Use Magento 2 asynchronous and bulk REST endpoints for high-volume catalog operations

Steps

1. Prefix any standard synchronous REST endpoint with `/async/V1/` for single async calls, or `/async/bulk/V1/` for batch operations; for example, bulk product upsert becomes `PUT /<store_code>/async/bulk/V1/products`.
2. Send an array of objects in the request body; the bulk endpoint splits the array into individual messages and writes each to the message queue, returning a `bulk_uuid` and array of `request_items`.
3. Ensure RabbitMQ (or an alternative message broker) is installed and configured; start the async consumer with `bin/magento queue:consumers:start async.operations.all`.
4. Poll operation status via `GET /V1/bulk/{bulk_uuid}/status` for a summary, or `GET /V1/bulk/{bulk_uuid}/operation-status/{status}` to count operations in a specific state (e.g., 4 = complete, 2 = failed).
5. For failed operations, retrieve error details from the operation status response and re-submit corrected records as a new bulk request.
6. Scope bulk requests to a specific store view by including the store code in the route (e.g., `PUT /en_US/async/bulk/V1/products`) to avoid updating the default scope unintentionally.