Stability enhancements

[mathetos]

When HTML-to-Markdown conversion fails (e.g., malformed or unusual HTML), there is no way for developers to control the fallback. Once conversion is wrapped in try/catch and a default fallback (like wp_strip_all_tags) is used, theme and plugin authors may want to customize that fallback—for example, to use a different fallback, adjust formatting, or log/handle the error.

Describe the solution you'd like

Introduce a filter that runs when conversion throws, so the fallback text can be customized:

$body = apply_filters(
    'markdown_alternate_conversion_error_fallback',
    wp_strip_all_tags($content),  // default fallback
    $content,
    $post,
    $e
);

Filter arguments:

1. string — The default fallback (e.g. wp_strip_all_tags($content))
2. string — Original HTML content
3. WP_Post — The post object
4. Throwable — The caught exception

Return: The string to use as the markdown body when conversion fails.

Why do you think this feature is something we should consider for this plugin?

• Lets developers adapt fallback behavior without editing plugin code.
• Aligns with common WordPress plugin patterns (filters for customization).
• Keeps the plugin extensible while still providing a safe default.

Additional context

This complements a bug fix that wraps the League HTML-to-Markdown conversion in try/catch and uses wp_strip_all_tags as the default fallback. The filter only runs when an exception is thrown; it does not run for successful conversions.