Include theme header and footer in custom plugin

Question

I am working on a custom plugin. I created a custom post type inside my plugin. Now, for single posts I want to serve a custom template using my custom plugin without touching any theme file. The problem I am facing is that inside single post file, I can't use get_header() or get_footer() functions which is justified because these functions are meant for themes.

What other options I have to fetch theme's header and footer for my custom template for single post in my custom plugin?

This is the code I have so far which does not work:

<?php
function include_theme_header() {
    $header_path = get_template_directory() . '/header.php';

    if (file_exists($header_path)) {
        ob_start(); // Start output buffering to capture the header content
        include($header_path);
        $header_content = ob_get_clean(); // Get the captured header content and clean the buffer

        // Output or use $header_content as needed
        echo $header_content;
    }
}

function include_theme_footer() {
    $footer_path = get_template_directory() . '/footer.php';

    if (file_exists($footer_path)) {
        ob_start(); // Start output buffering to capture the header content
        include($footer_path);
        $footer_content = ob_get_clean(); // Get the captured header content and clean the buffer

        echo $footer_content;
    }
}




//SERVE CUSTOM TEMPLATE FOR EVENTS CUSTOM POST TYPE SINGLE POST

function custom_post_type_template($template) {
    global $post;

    // Check if this is a single post of your custom post type
    if ($post->post_type == 'event') {
        // Include the header
        include_theme_header();

        // Include your custom content
        include(plugin_dir_path(__FILE__) . 'templates/single-event.php');

        // Include the footer
        include_theme_footer();

        // Prevent WordPress from loading the default template
        exit;
    }

    return $template;
}

add_filter('template_include', 'custom_post_type_template');
?>