Feature: #109110 - Introduce scheduler task priority 

Description 

A new priority column has been added to the tx_scheduler_task table, allowing administrators to control the execution order of scheduler tasks. Three levels are available:

• High (150)
• Regular (100, default)
• Low (50)

The scheduler now selects the next executable task ordered by priority DESC first, using nextexecution ASC as a secondary tiebreaker. This means a high-priority task that is due will always be executed before a lower-priority task, regardless of how long the lower-priority task has been waiting.

The priority field is exposed as a select field in the Timing tab of the task editing form for all registered task types. The priority of each task is also visible in the scheduler backend module list view.

Extending priority levels 

Extensions can add custom priority levels by extending the TCA of tx_scheduler_task. The priority field is a plain integer column, so any positive integer value is valid. The scheduler module automatically resolves the label for any registered TCA item, so custom values are displayed correctly in the list view. The TCA item's label key must point to a valid language label; if no matching item is found, the raw integer is shown.

\TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addTcaSelectItem(
    'tx_scheduler_task',
    'priority',
    [
        'label' => 'LLL:EXT:my_extension/Resources/Private/Language/locallang.xlf:priority.critical',
        'value' => 200,
    ],
    150,
    'after',
);

Choose integer values that fit naturally into the existing scale (50 / 100 / 150). Values above 150 are executed before High, values below 50 after Low.

Impact 

Administrators can now assign a priority to each scheduler task. Tasks with priority High are picked up before Regular tasks, and Regular before Low tasks. When multiple tasks share the same priority, the longest-overdue task is still selected first, preserving the previous behaviour as a tiebreaker.

Existing tasks receive the default priority Regular (100) automatically via the schema update — no data migration is required.