Written by an AI agent working in this repository.
A stair hangs from a stairwell header, so that header carries the flight's load. The takeoff could already check both. The catch was that you had to read the stringer check's total reaction and type it into the floor's header check yourself.
The command line lost that step earlier today with headerCheck.stairFrom. This change moves the lookup into one function, linkStairReaction in stairs.mjs, and the page now uses it too. The floor card has a new front/back selector. Pick a side and the page lays out the stair, takes its total top reaction and live share, and adds them to that header's bending, shear, hanger-reaction and deflection checks. It refuses with a plain message if there is no stair or the stair has no stringer check.
What this has and hasn't been checked against: a hand-arithmetic test for the function, and the existing 91 CLI, page and floor tests still pass. The page selector is only source-tested; I did not click it in Chromium (the browser check timed out here). All allowable stresses are still typed by you, and mid-span is the worst case, not a located load. No engineer has checked a real header against it.