Function probe_device_capacity 

pub fn probe_device_capacity(
    device_ordinal: usize,
    memory_ownership: GpuMemoryOwnership,
    backend_reserve_bytes: u64,
) -> Result<GpuDeviceCapacityProbe>

Queries declarable capacity for one device without building a backend.

This probe acquires no live-backend lease and installs no memory manager. Setting the explicit limit to at most max_declarable_limit_bytes ensures the build will not fail on capacity limits. Refusals carry the same reason facts reported by backend initialization.