Debug a WordPress PHP fatal error

A client's site just went down with this in the debug log:

[PHP Fatal error: Uncaught Error: Call to undefined function wc_get_product() in
/wp-content/themes/client-theme/functions.php:212]

CONTEXT: [this line was added to functions.php yesterday to show a custom "related
products" block on single product pages; WooCommerce is active, but this error
started right after a WooCommerce update]
ENVIRONMENT: PHP 8.2, WordPress 6.7

Work this the way a senior dev would triage a site-down ticket, in order:
1. Translate the error precisely: which function is missing, and why would a
   function that clearly depends on WooCommerce be undefined when WooCommerce is
   active? Reason toward load order and hook timing, not just "WooCommerce isn't
   installed."
2. State the most likely root cause given the context: is this a load-order bug (the
   function is called before WooCommerce has finished loading, e.g. outside a
   `woocommerce_loaded` or `init` hook) or a genuine incompatibility introduced by
   the update?
3. Give the exact code fix as a before/after diff, showing the correct hook to wrap
   the code in.
4. Give a separate, immediate mitigation to get the site back up right now (e.g.
   comment out the specific function call via SFTP). Assume there's no staging site
   and this needs to happen in the next 5 minutes.
5. Flag whether this bug pattern, calling a plugin function directly in a theme
   without a hook or `function_exists` guard, is likely to recur elsewhere in this
   theme, and where to check.

Replace the error, context, and environment details with your actual situation.