Add filter hooks for AJAX suggest results

[apermo]

Problem

The "select translation" AJAX autocomplete (suggest_posts / suggest_terms) returns results with no way
to alter the final result set before it reaches the browser.

Existing filters operate upstream:

• msls_meta_box_suggest_args / msls_post_tag_suggest_args — modify query args before fetching
• msls_meta_box_suggest_post / msls_post_tag_suggest_term — modify individual items in the loop

There is no filter on the collected results array. This makes it impossible for add-on plugins to:

• Re-sort results (e.g., put heuristically likely matches first)
• Modify labels (e.g., add match-probability prefixes)
• Insert spacers or group separators
• Remove or reorder entries based on custom logic

Proposal

1. Two new filters on the final results

msls_meta_box_suggest_results (posts) and msls_post_tag_suggest_results (terms)

Applied after all items are collected and sorted, before JSON encoding. Each filter receives:

• $results — array<int, array{value: int, label: string}>, alphabetically sorted by default
• $context — associative array with blog_id, post_type (or taxonomy), s (search term), source_id

2. Pass source_id in the AJAX request

Currently the AJAX request does not include the ID of the post/term being edited. Without this, filter
consumers can't implement heuristic matching (e.g., "this post's title is similar to...").

Changes:

• Add a hidden field #msls_source_id in the metabox HTML (posts: $post->ID, terms: $tag->term_id)
• JS sends source_id in the AJAX POST data
• New FIELD_SOURCE_ID constant in MslsFields

Example usage

add_filter('msls_meta_box_suggest_results', function (array $results, array $context): array {
    // Access the source post for comparison
    $source = get_post($context['source_id']);

    // Score and sort by title similarity
    usort($results, function ($a, $b) use ($source) {
        $score_a = similar_text($source->post_title, $a['label']);
        $score_b = similar_text($source->post_title, $b['label']);
        return $score_b - $score_a;
    });

    // Prefix top match
    if (!empty($results)) {
        $results[0]['label'] = '⭐ ' . $results[0]['label'];
    }

    return $results;
}, 10, 2);

Files to modify

• includes/MslsFields.php — add FIELD_SOURCE_ID constant + config
• includes/MslsMetaBox.php — add hidden field in render_input(), add filter in suggest()
• includes/MslsPostTag.php — add hidden field in add_input()/edit_input(), add filter in suggest()
• src/msls.js — send source_id in AJAX request