Xdebug disconnects over a Watch expression evaluation fail

This is one of those entries where I've spent several frustrating days fighting with a problem, solved it finally, and want this solution to be googleable for future generations. Let me set the scene: a PHP website,

Forky...

GitHub should provide an option to mark repo forks with intention, so that you can distinguish between forks made because one wants to contribute to the original, and forks made because one wants to supplant the original. The former might evolve into the latter over time though.