Continue the Calder Yards change-management case using HANDOFF.json and the connected Laydyne MCP. This is a new AI session with the same browser-local project. Keep all existing saved options, comparison results and history. Work only through MCP on the model, sequentially, using current expectedRevision for each write.

The designer has a second change to show the client: add two residential floors by copying L18 to L19 and L20, carrying the existing residential/service lifts and both stairs up. This is a geometric capacity study. Do not increase or invent the resident arrivals, certify structure or escape safety, or infer that the old demand still validates a larger occupied building.

1. Confirm the current layout is UC5 B and record its floor count, floor areas, residential room count and connections.
2. Add L19 (name L19 Homes, level 19, structure CY, copyFrom L18) and L20 (name L20 Homes, level 20, structure CY, copyFrom L18). Add the eight connections from the existing script:
   - Residential elevator L18–L19 and L19–L20, at x16.52/z19.6 on both ends, speed1.6, capacity10, cars2, doorSeconds4, dwellSeconds4.
   - Service elevator L18–L19 and L19–L20, at x20.23/z19.6, speed1.6, capacity6, cars1, doorSeconds6, dwellSeconds6.
   - Stairs A and B on each new floor transition, width1.2, x24.75. L18–L19: A z7.8→12.3, B z13.7→18.2. L19–L20: A z12.3→7.8, B z18.2→13.7. Use stable readable labels for each connection.
3. Before saving another option, use Undo immediately after this floor edit and verify the original floor count. Then Redo and verify both floors/connections return. Read-only checks may be made between these calls. Do not accidentally undo a later save instead of the floor edit.
4. Check all floors. Save design option UC5 C — café extended and two homes floors (id uc5-c). Compare A→C and B→C, including added floors, parts, floor area, residential rooms and connections. Use real quantities and change history; distinguish construction capacity from demonstrated operating capacity.
5. Update the existing named browser project from HANDOFF.json with expectedProjectRevision. Update HANDOFF.json with all new IDs, the saved revision and geometry hash. Write S2-results.md with the actual quantities, Undo/Redo confirmation, unresolved findings and limitations. Keep all A/B/C input snapshots and the actual saved A/B process comparison.

The recording operator will collect the full project, comparison data and illustrated handout separately after this step. Do not remove needed evidence to make a download smaller. No new hypothetical case or model comparison is needed.