In the meantime, I updated the PR and took into account the remarks from @Seldaek.
The phase 1 of the builder (the FOD) doesn’t generate the autoload files thanks to --no-autoload AND now also delete the bin-dir (rm -rf $(composer config bin-dir)) directory.
In the phase 2, two steps are now being done:
composer dump-autoloadcomposer install(to reinstall thebin-dir)
It seems to work fine so far.
Looking for comments and tests please!