fix: delete expired presence rows by key in bounded passes

[aldorizona10-glitch]

What & why

Resolves #206. wp_delete_expired_presence_data() (includes/functions.php) batched deletions with a MySQL-only DELETE ... LIMIT inside a loop that had no iteration ceiling:

do {
	$deleted = $wpdb->query(
		$wpdb->prepare( "DELETE FROM {$wpdb->presence} WHERE date_gmt < %s LIMIT 1000", $cutoff )
	);
} while ( $deleted > 0 );

Two divergences from core, both from #206:

1. Portability — DELETE ... LIMIT is MySQL-specific and appears nowhere in wp-includes, so it breaks on non-MySQL backends, including the SQLite integration Playground uses to run the demo blueprints.
2. Unbounded work — a site returning from a cron outage with a large backlog keeps looping until max_execution_time, committing an unpredictable fraction of the work.

Change

Follows core's batching convention — select a bounded set of primary keys, delete by key, a fixed number of passes per invocation, remainder to the next run:

• Each pass SELECTs a page of ids older than the cutoff (LIMIT %d) and deletes them with a portable WHERE id IN ( ... ) built from %d placeholders passed through prepare().
• A fixed max passes per invocation bounds the work; the cron event fires every minute, so any remaining backlog drains over subsequent runs instead of in one long request.
• Batch size (default 1000) and passes per run (default 10) are filterable via wp_presence_cleanup_batch_size and wp_presence_cleanup_max_passes.

No schema change; behavior on a normally-drained table is unchanged.

Tests

Added to tests/test-functions.php (@covers ::wp_delete_expired_presence_data):

• test_cleanup_is_bounded_per_invocation — with batch_size and max_passes filtered to 2, seeds 5 expired rows and asserts one invocation deletes at most 2 × 2 = 4, leaving the remainder; a second invocation clears it. This locks in the "remainder to the next run" guarantee.
• test_cleanup_leaves_fresh_entries_untouched — fresh rows survive cleanup even with a batch size of one.

The existing test_cleanup_removes_expired_entries continues to pass.

Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code
Model(s): Claude Opus 4.8
Used for: Investigating core's batching convention, implementing the fix, and writing tests

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

Core Committers: Use this line as a base for the props when committing in SVN:

Props aldorza, joefusco.

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

[github-actions]

▶ Preview in WordPress Playground

Boots a fresh WordPress with this PR's presence-api build, seeds 5 demo users, and drops you on the dashboard.

_{Stress-test variant: 40 demo users · Built from 30a8cfa3048d107ee09a09084398869a36930a56. Auto-updates when you push.}

[codecov]

Codecov Report

❌ Patch coverage is 93.75000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 72.63%. Comparing base (bfb701f) to head (30a8cfa).

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #258      +/-   ##
============================================
+ Coverage     72.51%   72.63%   +0.12%     
  Complexity      175      175              
============================================
  Files            14       14              
  Lines          1819     1831      +12     
============================================
+ Hits           1319     1330      +11     
- Misses          500      501       +1     

Flag	Coverage Δ
multisite	72.63% <93.75%> (+0.12%)	⬆️
phpunit	71.32% <93.75%> (+0.13%)	⬆️

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