Migration: Re-use async batch infrastructure

[obenland]

Proposed changes:

• Replace hardcoded allowlist in Scheduler with extensible registration system
• Add Scheduler::register_async_batch_callback() method for dynamic callback registration
• Remove hardcoded Migration callbacks from Scheduler class
• Update Migration class to register its callbacks through new registration system
• Add safety check to ensure callbacks are registered at proper time
• Maintain full backward compatibility - async_batch works exactly the same way

Other information:

• Have you written new tests for your changes, if applicable?

Testing instructions:

• Run the existing test suite to verify backward compatibility:

  npm run env-test -- --filter Test_Scheduler

• All 12 tests should pass, confirming async batch functionality works as before
• Test that Migration callbacks are properly registered and functional:

  npm run env-test -- --filter test_update_comment_counts_with_existing_valid_lock
  npm run env-test -- --filter test_async_upgrade

Usage for other plugins/classes:

Any class can now register async batch jobs without modifying core files:

class My_Custom_Jobs {
    public static function init() {
        // Must be called before or during 'init' action
        Scheduler::register_async_batch_callback( 'my_custom_hook', array( self::class, 'my_batch_method' ) );
    }
    
    public static function my_batch_method( $batch_size = 50, $offset = 0 ) {
        // Your batch processing logic
        // Return array for next batch or null when done
    }
}

Changelog entry

• Automatically create a changelog entry from the details below.

Changelog Entry Details

Significance

• Patch
• Minor
• Major

Type

• Added - for new features
• Changed - for changes in existing functionality
• Deprecated - for soon-to-be removed features
• Removed - for now removed features
• Fixed - for any bug fixes
• Security - in case of vulnerabilities

Message

Add extensible async batch callback registration system to replace hardcoded allowlist

[pfefferle]

@obenland what about this PR?

[obenland]

Depends on #1521.

[obenland]

@pfefferle This should be ready for review

[obenland]

After team call: Let's make it possible to fill the Scheduler from class-migrations.php.

Meaning, how can we expand the batch callback allow list from the migration class.
Also move action hooks back into the migration class.
Could also be done in Migration::async_migration.

[Copilot]

Pull Request Overview

This PR refactors migration jobs to reuse the existing Scheduler::async_batch infrastructure instead of having their own dedicated scheduling system. The changes consolidate job scheduling through a unified batch processing system.

Key changes:

• Removes custom migration scheduling methods and replaces them with async_batch infrastructure
• Updates test coverage to reflect the new scheduling approach
• Simplifies the migration job architecture by eliminating duplicate scheduling logic

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
includes/class-migration.php	Removes async_migration and async_upgrade methods, updates migration scheduling to use async_batch
includes/class-scheduler.php	Adds migration callbacks to batch_callbacks array and registers corresponding action hooks
tests/includes/class-test-migration.php	Updates tests to use new Scheduler::async_batch approach and removes old migration-specific tests
tests/includes/class-test-scheduler.php	Adds new tests for migration functionality using the async_batch infrastructure

Comments suppressed due to low confidence (1)

tests/includes/class-test-migration.php:1

• Inconsistent factory usage. Line 381 uses self::factory()->post->create() while line 481 uses $this->factory->post->create(). Should use the same pattern throughout the file.

<?php

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