Drag the porch and lean-to the same way

Direct manipulation for additions with the same architecture as the main building: the renderer reports the requested value and one pure, total resolver holds all the judgement — ladders, engineering limits and the shell cap.

Also called: addition controls · projection handle · attach height · slide along the wall · centre the porch

1. 1HANDLE ISOLATION: each tab writes ONLY its field. Pitch never changes width, slide or attach; attach never changes pitch or span; width never changes pitch.
2. 2If a requested value would poke the peak through the main overhang or bury a lean-to eave, THAT handle stops — the drag walks back toward the last legal value along only the fields the handle owns.
3. 3Extent is always written as an (offset, length) pair from a pinned edge captured at pointer-down, so sequential end drags cannot walk the far end out to the corner.
4. 4ALT on an extent tab is Figma-symmetric: both ends move about the centre at grab time.
5. 5Snapping: projection lands on the published width/depth ladders, pitch on whole rise-in-12, attach on whole feet, extent ends on the main building's BAY LINES so addition columns line up with the building's.
6. 6Sliding is different: only the wall CENTRE is a magnet — Keith said bay clicks on a slide feel like noise — so off-centre the offset follows the pointer with no grid.
7. 7A selected addition's volume is itself a grab surface for sliding it along the wall.
8. 8Minimum roof slope is enforced as a BLOCKING rule on the pitch handle.

• ◆Coupled fields where one handle silently changes another.
• ◆Extent drags that drift because they resolve against stale state.