Post-quantum migration is not one migration. Cryptography is embedded across business services, platforms, identities, trust infrastructure and external relationships, and those dependencies do not all move together.

A fictional automotive order-to-delivery case follows one function, machine authentication, through four enterprise situations, then moves the assumptions underneath the plan: a replacement slips, a retirement extends, a partner stays uncertain. The cryptographic finding does not change. The executable plan does, and so does the date by which you have to decide.