Refactor delay calculation and add test for invalid delay path

Editor assessment

The subject opens with the redundant pairing 'refactor: refactor delay calculation', then adds a second strand, a test for the invalid delay path, blurring the unit of work. The content is real: delay calculation was reworked and a previously untested failure path gained coverage. No scope, no body explaining what was wrong with the old calculation or what counts as an invalid delay, the useful part. Hygiene suffers on the stutter. Understandable with effort, valid, and thin, with the doubled verb setting a careless tone.