Chromium fails to build on !amd64: snapcraft complains that the 'pull' step of 'gtk3-locales' is out of date

Indeed, and I now remember I read about it here. Thanks for the tip! That doesn’t explain why the build is failing only on !amd64 though.

Is there a $SNAPCRAFT_* variable that points to the root of the tree, where that patches/ directory lives? Or a mechanism to have it copied over to the part’s source directory before building?

Ack, I will apply the workaround there too, thanks for the suggestion.