SOLUTION

Big shoutout to the wonderful SallyM, who answered this very succinctly in the comments of this post.

If it helps anybody, here's the code that I used.

Note: Replace the //CONTENT// with your own site content

function include_template_specific_css() {
if (is_page_template('//TEMPLATEFILENAMEWITHDIRECTORY//.php'))
    wp_enqueue_style('//CSSFILENAME//', get_template_directory_uri().'//CSSFILEURL//.css');
}
add_action('wp_enqueue_scripts', 'include_template_specific_css');

Good luck!

/SOLUTION

I'm attempting to call a specific stylesheet within the php of a new post template (one of four).

The stylesheet is 'Featured-Article.css'.
The template file is 'Featured-Article.php'.

Code I've attempted to place within the template includes:

<?php wp_enqueue_style('Featured-Article', get_stylesheet_directory_uri().'assets/css/Featured-Article.css',array('style')); ?>

and

<style> <?php include 'assets/css/Featured-Article.css'; ?> </style>

I'm wondering whether this is even possible at this point, short of meddling with functions.php to create a "if (is_page_template('Featured-Article.php')) etc" - something substantially beyond my ability!

Any ideas?

UPDATE 1:

It looks like the consensus is that such a callback must take place from within a theme's functions.php file. To this end, here's a draft code snippet that I'd hope might accomplish our aim, however sadly didn't work.

function //theme//_include_page_specific_css() {
if (is_page_template('Featured-Article.php'))
    wp_enqueue_style('Featured-Article', get_template_directory_uri(). '/assets/css/Featured-Article.css'); }


add_action('wp_enqueue_style', 'Featured-Article');
    }

Does anyone have any ideas?

UPDATE 2 - SOLVED

Big shoutout to the wonderful SallyM, who answered this very succinctly in the comments of this post.

If it helps anybody, here's the code that I used.

Note: Replace the //CONTENT// with your own site content

function include_template_specific_css() {
if (is_page_template('//TEMPLATEFILENAMEWITHDIRECTORY//.php'))
    wp_enqueue_style('//CSSFILENAME//', get_template_directory_uri().'//CSSFILEURL//.css');
}
add_action('wp_enqueue_scripts', 'include_template_specific_css');

Good luck!