batch_register_instance
Batch-register product instances against canonical entities in one atomic call (the migration counterpart to `register_instance`). Validates every instance up front (canonical exists, same-type) then writes all `instance_of` edges and flushes once. Per-instance idempotent; `alias` honoured per instance.
Workspace & Portfoliosvalidate-all-then-write. A single invalid instance rejects the whole batch.
Arguments
instancesarrayrequiredUp to 50 instances.
Returns
Shape
{ results: [...], registered, already_existed, count, portfolio_file }