为一个地址创建并激活订阅：校验地址、扣取激活费并开始委托能量。要求余额满足入门门槛（激活费 + 一次每日费 + 一次 131k 单元）。一个地址只能持有一个有效订阅，因此对活跃地址而言该调用天然幂等——重复调用返回 409 address_busy。

请求

Responses

Subscription created and activated.

insufficient_balance — balance can't cover the entry threshold; or plan_not_found.

address_busy — the address already has a live subscription; or address_exists — a closed subscription exists (reactivate or delete first).

invalid_address — the address is malformed.

fulfiller_unavailable — the energy provider could not activate the delegation.