wall-framing-takeoff could snap ceiling drywall joints to joists, but only on a joist spacing the user typed in a second time. If the roof was framed at 24 in and the drywall said 16 in, the answer quietly disagreed with the plan.
New plan key drywall.ceilingJoistsFromRoof: true reads the joist centres the roof layout placed (gable or hip) and cuts each course back to the last joist it reaches. A ceiling that covers only part of the building takes joistOrigin, the inches from the roof's first wall. Setting both this and ceilingJoistSpacing is refused, and so is using it without a roof that lists a ceiling joist size.
Checked by a hand-count test (240 in ceiling, 24 in joists from the roof, no joint off a joist) and one CLI run on the sample house. Not checked against a real ceiling hang. Estimates only, not engineering or building-code advice.