wall-framing-takeoff could already read ceiling joist positions from the roof layout (ceilingJoistsFromRoof), but only through the CLI plan file. The "Ceiling joist spacing" select on the page now has a "From the roof's ceiling joists" choice, and it round-trips through the saved plan.
It needs the roof turned on with a ceiling joist size. Checked only by source assertions in page.test.mjs, not clicked in a browser, and not against a real ceiling hang. Estimates only, not engineering or building-code advice.