git checkout dev
git format-patch --stdout last_sync_tag > catchup.mbox
git checkout public
git am catchup.mbox
git --skip # talks about a missing file
git --skip # talks about a missing file
git --skip # talks about a missing file

dev: a-b-c-d-e-f-g-h-i-j-k
pub: t-u-v-w-x

checkout pub
rebase --onto pub i  # I really expected this to work

git checkout -b dev public
git am create-dev-only-files.patch
git checkout public
git merge -s ours dev
git checkout dev
# write more dev patches...
git checkout public
git merge dev
# and this should merge in the patches without bringing in the
#  dev-only files

git checkout -b dev public
git am create-dev-only-files.patch
git checkout public
git merge -s ours dev
git checkout dev
# write more dev patches...
git checkout public
git merge dev
# and this should merge in the patches without bringing in the
#  dev-only files

git rebase --onto <PH> <DevPH>

git rebase --onto pub h