantee each recipient is queued once even if they appear in multiple lists.
• Test coverage: Added a unit test confirming duplicates across lists are removed before queue generation.

Example:

$campaign_id = $email_service->queue_campaign( array(
    'subject'     => 'Update',
    'body'        => '<p>Hello</p>',
    'list_ids'    => array( 1, 2 ),
    'subscribers' => array(
        (object) array( 'id' => 10, 'email' => 'dup@example.com' ),
        (object) array( 'id' => 11, 'email' => 'unique@example.com' ),
        (object) array( 'id' => 10, 'email' => 'dup@example.com' ), // deduped
    ),
) );
// Only two queue entries are created despite the duplicate

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• https://api.github.com/repos/Brain-WP/BrainMonkey/zipball/d95a9d895352c30f47604ad1b825ab8fa9d1a373
  • Triggering command: /usr/bin/php8.3 /usr/bin/php8.3 -n -c /tmp/ORxdiz /usr/bin/composer install (http block)
• https://api.github.com/repos/PHPCSStandards/PHP_CodeSniffer/zipball/0ca86845ce43291e8f5692c7356fccf3bcf02bf4
  • Triggering command: /usr/bin/php8.3 /usr/bin/php8.3 -n -c /tmp/ORxdiz /usr/bin/composer install (http block)
• https://api.github.com/repos/PHPCSStandards/composer-installer/zipball/845eb62303d2ca9b289ef216356568ccc075ffd1
  • Triggering command: /usr/bin/php8.3 /usr/bin/php8.3 -n -c /tmp/ORxdiz /usr/bin/composer install (http block)
• https://api.github.com/repos/antecedent/patchwork/zipball/8b6b235f405af175259c8f56aea5fc23ab9f03ce
  • Triggering command: /usr/bin/php8.3 /usr/bin/php8.3 -n -c /tmp/ORxdiz /usr/bin/composer install (http block)
• https://api.github.com/repos/composer/installers/zipball/12fb2dfe5e16183de69e784a7b84046c43d97e8e
  • Triggering command: /usr/bin/php8.3 /usr/bin/php8.3 -n -c /tmp/ORxdiz /usr/bin/composer install (http block)
• https://api.github.com/repos/doctrine/instantiator/zipball/c6222283fa3f4ac679f8b9ced9a4e23f163e80d0
  • Triggering command: /usr/bin/php8.3 /usr/bin/php8.3 -n -c /tmp/ORxdiz /usr/bin/composer install (http block)
• https://api.github.com/repos/hamcrest/hamcrest-php/zipball/f8b1c0173b22fa6ec77a81fe63e5b01eba7e6487
  • Triggering command: /usr/bin/php8.3 /usr/bin/php8.3 -n -c /tmp/ORxdiz /usr/bin/composer install (http block)
• https://api.github.com/repos/mockery/mockery/zipball/1f4efdd7d3beafe9807b08156dfcb176d18f1699
  • Triggering command: /usr/bin/php8.3 /usr/bin/php8.3 -n -c /tmp/ORxdiz /usr/bin/composer install (http block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Multiple lists in a campaign</issue_title>
<issue_description>What happens when multiple lists are selected in a campaign? If a subscriber is in two lists, he should get the email only once even if the campaign is targeting multiple lists.</issue_description>

<agent_instructions>Analyze campaign and one-time email sending behavior</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Multiple lists in a campaign #85

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