Read the bounded, customer-scoped Workflow builder aggregate

Returns one selected agent's workflow draft (with a live, in-memory validation summary), the currently published version summary if any, and a bounded version history. Distinguishes an agent with zero workflows (workflow: null) from an existing draft. It also carries call_variables: {"active": false} until call variables are switched on, and then whether the AI agent looks callers up in a contact list (caller_lookup), which the draft's validation uses to walk protected values exactly as the draft update's response does. It is bound to the dashboard session organization and selected project; it never compiles server-side for a side effect, calls a provider, or performs a write.