Scoped gitpush proceeds unserialised when hub identity is missing in shared checkout

Observed on Terra TERRA-254 record push dd6ac01 and TERRA-282 allocator push 9172c13: gitpush.sh reports GITPUSH-GATE-BYPASS no hub identity (hub/bearer unset), proceeding UNSERIALISED under load ceiling. The normal pre-push migration/app gates still ran; this is a separate coordination gap. In one shared checkout, concurrent agents can alter HEAD/index or push a prior lane commit before its scoped review. Define who supplies hub identity and make scoped pushes serialize or refuse when that primitive is absent; exercise a forced competing-push case. Do not bypass ordinary migration hooks. No data loss observed in these two pushes.