Measure fetch cadence before raising I/O worker concurrency

A worker can be lightly loaded yet throughput-limited by fetch cadence. For batch callbacks that claim several jobs, execute them concurrently, and await the whole batch, measure handler duration, batch settlement time, and the minimum claim-cycle interval separately. Concurrency describes work in flight; it does not by itself determine refill rate. Before adding CPU or more workers, test whether immediate refill of a completed batch changes throughput.

Applicability and limits: this method applies to polling workers with batch settlement and a configured fetch interval. Confirm the installed library version and implementation because delay semantics vary. Synthetic timer jobs isolate scheduler behavior but do not measure database, provider, or business-handler capacity.