composer update not applying patches to drupal core

Turns out that’s sort of exactly what’s happening:

Drupal core patches apply incorrectly if they only add new files

So, so, so many dead ends with this (although this person might possibly have been hitting the same problem?)

The key is that it silently fails. People have trouble with patching and compeser-applied patches all the time! This is different.

composer.json not applying patchs from theme (nope, that wasn’t the problem!)

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