The install is a detached-HEAD checkout of a pinned commit. Without
--branch, 'hermes update' fell back to its default (main) and switched
the checkout to main — a divergent branch that lacks the desktop CLI
command — so the update targeted the wrong branch and the rebuild stage
failed with 'invalid choice: desktop'.
Thread BUILD_PIN_BRANCH (the branch this installer was built against,
and the same branch the desktop detected the update on) into
'hermes update --branch <b>' so update + rebuild stay on-branch.