FP-17: Connection Guides

[steilerDev]

As a homeowner, I want to mark where utilities cross between adjacent walls and layers so that I can trace a utility line's full route through the building.

Parent Epic: #752 (EPIC-16: Floor Plans & Utility Tracking)
Priority: Should Have
Phase: 4 — Utilities

Acceptance Criteria

• 1. GET /api/floor-plans/connections with query params (layer_id or floor_id) returns connection guides
• 2. POST /api/floor-plans/connections creates a connection guide linking two layers with position, utility_type_id, and optional label
• 3. PATCH /api/floor-plans/connections/:id updates connection guide properties
• 4. DELETE /api/floor-plans/connections/:id deletes a connection guide
• 5. Connection guides are rendered as directional arrow markers at layer edges on the layer detail canvas
• 6. Each connection guide displays the utility type color and a small arrow indicating direction
• 7. Clicking a connection guide marker navigates to the connected layer's detail view
• 8. Connection guides between walls on the same floor are labeled "Adjacent Wall" connections
• 9. Optional punch-through visibility: mid-surface termination points can be marked where a utility exits one layer and enters the adjacent wall's layer
• 10. The connection list for a layer is shown in a side panel with source/destination layer info
• 11. Validation: both source and destination layers must exist; utility_type_id must be valid

Notes

• Dependencies: FP-13 (FP-13: Utility Lines Backend #765) — utility lines backend; FP-14 (FP-14: Layer Detail View (Read-Only) #766) — layer detail view
• Connection guides are metadata/navigation aids — they do not enforce that utility lines actually connect
• Cross-floor connections (vertical) are handled separately in FP-18