The people making the architectural decisions are the people in the room with you, from the first meeting to delivery. There is no account-management layer, and no handoff to another team once the contract is signed.
Leads discovery and the data model. Owns the scope boundaries and the architectural decisions that are settled before development starts.
Owns infrastructure, integrations and data migration from the systems already in place. Leads go-live and keeps the system stable after it.
The proposal derives from an agreed discovery document. A scope change is documented and priced, not argued about mid-project.
The code, the databases and the infrastructure are in your name from day one. No vendor lock-in.
A version you can run exists from the first iteration, not only at delivery.
Runbook, data schema and operational documentation ship with the system, not after it.